super+volcano

toc =Definitions=

> "Dark-colored, low-silica (less than 53 percent SiO2), low viscosity volcanic rock that is relatively fluid when molten; eruptions of basalt are generally non explosive and tend to produce relatively long thin lava flows." > "A large volcanic depression, commonly circular or elliptical when seen from above." > "A volcanologic calculation used to estimate volcanic eruption volume. One of the widely accepted measures of the size of a historic or prehistoric eruption is the volume of magma ejected as pumice and volcanic ash, known as tephra during an explosive phase of the eruption, or the volume of lava extruded during an effusive phase of a volcanic eruption. Eruption volumes are commonly expressed in cubic kilometers (km3).
 * Basalt**
 * Caldera**
 * Dense-rock equivalent**

> Historical and geological estimates of tephra volumes are usually obtained by mapping the distribution and thickness of tephra deposits on the ground after the eruption is over. For historical volcanic explosions, further estimates must be made of tephra deposits that might have changed significantly over time by other geological processes including erosion. Tephra volumes measured in this way must then be corrected for void spaces (vesicles - bubbles within the pumice, empty spaces between individual pieces of pumice or ash) to get an estimate of the original volume of magma erupted. This correction can be made by comparing the bulk density of the tephra deposit with the known density of the original gas-free rock-type that makes up the tephra. The result is referred to as the dense-rock equivalent of the erupted volume." > "Material that is thrown out by a volcano, including pyroclastic material (tephra) and, from some volcanoes, lava bombs." > Intensity (effectively, the “violence”) of an eruption is measured in cubic metres, or mass, of magma erupted per second. > "A flowing mixture of water-saturated rock debris that forms on the slopes of a volcano, and moves downslope under the force of gravity, sometimes referred to as debris flow or mudflow." > "Molten rock that erupts from a vent of fissure, see Magma." > "Molten rock that contains dissolved gas and crystals, formed deep within the Earth. When magma reaches the surface, it is called lava." > "The volume or mass of magma erupted." > "A hot (300-800 °C), dry, fast-moving (10 to more than 100 meters per second) and high-density mixture of ash, pumice, rock fragments, and gas formed during explosive eruptions or from the collapse of a lava dome. Moves away from a volcano at high speeds." > "A powerful volcano, often having an explosive or cataclysmic eruptions." > “Supervolcanic eruptions are defined as those where at least 1000 km3 of tephra were produced during the eruption, and these classify as VEI 8 or greater.” > "Materials of all sizes and types that are erupted from a volcano and deposited from the air." > "A pyroclastic igneous rock composed of volcanic ash and fragmented pumice, formed when accumulations of the debris cement together." > "An opening in the Earth's surface through which volcanic materials (magma and gas) escape. Vents can be at a volcano's summit or on its slopes; they can be circular (craters) or linear (fissures)." > "Measure of the fluidity of a substance. Basalt is less viscous than dacite." > “The Volcanic Explosivity Index (VEI; Newhall and Self, 1982) provides a measure of the magnitude of an eruption based on a combination of erupted tephra volume and eruption plume height. The index uses a semi-quantitative logarithmic scale where each successive value of the index represents 10× greater volume of material erupted."
 * Ejecta**
 * Intensity**
 * Lahar**
 * Lava**
 * Magma**
 * Magnitude**
 * Pyroclastic flow**
 * Supervolcano**
 * Supereruption**
 * Tephra**
 * Tuff**
 * Vent**
 * Viscosity**
 * Volcanic Explosivity Index (VEI)**

=Introduction=

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A super-volcano is an arbitrary definition for volcanoes that are capable of the most explosive eruptions. Such super-eruptions, sometimes defined as those ejecting more than 1000 km3 of tephra and classifying as VEI 8, have extensive environmental impact that threaten global civilization.

Global trade and food production, air travel and space-borne communication will all be at risk if a super-eruption occurred. It could ruin world agriculture, severely disrupt food supplies, and cause mass starvation. An area the size of North America or Europe could be devastated but beyond the immediate destruction, gases released during an eruption can disrupt global climate dramatically for years afterward. The environmental effects can threaten the fabric of civilisation.

Events of mass extinction have been linked to previous super-eruptions, e.g. an eruption at the Siberian Traps may explain the Permian extinction 250 million years ago where 90% of marine species where wiped out.

"The last time (a supervolcano) erupted was 74,000 years ago, when Toba, on the Indonesian island of Sumatra threw out nearly twice the volume of Mount Everest in magma. Toba was more than 5000 times as explosive as the eruption of Mount St Helens in 1980 and comes in as an eight on the VEI scale. There is much debate about how devastating Toba was for humans, but without a doubt it will have had a very severe impact. Some scientists argue that it may even have caused a bottleneck in human evolution."

"Ancient Neanderthals may have gone extinct as a result of volcanic eruptions devastating their western Asian and European homelands, Russian researchers say. A team led by archaeologist Liubov Golovanova of the ANO Laboratory of Prehistory in St. Petersburg says at least three volcanic eruptions about 40,000 years ago led to the end for the humanlike hominids, ScienceNews.org reports. Modern humans survived because they lived in Africa and on the tip of southwestern Asia at that time, safely outside the range of volcanic ash clouds, Golovanova's group says. That geographic good luck allowed Homo sapiens to move into Neanderthals' former territory after a couple of thousand years without having to compete with them for food and other resources, the research suggests. Modern man's survival in harsh, post-volcanic habitats was possible with advances in stone tool making and other cultural innovations achieved shortly after 40,000 years ago, Golovanova and his colleagues suggest. Evidence for the volcanic theory comes from soil, pollen, animal bones and stone tools from Mezmaiskaya Cave in southwestern Russia's Caucasus Mountains, Golovanova says. Chemical analyses of soil layers in the Russian cave identified two types of volcanic ash suggesting separate volcanic eruptions in western Asia between 45,000 and 40,000 years ago."

The probability of a super-eruption of occurring in terms of a human lifespan is small, but on a geological time scale they are surprisingly common (occurring on average every 100,000 years); an eruption with potentially catastrophic consequences for mankind will happen again, it’s just a question of when.

Small-scale super-eruptions are common compared to other naturally occurring devastation phenomena like asteroid impacts. The effects of a medium-scale eruption would be similar to an impact of a 1km asteroid, but are five to ten times more likely to occur within the next few thousand years. It is one of the most dramatic natural disasters humans could be faced with.

An eruption of 300km3 of magma (equivalent to 750km3 of volcanic ash) would have global consequences and represents the lower end of the super-eruption spectrum.

Geological evidence and models suggests intensities of up to 100 million m3 per second are possible.

At present there are no conceivable way of preventing an eruption, and because super-volcanoes are not easily detectable from the surface it is hard to predict where the next one could occur.

"Supervolcanoes tend to be active over millions of years. They erupt less frequently than other volcanoes, but when they do erupt, they are substantially more intense."

“...caldera-forming eruptions (CFEs) are associated with extreme hazard and environmental impact at all scales...”

"...a pole shift could be the trigger for an eruption..."

"Problems such as global warming, impacts by asteroids and comets, rapid use of natural resources, and nuclear waste disposal require world leaders and governments to address issues with very long-term consequences for the global community. Sooner or later a super-eruption will happen on Earth and this is an issue that also demands serious attention. While it may in the future be possible to deflect asteroids or somehow avoid their impact, we know of no strategies for reducing the power of major volcanic eruptions. Even science fiction cannot produce a credible mechanism for averting a super-eruption. We can, however, work to better understand the mechanisms involved in super-eruptions, with the goal of being able to predict them ahead of time and provide a warning for society. Preparedness is the key to mitigation of the disasterous effects of a super-eruption."

=Timeline=

> ==Formation==

“No matter the heat source, pressure in the magma chambers builds over time as more magma collects under the enormous weight of overlying rock. A supereruption occurs after the pressurized magma raises overlying crust enough to create vertical fractures that extend to the planet's surface. Magma surges upward along these new cracks one by one, eventually forming a ring of erupting vents. When the vents merge with one another, the massive cylinder of land inside the ring has nothing to support it. This “roof” of solid rock plunges down—either as a single piston or as piecemeal blocks—into the remaining magma below, like the roof of a house falling down when the walls give way. This collapse forces additional lava and gas out violently around the edges of the ring.”

“The rate at which magma leaves a chamber depends primarily on two factors: the magma's viscosity, or ability to flow, and the pressure difference between the chamber and the earth's surface. Because the pressure inside a bubble matches that of the chamber where the magma formed, the bubble acts like a mini version of the chamber itself.”

“...the super-sized nature of supervolcanic systems (Volcanic Explosivity Indices of 8 and above) is thought to require an elevated basaltic flux from the mantle that provides a thermal and mechanical environment supportive of large-scale silicic magma production and storage (Hildreth, 1981; Best and Christiansen, 1991; de Silva and Gosnold, 2007). The largest CFEs, those of super- volcanic proportions, occur during major caldera-forming events that sample the tops off these magma systems. The eruptions may occur at individual centers with protracted histories like Toba (Indonesia) (Chesner et al., 1991), Cerro Galan (Argentina) (Sparks et al., 1985), and Valles (New Mexico) (Self et al., 1986)). Alternatively eruptions may be part of regional episodes of supervolcanism known as ignimbrite flare-ups, where multiple eruptions from spatially and temporally related centers map out the development of an upper-crustal batholith beneath. Such volcanic flare-ups have been described from western North America (Coney, 1972), the Sierra Madre Occidental, Mexico (Ferrari et al. 2002), and the Altiplano Puna volcanic complex of the Andes (de Silva, 1989; de Silva et al., 2006). A plutonic connection to these surface flare-ups may be found in the Sierra Nevada of California (Ducea, 2001) and other cor- dilleran batholiths (Lipman, 2007). Thermal and mechanical maturation of the crustal column as a result of protracted magmatism has been con- noted to be an essential factor in the development of these supervolcanic systems (de Silva and Gosnold, 2007; Lipman, 2007).”

“...it is not simply duration, but the magnitude of the mantle flux that is important, and de Silva and Gosnold (2007) have drawn a distinction between a steady-state arc (“normal” of Hughes and Mahood) and an arc in flare-up mode (Fig. 1); originally articulated by Hildreth (1981) as low-flux and high-flux systems. Under steady-state arc conditions, basaltic magma flux may focus locally to produce CFEs as large as VEI 6 and rarely 7 (10– 100 km3 of magma), but CFEs of supervolcanic proportion are not known. Conversely, under flare-up conditions, triggered by some major change in the mantle magma productivity, such eruptions are the culmination of extraordinary silicic magma productivity that results from the elevated power input from the mantle. Magma production rates in the two modes of arc operation are quite different. The most rapidly developing steady-state arc systems like the Aleutians are estimated to have magma production rates of 1.8 × 10−4 km3 km–1 yr–1 (Jicha et al., 2006), while magma production rates during the flare-up of the Altiplano Puna volcanic complex were as high as 6 × 10−3 km3 km–1 yr–1 (de Silva and Gosnold, 2007), an order of magnitude higher. One of the consequences of this elevated flux during flare-up mode is that the crust undergoes a thermomechanical evolution that promotes supervolcanic CFEs through the positive feed- back between mantle power, magma production, and advection of heat through the crust and the impact on the mechanical strength of the crust (de Silva et al., 2006; de Silva and Gosnold, 2007). Under a normal arc flux, the lack of correlation between CFEs and the duration of arc activ- ity found by Hughes and Mahood suggests that the feedbacks are muted, and thermal maturation is at a level where the CFE magnitude is buffered at a lower level.”

“The Taupo volcanic zone, which is one of the most prolific modern CFE [caldera forming eruption] provinces on Earth, exemplifies the situation where magma is erupted as a function of the extension rate in highly extended, young, thin continental crust.”

“In Toba, the source of the chamber is different. That region lies above a subduction zone, an area where one tectonic plate is slipping under another; the convergence produces widespread heating, mainly through partial melting of the mantle above the sinking plate.”

“Under the surface of Yellowstone, the North American tectonic plate is moving over a buoyant plume of warm, viscous rock rising through the mantle, the 2,900-kilometer-thick layer of the earth's interior that is sandwiched between the molten core and the relatively thin veneer of outer crust. Functioning like a colossal Bunsen burner, this so-called hot spot has melted enough overlying crust to fuel catastrophic eruptions for the past 16 million years.”

“One of the best-studied examples of supervolcano aftermath is the Bishop tuff, a volcanic layer tens to hundreds of meters thick that is exposed at the earth's surface as the Volcanic Tablelands in eastern California. This massive deposit represents what is left of the estimated 750 cubic kilometers of magma ejected during the formation of the Long Valley supervolcano caldera some 760,000 years ago.”

“...geologists now think that the Bishop tuff—and probably most other supererupted debris—was expelled in a single event lasting a mere 10 to 100 hours.”



>> ===Warning Signs===

"We know of roughly 50 supervolcanoes that have ever existed, and most of those are now extinct. Others are believed to be dormant, while a few are currently active - listed here under their common names:


 * Toba (Sumatra, Indonesia) - supereruption 74,000 years ago, which was the largest volcanic eruption anywhere on Earth within the last 25 million years. Most humans did not survive this eruption, and in theory it caused a population bottleneck that may have contributed to our evolution, or at least our genetic makeup. Toba may have been active within the last several hundred years
 * Yellowstone (USA) - last erupted 630,000 years ago. It has been speculated that the force of a Yellowstone eruption would be the equivalent of one thousand Hiroshima bombs exploding per second (3)
 * Long Valley (California, USA) - last erupted 760,000 years ago (600 km³ of ejecta).
 * Valles Caldera (New Mexico, USA) - last erupted 1.15 million years ago (600 km³ of ejecta)
 * Lake Taupo (New Zealand) - supereruption just 26,500 years ago. Has erupted roughly every thousand years since, with the most recent, 1,800 years ago, being considered the largest in recorded history, 100x larger than Mt St Helens. Fortunately it was not recorded, for New Zealand was yet to be settled by humans.
 * Phlegraean Fields (Naples, Italy) - supererupted 39,000 years ago (500 km³ of ejecta), with other major eruptions since. Could have a major eruption within decades.

Active - but no evidence they are capable of wiping us out


 * Kikai Caldera (Japan) - supererupted 6,300 years ago. Still active, with minor eruptions occuring as recently as 2004
 * Laacher See (Germany) - potentially still active, erupted 12,900 years ago
 * Mount Tambora (Sumbawa, Indonesia) - last erupted in 1815, killing at least 71,000 people.
 * Aira (Japan) - erupted 22,000 years ago (400 km³ of ejecta), but is still very active. In 1914 an eruption caused the evacuation of 23,000 people. The city of Kagoshima is very close by."

"Any eruption on the scale considered would be characterised by abundant and obvious precursor activity, so humankind should not be taken by surprise. Our recent civilisation has not suffered from a super-eruption and so large-scale volcanic symptoms have not been experienced. The time scales and types of super-eruption signals around a candidate volcano can be understood by scaling up from smaller events. The expected signs are seismic unrest, ground heating and swelling, change in groundwater temperature and chemistry, and in the composition and flux of volcanic gas. Many of these changes are nowadays routinely measured at super-volcanoes such as the Phlegrean Fields, Italy, and Yellowstone and Long Valley, USA. However, other potentially active super-volcanoes are not currently monitored."

"[Phlegraean Fields] is also showing signs of unrest. Containing a large portion of the city of Naples, a supereruption similar to the one 39,000 years ago would devestate Europe. Since the late 60s the caldera has risen by 3 metres. Even more worrying, scientists are preparing to drill into the volcano, an act that some experts consider irresponsible, and could result in an eruption."

“If a new round of small, precursor eruptions begins in Yellowstone—and they usually do so weeks to hundreds of years before a catastrophic explosion—testing the oxygen fingerprint of those lavas and the ages of their zircons should reveal what type of magma is abundant in the chamber below. If the next eruption is depleted in oxygen 18, then it is most likely still being fed by stagnant remnants of the original magma, which by now is probably more of a thick crystal mush than an explosive liquid. On the other hand, if the new lava carries the fingerprint of fresh magma from the mantle and does not contain old zircons, then it very likely came from a large volume of new magma that has filled the chamber from below. Such findings would imply that a new cycle of volcanism had commenced—and that the newly engorged magma chamber had more potential to explode catastrophically.”

"Two years prior to the Mt St Helens eruption of 1980, scientists predicted that an eruption would occur within 22 years. But would such information be made public about an imminent Yellowstone eruption? For example, if a study predicted an eruption in the next 10 years, the economic upheaval created by half of America relocating could be too much to bear. Leaders might choose to ignore the possibility and cross their fingers. Like they (unfortunately) did with New Orleans. Plenty of conspiracy theorists have discussed the possibility of governmental secrecy (at the Above Top Secret forum, the Yellowstone topic has over 600 pages of posts), but of course proof is lacking otherwise it would be fact, not theory."

"The Yellowstone caldera is an active place, and there are regular reports that could cause some people to be concerned. Unfortuanately, because we have only been monitoring this area for less than a century, it's impossible to tell whether the current activity is relatively normal, or if it is unusual and an indicator that something is up.

A 25 mile section of the caldera rose 5 inches between 1997 and 2003. Prior to this, the whole caldera has risen, fallen, risen, fallen. Between 1923 and 1975 it rose 3-4 feet. Geysers start and stop mysteriously. In an average year the region has thousands of earthquakes too small for people to feel underneath them."

"Long Valley is rated by the U.S. Geological Survey as a bigger risk than Yellowstone. Magma is bubbling beneath the surface, and strong earthquakes are not uncommon - in 1980 it had four which measured 6 on the Richter Scale. Paoha Island in the neaby Mono Lake was created from an eruption just 350 years ago."

[|Carbon Dioxide and Helium Discharge from Mammoth Mountain, Long Valley caldera, California]

[|Living With a Restless Caldera—Long Valley, California]

"...there are many other areas where a supervolcano could pop up, including Indonesia, the Philippines, several Central American countries, the Andes, Japan, the Kamchatka peninsula in eastern Russia, and even Europe (the area around Kos and Nisyros in the Aegean Sea might be a supervolcano)."

>> ===Monitoring volcanoes===

[|Monitoring super-volcanoes: geophysical and geochemical signals at Yellowstone and other large caldera systems] Jacob B. Lowenstern, Robert B. Smith, David P. Hill

[|Toward "Supervolcano" Technology] Gillian R. Foulger

[|Monitoring Volcanoes]

> ==Eruption==



"By defining the low end of the super-eruption size spectrum as “those exceeding 300 cubic kilometres of magma erupted” we bring attention to events common enough to have reasonable odds of recurring within a human lifetime, but which are rare enough not to have been witnessed by our civilisation. We expect that such an eruption would produce significant, widespread and devastating effects affecting the whole globe if it came from a volcano located within a zone between 30°N and 30°S – where many volcanoes lie."

“...these eruptions feature supersonic blasts of superheated, foamlike gas and ash that rise buoyantly all the way into the earth's stratosphere, 50 kilometers high.As the land above the magma chamber collapses, immense gray clouds called pyroclastic flows burst out horizontally all around the caldera. These flows are an intermediate stage between lava and ash, so they move extremely rapidly—up to 400 kilometers an hour, some sources say; cars and even small airplanes would have no chance of outrunning them. These flows are also intensely hot—600 to 700 degrees Celsius—so they burn and bury everything for tens of kilometers in every direction.”

"The effects of a super-eruption on the areas in the immediate vicinity of the volcano are completely catastrophic. Explosive super-eruptions produce huge incandescent hurricanes known as pyroclastic flows, which can cover thousands to tens of thousands of square kilometres in thick deposits of hot ash. No living beings caught by a pyroclastic flow survive. However, these dramatic local effects are not of greatest worldwide concern. Globally, most repercussions will come from the effects of the volcanic ash and volcanic gases suddenly released into the atmosphere.

Volcanic ash fallout from a super-eruption will probably have severe effects over areas the size of a large continent. One centimetre thickness of volcanic ash is easily enough to disrupt most forms of agriculture, and lesser amounts (a few millimetres) can destroy many kinds of crops. A super-eruption can cover tens of millions of square kilometres in several centimetres of ash.

The most vulnerable areas are North and South America and Asia, when account is taken of locations of such volcanoes. Europe has at least one supervolcano (the Phlegrean Fields). It is possible that the area around Kos and Nisyros in the Aegean Sea might be a super-volcano. If such an eruption were to take place at any of these sites, then a substantial part of the global economy would inevitably be devastated and many parts severely incapacitated. Any technologically advanced city would be very vulnerable to the effects of ash, including pollution of water supplies, disruption of transport systems, and failure of electronic equipment. There would also be severe disruption of aviation.

The most significant global threat from super-eruptions is, however, to global climate and weather. Large explosive volcanic eruptions eject huge amounts of volcanic dust and gas into the stratosphere. The gases are dominated by water vapour, but also commonly include significant amounts of sulphur dioxide, carbon dioxide and chlorine. A great deal has been learnt over the last few decades on the effects of volcanic dusts and gases about climate, from careful examination of climate records and observations on eruptions."

>> ===Pyroclastic Flows===



“Pyroclastic flows are high-density mixtures of hot, dry rock fragments and hot gases that move away from the vent that erupted them at high speeds. They may result from the explosive eruption of molten or solid rock fragments, or both. They may also result from the nonexplosive eruption of lava when parts of dome or a thick lava flow collapses down a steep slope. Most pyroclastic flows consist of two parts: a basal flow of coarse fragments that moves along the ground, and a turbulent cloud of ash that rises above the basal flow. Ash may fall from this cloud over a wide area downwind from the pyroclastic flow.A pyroclastic flow will destroy nearly everything in its path. With rock fragments ranging in size from ash to boulders traveling across the ground at speeds typically greater than 80 km per hour, pyroclastic flows knock down, shatter, bury or carry away nearly all objects and structures in their way. The extreme temperatures of rocks and gas inside pyroclastic flows, generally between 200°C and 700°C, can cause combustible material to burn, especially petroleum products, wood, vegetation, and houses.

Pyroclastic flows vary considerably in size and speed, but even relatively small flows that move less than 5 km from a volcano can destroy buildings, forests, and farmland. And on the margins of pyroclastic flows, death and serious injury to people and animals may result from burns and inhalation of hot ash and gases.

Pyroclastic flows generally follow valleys or other low-lying areas and, depending on the volume of rock debris carried by the flow, they can deposit layers of loose rock fragments to depths ranging from less than one meter to more than 200 m. Such loose layers of ash and volcanic rock debris in valleys and on hillslopes can lead to lahars indirectly by:

1. Damming or blocking tributary streams, which may cause water to form a lake behind the blockage, overtop and erode the blockage, and mix with the rock fragments as it rushes downstream (for example, see this case study at Pinatubo Volcano, Philippines)

2. Increasing the rate of stream runoff and erosion during subsequent rainstorms. Hot pyroclastic flows and surges can also directly generate lahars by eroding and mixing with snow and ice on a volcano's flanks, thereby sending a sudden torrent of water surging down adjacent valleys (see case study from Nevado del Ruiz volcano, Colombia).”

"To envisage the scale of the deposits left by a super-eruption, we can consider this familiar (but unlikely) example. A super-eruption in Trafalgar Square, London, yielding 300 cubic kilometres of magma would produce enough volcanic (pyroclastic flow) deposits to bury all of Greater London to a depth of about 210 metres. A larger super-eruption (1000 cubic kilometres) would bury the same area to a depth of 700 metres. These thicknesses do not include extensive ash-fall deposits, which could cover an area greater than all of Europe."

"The [Pinatubo] climactic eruption produced 5 to 6 km3 of pyroclastic-flow deposits that partly buried valleys within 12 to 16 km of the volcano (W.E. Scott and others, this volume)."

Consequences: "Burial of all objects on ground and fires on a local scale, up to perhaps 50–80 kilometres from source volcano. Refugees – if pyroclastic flows were predicted, widespread evacuation would be required. This, depending on the area, could lead to a large number of persons requiring relocation. Tsunamis – if the volcano is near the coast, pyroclastic flows entering the sea could cause tsunamis. Around the island volcano of Krakatau in 1883, most of the 30,000 casualties were due to tsunamis sweeping ashore."

>> ===Lava Flows===

"Lava flows are streams of molten rock that pour or ooze from an erupting vent. Lava is erupted during either nonexplosive activity or explosive lava fountains. Lava flows destroy everything in their path, but most move slowly enough that people can move out of the way. The speed at which lava moves across the ground depends on several factors, including (1) type of lava erupted and its viscosity; (2) steepness of the ground over which it travels; (3) whether the lava flows as a broad sheet, through a confined channel, or down a lava tube; and (4) rate of lava production at the vent.

Fluid basalt flows can extend tens of kilometers from an erupting vent. The leading edges of basalt flows can travel as fast as 10 km/hour on steep slopes but they typically advance less than 1 km/hour on gentle slopes. But when basalt lava flows are confined within a channel or lava tube on a steep slope, the main body of the flow can reach velocities >30 km/hour.

Viscous andesite flows move only a few kilometers per hour and rarely extend more than 8 km from their vents. Viscous dacite and rhyolite flows often form steep-sided mounds called lava domes over an erupting vent. Lava domes often grow by the extrusion of many individual flows >30 m thick over a period of several months or years. Such flows will overlap one another and typically move less than a few meters per hour.

Everything in the path of an advancing lava flow will be knocked over, surrounded, or buried by lava, or ignited by the extremely hot temperature of lava. When lava erupts beneath a glacier or flows over snow and ice, meltwater from the ice and snow can result in far-reaching lahars. If lava enters a body of water or water enters a lava tube, the water may boil violently and cause an explosive shower of molten spatter over a wide area. Methane gas, produced as lava buries vegetation, can migrate in subsurface voids and explode when heated. Thick viscous lava flows, especially those that build a dome, can collapse to form fast-moving pyroclastic flows.

Deaths caused directly by lava flows are uncommon because most move slowly enough that people can move out the way easily and flows usually don't travel far from the vent. Death and injury can result when onlookers approach an advancing lava flow too closely or their retreat is cut off by other flows. Deaths attributed to lava flows are often due to related causes, such as explosions when lava interacts with water, the collapse of an active lava delta, asphyxiation due to accompanying toxic gases, pyroclastic flows from a collapsing dome, and lahars from meltwater.

Other natural phenomena such as hurricanes, tornadoes, tsunami, fires, and earthquakes often destroy buildings, agricultural crops, and homes, but the owner(s) can usually rebuild or repair structures and their businesses in the same location. Lava flows, however, can bury homes and agricultural land under tens of meters of hardened black rock; landmarks and property lines become obscured by a vast, new hummocky landscape. People are rarely able to use land buried by lava flows or sell it for more than a small fraction of its previous worth.

Because lava flows can completely block roads and highways that may serve as the only evacuation route for people threatened by an advancing flow, it is vital for communities that could be inundated with lava to develop emergency-response plans.

Basalt has the highest temperature of any lava, typically between about 1170-1100°C. The other lava types (andesite, dacite, and rhyolite) form cooler flows with temperatures between about 1000-800°C; some flows can still move slowly at temperatures as low as about 600°C."

>> ===Tephra, including volcanic ash===

“Were [Yellowstone or Long Valley] to go critical, they would blanket the western U.S. with many centimeters of ash in a matter of hours”

"The super-eruption of Toba volcano, Sumatra, some 74,000 years ago, ejected about 300 times more volcanic ash than the eruption of Tambora in Indonesia in 1815. Tambora’s eruption had significant impact on global climate, producing the “Year Without a Summer” (1816) when Lord Byron wrote his poem Darkness and Mary Shelley wrote Frankenstein. Unusually cool summers prevailed in the Northern Hemisphere for the following two years."

"It is easy to imagine that an eruption on the scale of Toba would have devastating global effects. A layer of ash estimated at 15 centimetres thick fell over the entire Indian sub-continent, with similar amounts over much of SE Asia. Most recently, Toba ash has been found in the South China Sea, implying that several centimetres also covered southern China. Just one centimetre of ash is enough to devastate agricultural activity, at least when it falls in the growing season. An eruption of this size would have catastrophic consequences. Many millions of lives throughout most of Asia would be threatened if Toba erupted today. The UK might not receive any ash fall directly, but it would be affected by the impact on global economic and political stability, as well as by worldwide climatic effects."

"The supereruption of Toba caused temperatures to drop globally by between 3 and 9 degrees Farenheit, as much as 18 degrees in some places, killed 80-90% of humans and destroyed as much as three-quarters of all vegetation in the Northern Hemisphere. (1) Substantial amounts of ash were distributed across southern Asia. In India, the ash was typically six inches thick, and at one site it reached an extraordinary depth of twenty feet (2)."

“For hundreds of kilometers around the eruption and for perhaps days or weeks, pale-gray ash would fall like clumps of snow. Within 200 kilometers of the caldera, most sunlight would be blocked out, so the sky at noon would look like that at dusk. Homes, people and animals would be buried, sometimes crushed. Even 300 kilometers away, the ash could be half a meter thick; mixed with rain, the weight would be plenty sufficient to collapse roofs. Less ash than that would knock out electrical power and relay stations. As little as a millimeter, which could well dust the ground halfway around the globe, would shut down airports and dramatically reduce agricultural production. Only gradually would rain (made acidic by volcanic gases) wash away the thick blanket of ash. And because volcanic rock and ash float, it would clog major waterways. Transportation along big rivers could grind to a halt.”

“The largest arc caldera-forming eruption in historic times was the A.D. 1815 eruption of Tambora (Indonesia). Approximately 100 km3 of tephra was produced, resulting in a VEI 7 classification—an order of magnitude smaller than a supervolcanic eruption.”

"The eruption of Mount Tambora in 1815 was minor compared to a supereruption, but serves as an example of the types of problems we could face. It ejected an estimated 36 cubic miles of ash and pumice, rising as much as 30 miles into the stratosphere. This cloud drifted around the world, visually affecting the atmosphere above both Europe and the USA. Many places suffered their worst winter on record. The winter at Yale University, in Connecticut USA, was 7°F below average. In Europe, food shortages were commonplace. Riots broke out, and armed groups looted farms. Ireland was worst hit, where the famine was believe to cause the spread of typhus, infecting 1.5 million people and killing 65,000. It was known as the Year Without Summer. In the last 600 years, only one year has been colder - 1601, following the eruption of a Peruvian volcano."

"[Tamboras] ash was responsible for some of the spectacular sunsets painted by Turner."

"Tephra is the fragmental material created by a volcanic eruption. Different types of tephra are determined by size - anything larger than 2.5 centimetres is called a "bomb", and ash is the smallest. Volcanic ash is quite different to the ash you get from burining something. Because it is a fragment of glass or rock, it has sharp edges - if you breathe it in, you will damage your lungs. These tiny pieces will combine with the moisture in your lungs and form a type of cement."

"Tephra is a general term for fragments of volcanic rock and lava regardless of size that are blasted into the air by explosions or carried upward by hot gases in eruption columns or lava fountains. Such fragments range in size from less than 2 mm (ash) to more than 1 m in diameter. Large-sized tephra typically falls back to the ground on or close to the volcano and progressively smaller fragments are carried away from the vent by wind. Volcanic ash, the smallest tephra fragments, can travel hundreds to thousands of kilometers downwind from a volcano."

Tephra consists of a wide range of rock particles (size, shape, density, and chemical composition), including combinations of pumice, glass shards, crystals from different types of minerals, and shattered rocks of all types (igneous, sedimentary, and metamorphic). A great variety of terms are used to describe the range of rock fragments thrown into the air by volcanoes. The terms classify the fragments according to size, shape, or the way in which they form and travel.

Ash usually covers a much larger area and disrupts the lives of far more people than the other more lethal types of volcano hazards. Unfortunately, the size of ash particles that fall to the ground and the thickness of ashfall downwind from an erupting volcano are difficult to predict in advance. Not only is there a wide range in the size of an eruption that might occur and the amount of tephra injected into the atmosphere, but the direction and strength of the prevailing wind can vary widely.

Volcanic ash is highly disruptive to economic activity because it covers just about everything, infiltrates most openings, and is highly abrasive. Airborne ash can obscure sunlight to cause temporary darkness and reduce visibility to zero. Ash is slippery, especially when wet; roads, highways, and airport runways may become impassable. Automobile and jet engines may stall from ash-clogged air filters and moving parts can be damaged from abrasion, including bearings, brakes, and transmissions."

"It is easy to imagine that an eruption on the scale of Toba would have devastating global effects. A layer of ash estimated at 15 centimetres thick fell over the entire Indian sub-continent, with similar amounts over much of SE Asia. Most recently, Toba ash has been found in the South China Sea, implying that several centimetres also covered southern China. Just one centimetre of ash is enough to devastate agricultural activity, at least when it falls in the growing season. An eruption of this size would have catastrophic consequences. Many millions of lives throughout most of Asia would be threatened if Toba erupted today. The UK might not receive any ash fall directly, but it would be affected by the impact on global economic and political stability, as well as by worldwide climatic effects."

"Tephra falls of varying character and volume occurred between April 2 and early September 1991, from eruptions of Mount Pinatubo. From April 2 to June 12, first phreatic explosions and later ash emissions related to emplacement of a lava dome produced mostly thin and fine-grained deposits over several hundred km2 west and south of the vent. A brief explosive eruption on the morning of June 12 deposited about 0.014 km3 of andesitic scoria, ash, and accidental lithic fragments southwest of the volcano (layer A). Several similar events over the next 2 days, followed by numerous pyroclastic-surge-producing explosions between the afternoon of June 14 and early afternoon of June 15, emplaced a 0.2 km3, laminated, mostly fine-grained ash-fall deposit (layer B) over broad areas around the volcano. The wide dispersal of layer B was induced by ash clouds convecting upward from pyroclastic surges that moved radially outward about 10 kilometers from the vent and the onset of low-altitude northerly to westerly winds as a tropical storm approached the area. The most voluminous deposit of the 1991 eruption sequence is a dacitic pumice-fall deposit (layer C) that was produced by the climactic eruption during the afternoon of June 15. A densely settled area of about 2,000 km2 was blanketed by 10 to 25 cm of rain-soaked tephra; 189 people were killed by collapsing buildings, and damage to utilities and agricultural lands was extensive. Most of Luzon and a roughly 4 million km2 area of the South China Sea and Southeast Asia were affected by tephra fall. The bulk volume of layer C probably lies between 3.4 and 4.4 km3, ranking it among the five largest of the 20th century. The climactic eruption also produced voluminous pyroclastic-flow deposits and a 2.5 km diameter caldera. Slowly diminishing ash emissions continued from several vents in the caldera for about 6 weeks following the climactic eruption and produced a fine-grained laminated tephra deposit (layer D), which has a bulk volume of about 0.2 km3."

"Tephra falls of changing character and volume occurred between April 2 and midsummer during the 1991 eruptions of Mount Pinatubo. These changes reflect the evolving eruptive behavior that built to a high-intensity plinian eruption and produced voluminous pyroclastic-flow deposits and a small caldera.

1. From April 2 to June 12, first phreatic explosions and later ash emissions related to emplacement of a lava dome produced mostly thin and fine-grained tephra-fall deposits that covered several hundred square kilometers west and south of the vent.

2. A brief explosive eruption on the morning of June 12 deposited about 14 million m3 of andesitic scoria, ash, and accidental lithic fragments southwest of the volcano (layer A). This event initiated a series of short-lived eruptions that led up to the climactic eruption.

3. Several events similar to that of the morning of June 12 occurred over the next 2 days, but each produced ejecta of smaller volume and finer grain size than layer A. These were followed by numerous pyroclastic-surge-producing eruptions between the afternoon of June 14 and early afternoon of June 15 (Hoblitt, Wolfe, and others, this volume). Together these events emplaced about 0.17 km3 of laminated, mostly fine-grained ash-fall deposits (layer B) over broad areas around the volcano. The wide dispersal of layer B was induced by ash clouds convecting upward from the pyroclastic surges that moved radially outward >=10 km from the vent, and by the onset of low-altitude northerly to westerly winds as a tropical storm approached the area.

4. The most voluminous fall deposit of the 1991 eruption sequence is a 3.4-4.4 km3 (bulk) dacitic pumice-fall deposit (layer C) that was produced by the climactic eruption during the afternoon of June 15. This volume probably ranks fifth among 20th century tephra-fall deposits. The climactic eruption also emplaced 5-6 km3 (bulk) of pumiceous pyroclastic-flow deposits and ended with formation of a 2.5 km wide caldera (W.E. Scott and others, this volume). Most of Luzon and a 3-4 million km2 area of the South China Sea and Southeast Asia were affected by tephra fall.

5. Grain-size analyses of samples of layer C display well known features of plinian tephra-fall deposits as distance from the vent increases, including decrease in median grain size, decrease in maximum pumice size, and improvement in sorting.

6. Component analyses show that pumice dominates in grain-size fractions coarser than 1 mm, whereas crystals dominate in finer fractions. Lithic fragments make up a few percent or less of each fraction.

7. The thickness and distribution of layer C was not well forecast in the initial hazard assessment because (1) tephra-fall deposits of past eruptions were not well preserved, as evidenced by the rapid erosion of layer C; (2) the eruption column reached a very high altitude (35 km) and mushroomed out widely in the stratosphere, even in the upwind direction (about 250 km from the vent), which helped to create a broad distribution; and (3) the coincidental passage of Typhoon (later tropical storm) Yunya to the northeast of the volcano caused a shift in low- and middle-tropospheric winds so that tephra was transported farther south than forecast.

8. Deposits of layer C typically have normal grading, which suggests that eruption intensity peaked early and then decreased until ending prior to cessation of pyroclastic-flow activity. Various lines of evidence imply that layer C was deposited in 3 to perhaps as much as 9 h.

9. Slowly diminishing ash emissions continued from several vents in the caldera for about 6 weeks following the climactic eruption and produced a fine-grained laminated tephra-fall deposit (layer D) that has a bulk volume of about 0.2 km3."



"Impacts of tephra fall are the most wide reaching among those directly resulting from explosive eruptions, as is illustrated by the Pinatubo experience with unquestionable clarity. Heavy tephra fall darkened central Luzon for most of the afternoon of June 15 during the climactic eruption. More than 30 cm of tephra-fall deposits accumulated close to the volcano, while a densely settled area of about 2,000 km2 received 10 to 25 cm. Fall deposits that were wetted by typhoon rains collapsed buildings and damaged public utilities and agricultural lands. Roof collapse accounted for 189 fatalities, or 61 percent of the total number recorded during the first 3.5 months after the eruption (Magboo and others, 1992). The estimated cost of damage to property is P10.62 billion (U.S. $400 million). The June 15 eruption itself affected about 216,000 families (National Disaster Coordinating Council, 1991). In addition, ash far from the volcano damaged aircraft (Casadevall and others, this volume) and ships."

"The [Pinatubo]... tephra-fall deposits were dispersed far and wide. Ash was carried westward across the South China Sea, where trace amounts fell in parts of Vietnam, Malaysia, and Borneo (Smithsonian Institution, 1991). The magnitude of this eruption earned it a place among the largest eruptions of this century (Self and others, this volume; W.E. Scott and others, this volume)."

Consequences: "Roof collapse in built-up areas – a local effect out to distances where ash fall is a few centimetres thick (tens of kilometres from the volcano). Exacerbated if rain occurs or ash fall is wet. Agriculture – devastation and disruption for at least a growing season over most of the area receiving ash fallout. Longer-term changes to soil composition. Drinking water – potential for both chemical and filtration/blockage problems associated with water supply. Aviation – risk to flying aircraft while ash still airborne (days to weeks); problems with landing and take-off until airports cleared. Power generation – effects of ash on hydroelectric and nuclear power plants unknown. Power distribution – electric pylons and power lines might be susceptible to ash loading and associated electrostatic effects. Possibly exacerbated if ash fall is wet."

>> ===Lahars===

"These occur in rivers and stream catchments after rainfall on fresh volcanic deposits. Possible damming of rivers, with ensuing breakout floods. Lahars caused the highest proportions of death and destruction associated with the Pinatubo eruption, but died down in the years after the activity."

"Lahar is an Indonesian term that describes a hot or cold mixture of water and rock fragments flowing down the slopes of a volcano and (or) river valleys. When moving, a lahar looks like a mass of wet concrete that carries rock debris ranging in size from clay to boulders more than 10 m in diameter. Lahars vary in size and speed. Small lahars less than a few meters wide and several centimeters deep may flow a few meters per second. Large lahars hundreds of meters wide and tens of meters deep can flow several tens of meters per second. As a lahar rushes downstream from a volcano, its size, speed, and the amount of water and rock debris it carries constantly change. The beginning surge of water and rock debris often erodes rocks and vegetation from the side of a volcano and along the river valley it enters. This initial flow can also incorporate water from melting snow and ice (if present) and the river it overruns. By eroding rock debris and incorporating additional water, lahars can easily grow to more than 10 times their initial size. But as a lahar moves farther away from a volcano, it will eventually begin to lose its heavy load of sediment and decrease in size.

Eruptions may trigger one or more lahars directly by quickly melting snow and ice on a volcano or ejecting water from a crater lake. More often, lahars are formed by intense rainfall during or after an eruption--rainwater can easily erode loose volcanic rock and soil on hillsides and in river valleys. Some of the largest lahars begin as landslides of saturated and hydrothermally altered rock on the flank of a volcano or adjacent hillslopes. Landslides are triggered by eruptions, earthquakes, precipitation, or the unceasing pull of gravity on the volcano.

Lahars almost always occur on or near stratovolcanoes because these volcanoes tend to erupt explosively and their tall, steep cones are either snow covered, topped with a crater lake, constructed of weakly consolidated rock debris that is easily eroded, or internally weakened by hot hydrothermal fluids. Lahars are also common from the snow- and ice-covered shield volcanoes in Iceland where eruptions of fluid basalt lava frequently occur beneath huge glaciers.

The scenarios listed below illustrate most of the mechanisms by which lahars are generated. For convenience, we've grouped the mechanisms according to whether a volcano is erupting, has erupted, or is quiet. Each mechanism is illustrated with one or more case studies.

Lahars racing down river valleys and spreading across flood plains tens of kilometers downstream from a volcano often cause serious economic and environmental damage. The direct impact of a lahar's turbulent flow front or from the boulders and logs carried by the lahar can easily crush, abrade, or shear off at ground level just about anything in the path of a lahar. Even if not crushed or carried away by the force of a lahar, buildings and valuable land may become partially or completely buried by one or more cement-like layers of rock debris. By destroying bridges and key roads, lahars can also trap people in areas vulnerable to other hazardous volcanic activity, especially if the lahars leave deposits that are too deep, too soft, or too hot to cross.

After a volcanic eruption, the erosion of new loose volcanic deposits in the headwaters of rivers can lead to severe flooding and extremely high rates of sedimentation in areas far downstream from a volcano. Over a period of weeks to years, post-eruption lahars and high-sediment discharges triggered by intense rainfall frequently deposit rock debris that can bury entire towns and valuable agricultural land. Such lahar deposits may also block tributary stream valleys. As the area behind the blockage fills with water, areas upstream become inundated. If the lake is large enough and it eventually overtops or breaks through the lahar blockage, a sudden flood or a lahar may bury even more communities and valuable property downstream from the tributary."

[|Lahar-Detection System]

>> ===Tsunamis===

"The famous Krakatoa eruption of 1883 caused a series of tsunamis, up to 100 feet in height, killing tens of thousands of people. The final explosion was defeaning, and was heard 3,000 miles away."

> ==Aftermath==

>> ===Volcanic Gases===

"The last time Iceland had a colossal eruption was in 1783. Laki, a fissure close to the Grimsvotn volcano, burst open and threw up fountains of lava and clouds of ash for eight months. The poisonous sulphur dioxide gas killed over half of Iceland's livestock population and led to a famine that wiped out about a quarter of the country's population. Meanwhile, as the cloud blew south it wreaked havoc over Europe, too. "This outpouring of sulphur dioxide during unusual weather conditions caused a thick haze to spread across western Europe, resulting in thousands of deaths throughout 1783 and the winter of 1784," says Jerram. The fog was so thick that boats across Europe were forced to stay in port. Further afield, the effects were also severe. "There is evidence that Laki may have caused the failure of the rice harvest in Japan that year, and weakened the African and Indian monsoon circulation," Thordarson says. On the explosivity index, Laki is judged to have been a six - the kind of volcano that occurs once every century, on average."

"As to non-explosive eruptions involving the outpouring of copious amounts of lava, the most likely place for such an eruption today is Iceland; and so this kind of eruption is of particular interest to Europe. The last one began in 1783 when the Laki fissure disgorged about 15 cubic kilometres of lava over eight months (see p.5). Enormous quantities of sulphur dioxide were released and caused climatic anomalies in Europe and North America, including a dry acid fog over Europe, and severe crop failures. Many of the livestock in Iceland died from poisoning by halogen gases (chlorine and fluorine). As a consequence about one third of the Icelandic people died from famine. Related food shortages in France may even have been one of the factors that eventually triggered the French Revolution. Eruptions of this scale seem to take place on Iceland on average every 1000 years. The next large lava eruption on Iceland will not be of super-eruption scale by the definition given here, but it could be environmentally and economically devastating for Europe."

"...the severity of environmental effects is not simply determined by the amount of erupted material. The mass of erupted gas, which is related to the mass of magma, is crucial. It is now known that the most important factor in determining the impact of eruptions on global climate is the amount of sulphur and halogen gases (chlorine and fluorine) erupted. Not all volcanoes erupt magmas with large amounts of sulphur or halogen gas. Therefore a critical scientific issue is the mass of these key gases released, which is unfortunately not yet well constrained."

“Investigators have reason to believe that other consequences, arising from the great volumes of problematic gas expelled into the upper atmosphere, would also transpire and could persist for many years.”

“Of the varied gases that make up any volcanic eruption, sulfur dioxide (SO2) causes the strongest effect on the environment; it reacts with oxygen and water to produce tiny droplets of sulfuric acid (H2SO4). These droplets are the main sun-blocking source of the dramatic climatic cooling that would grip the planet in the wake of a supereruption. Knowing that the planet's hydrological cycle takes months or years to fully wash away the acid droplets, many researchers made apocalyptic estimates of “volcanic winters” lasting decades, if not centuries. But in recent years other investigators have uncovered evidence that drastically reduces that calculation.”

“...a new method developed in the past five years for studying the composition of the oxygen atoms in the volcanic acid rain is revealing an entirely different, alarming sign about the long-term effects of sulfur dioxide in the atmosphere. For SO2 to become H2SO4, it must be oxidized—in other words, it must acquire two oxygen atoms from other compounds already existing in the atmosphere. … The oxygen 17 excess and other chemical patterns that we found in sulfate from the Yellowstone and Long Valley ash samples thus implied that significant amounts of stratospheric ozone were used up in reactions with gas from the supereruptions in those regions. Other researchers studying the acid layers in Antarctica have demonstrated that those events, too, probably eroded stratospheric ozone. It begins to look as if supervolcano emissions eat holes in the ozone layer for an even longer period than they take to cool the climate. / This loss of protective ozone would be expected to result in an increased amount of dangerous ultraviolet radiation reaching the earth's surface and thus in a rise in genetic damage caused by rays. The magnitude and length of the potential ozone destruction are still being debated. Space observations have revealed a 3 to 8 percent depletion of the ozone layer following the 1991 eruption of Mount Pinatubo in the Philippines. But what would happen after an event 100 times larger? Simple arithmetic does not solve the problem, because the details of atmospheric oxidation reactions are extremely complex and not fully understood.”

"Magma contains dissolved gases that are released into the atmosphere during eruptions. Gases are also released from magma that either remains below ground (for example, as an intrusion) or is rising toward the surface. In such cases, gases may escape continuously into the atmosphere from the soil, volcanic vents, fumaroles, and hydrothermal systems.

At high pressures deep beneath the earth's surface, volcanic gases are dissolved in molten rock. But as magma rises toward the surface where the pressure is lower, gases held in the melt begin to form tiny bubbles. The increasing volume taken up by gas bubbles makes the magma less dense than the surrounding rock, which may allow the magma to continue its upward journey. Closer to the surface, the bubbles increase in number and size so that the gas volume may exceed the melt volume in the magma, creating a magma foam. The rapidly expanding gas bubbles of the foam can lead to explosive eruptions in which the melt is fragmented into pieces of volcanic rock, known as tephra. If the molten rock is not fragmented by explosive activity, a lava flow will be generated.

Together with the tephra and entrained air, volcanic gases can rise tens of kilometers into Earth's atmosphere during large explosive eruptions. Once airborne, the prevailing winds may blow the eruption cloud hundreds to thousands of kilometers from a volcano. The gases spread from an erupting vent primarily as acid aerosols (tiny acid droplets), compounds attached to tephra particles, and microscopic salt particles.

Volcanic gases undergo a tremendous increase in volume when magma rises to the Earth's surface and erupts. For example, consider what happens if one cubic meter of 900°C rhyolite magma containing five percent by weight of dissolved water were suddenly brought from depth to the surface. The one cubic meter of magma now would occupy a volume of 670 m3 as a mixture of water vapor and magma at atmospheric pressure (Sparks et. al., 1997)! The one meter cube at depth would increase to 8.75 m on each side at the surface. Such enormous expansion of volcanic gases, primarily water, is the main driving force of explosive eruptions.

The most abundant gas typically released into the atmosphere from volcanic systems is water vapor (H2O), followed by carbon dioxide (CO2) and sulfur dioxide (SO2). Volcanoes also release smaller amounts of others gases, including hydrogen sulfide (H2S), hydrogen (H2), carbon monoxide (CO), hydrogen chloride (HCL), hydrogen fluoride (HF), and helium (He).



The volcanic gases that pose the greatest potential hazard to people, animals, agriculture, and property are sulfur dioxide, carbon dioxide, and hydrogen fluoride. Locally, sulfur dioxide gas can lead to acid rain and air pollution downwind from a volcano. Globally, large explosive eruptions that inject a tremendous volume aerosols into the stratosphere can lead to lower surface temperatures and promote depletion of the Earth's ozone layer. Because carbon dioxide gas is heavier than air, the gas may flow into in low-lying areas and collect in the soil. The concentration of carbon dioxide gas in these areas can be lethal to people, animals, and vegetation. A few historic eruptions have released sufficient fluorine-compounds to deform or kill animals that grazed on vegetation coated with volcanic ash; fluorine compounds tend to become concentrated on fine-grained ash particles, which can be ingested by animals.


 * Sulfur dioxide (SO2)**

The effects of SO2 on people and the environment vary widely depending on (1) the amount of gas a volcano emits into the atmosphere; (2) whether the gas is injected into the troposphere or stratosphere; and (3) the regional or global wind and weather pattern that disperses the gas. Sulfur dioxide (SO2) is a colorless gas with a pungent odor that irritates skin and the tissues and mucous membranes of the eyes, nose, and throat. Sulfur dioxide chiefly affects upper respiratory tract and bronchi. The World Health Organization recommends a concentration of no greater than 0.5 ppm over 24 hours for maximum exposure. A concentration of 6-12 ppm can cause immediate irritation of the nose and throat; 20 ppm can cause eye irritation; 10,000 ppm will irritate moist skin within minutes.

Emission rates of SO2 from an active volcano range from <20 tonnes/day to >10 million tonnes/day according to the style of volcanic activity and type and volume of magma involved. For example, the large explosive eruption of Mount Pinatubo on 15 June 1991 expelled 3-5 km3 of dacite magma and injected about 20 million metric tons of SO2 into the stratosphere. The sulfur aerosols resulted in a 0.5-0.6°C cooling of the Earth's surface in the Northern Hemisphere. The sulfate aerosols also accelerated chemical reactions that, together with the increased stratospheric chlorine levels from human-made chlorofluorocarbon (CFC) pollution, destroyed ozone and led to some of the lowest ozone levels ever observed in the atmosphere.

At Kilauea Volcano, the recent effusive eruption of about 0.0005 km3/day (500,000 m3) of basalt magma releases about 2,000 tonnes of SO2 into the lower troposphere. Downwind from the vent, acid rain and air pollution is a persistent health problem when the volcano is erupting."

"Measurements of the Pinatubo sulphur dioxide injection by satellite-borne instruments showed that the aerosol plume encircled the globe in only three weeks, and then slowly dispersed to cover much of the Earth in the following two years. Eventually the circulation pattern of the upper atmosphere causes the aerosol particles to fall back to the surface in the polar regions. Stratospheric aerosols absorb heat so that, on average, the upper atmosphere is heated and the lower atmosphere is cooled significantly. However, the response of the atmosphere is complex, so that there are areas of both highly anomalous heating and cooling in the few years following an eruption."

"The Toba eruption has been dated by various methods K/Ar method at 73,500 ± 3500 yr BP (Chesner et al., 1991). The Toba ash layer occurs in deep-sea cores from the Indian Ocean and South China Sea (Huang et al., 2001; Shultz et al., 2002; Song et al., 2000). The widespread ash layer has a dense rock equivalent volume (DRE) of approximately 800km3 (Chesner etal., 1991).The pyroclastic flow deposits on Sumatra have a volume of approximately 2000 km3 DRE (Chesner etal., 1991; Rose and Chesner, 1990), for a total eruption volume of approximately 2800 km3 (DRE). Woods and Wohletz (1991) estimated Toba eruption cloud heights of 32 ± 5km, and the duration of continuous fallout of Toba ash over the Indian Ocean has been estimated at two weeks or less (Ledbetter and Sparks, 1979)...Based on studies of the sulphur content of the Toba deposits, Rose and Chesner (1990) estimated that approximately 3 x 10^15 g of H2S/SO2 (equivalent to ~ 1 x 10^16 g of H2SO4 aerosols) could have been released from the erupted magma. The amounts of fine ash and sulphuric acid aerosols that could have been generated by Toba was estimated independently using data from smaller historical rhyolitic eruptions (Rampino and Self, 1992). By this simple extrapolation, the Toba super-eruption could have produced up to 2 x 10^16 g of fine (<2 ц) dust and approximately 1.5 x 10^15 g of sulphuric acid aerosols."

//SO2 effects Earth's surface temperature Global cooling and ozone depletion//

"Measurements from recent eruptions such as Mount St. Helens, Washington (1980), El Chichon, Mexico (1982), and Mount Pinatubo, Philippines (1991), clearly show the importance of sulfur aerosols in modifying climate, warming the stratosphere, and cooling the troposphere. Research has also shown that the liquid drops of sulfuric acid promote the destruction of the Earth's ozone layer.


 * Hydrogen sulfide (H2S)**

Hydrogen sulfide (H2S) is a colorless, flammable gas with a strong offensive odor. It is sometimes referred to as sewer gas. At low concentrations it can irritate the eyes and acts as a depressant; at high concentrations it can cause irritation of the upper respiratory tract and, during long exposure, pulmonary edema. A 30-minute exposure to 500 ppm results in headache, dizziness, excitement, staggering gait, and diarrhea, followed sometimes by bronchitis or bronchopneumonia.


 * Carbon dioxide (CO2)**

Volcanoes release more than 130 million tonnes of CO2 into the atmosphere every year. This colorless, odorless gas usually does not pose a direct hazard to life because it typically becomes diluted to low concentrations very quickly whether it is released continuously from the ground or during episodic eruptions. But in certain circumstances, CO2 may become concentrated at levels lethal to people and animals. Carbon dioxide gas is heavier than air and the gas can flow into in low-lying areas; breathing air with more than 30% CO2 can quickly induce unconsciousness and cause death. In volcanic or other areas where CO2 emissions occur, it is important to avoid small depressions and low areas that might be CO2 traps. The boundary between air and lethal gas can be extremely sharp; even a single step upslope may be adequate to escape death.

//CO2 trapped in depressions can be lethal to people and animals//

Air with 5% CO2 causes perceptible increased respiration; 6-10% results in shortness of breath, headaches, dizziness, sweating, and general restlessness; 10-15% causes impaired coordination and abrupt muscle contractions; 20-30% causes loss of consciousness and convulsions; over 30% can cause death (Hathaway et. al., 1991).


 * Hydrogen Chloride (HCl)**

Chlorine gas is emitted from volcanoes in the form of hydrochloric acid (HCl). Exposure to the gas irritates mucous membranes of the eyes and respiratory tract. Concentrations over 35 ppm cause irritation of the throat after short exposure; >100 ppm results in pulmonary edema, and often laryngeal spasm. It also causes acid rain downwind from volcanoes because HCl is extremely soluble in condensing water droplets and it is a very "strong acid" (it dissociates extensively to give H+ ions in the droplets).


 * Hydrogen Fluoride (HF)**

Fluorine is a pale yellow gas that attaches to fine ash particles, coats grass, and pollutes streams and lakes. Exposure to this powerful caustic irritant can cause conjunctivitis, skin irritation, bone degeneration and mottling of teeth. Excess fluorine results in a significant cause of death and injury in livestock during ash eruptions. Even in areas that receive just a millimeter of ash, poisoning can occur where the fluorine content of dried grass exceeds 250 ppm. Animals that eat grass coated with fluorine-tainted ash are poisoned. Small amounts of fluorine can be beneficial, but excess fluorine causes fluorosis, an affliction that eventually kills animals by destroying their bones. It also promotes acid rain effects downwind of volcanoes, like HCl.


 * Secondary Gas Emissions**

Another type of gas release occurs when lava flows reach the ocean. Extreme heat from molten lava boils and vaporizes seawater, leading to a series of chemical reactions. The boiling and reactions produce a large white plume, locally known as lava haze or laze, containing a mixture of hydrochloric acid and concentrated seawater.

//Laze plumes are very acidic//

Extreme heat from lava entering the sea rapidly boils and vaporizes seawater, leading to a series of chemical reactions. The boiling and reactions produce a large white plume, locally known as lava haze or laze, which contains a mixture of hydrochloric acid (HCl) and concentrated seawater. This is a short-lived local phenomenon that only affects people or vegetation directly under the plume.

The hydrochloric acid (HCl) comes from the breakdown of seawater-derived chlorides during sudden boiling. Because the lava is largely degassed by the time it reaches the sea, any HCL coming from it is insignificant by comparison. Analyzed samples of the plume show that is is a brine with a salinity of about 2.3 times that of seawater and a pH of 1.5-2.0.

White acid-rich steam plume rises from lava flows entering the sea Key seawater chloride breakdown reactions that produce HCl gas


 * MgCl2 (sea salt) + H2O (steam) = MgO (periclase) + 2HCl (HCl gas)


 * 2 NaCl (sea salt) + H2O (steam) = Na2O (sodium oxide) + 2 HCL (HCl gas)


 * CaCl2 (sea salt) + H2O (steam) = CaO (lime) + 2 HCL (HCl gas)

Avoid standing beneath a laze plume. Dense laze plumes...contain as much as 10-15 parts per million of hydrochloric acid. These values drop off sharply as the plume moves away from the lava entry areas. During along-shore or on-shore winds, this plume produces acid rain that may fall on people and land along the coast. This rain (pH 1.5 to 2), often more acidic that lime juice or stomach acid, is very corrosive to the skin and clothing. Visitors to the lava entry areas should avoid standing directly in, under, or downwind of the laze plume."

"Dry-fog and acid aerosol air pollution – a Laki-type dry fog in the lower atmosphere (composed of sulphur dioxide gas and sulphuric acid aerosols) could induce respiratory illness, as could fine ash (< 10 microns) and other minerals in the ash. Such clouds can attain complete coverage within a hemisphere. Chemical etching effects of aerosol particles on aircraft engines and instrumentation is a little understood aspect."

>>> ====**Acid Rain**====

"Acid rain describes any form of precipitation with high levels of nitric and sulfuric acids. It can also occur in the form of snow, fog, and tiny bits of dry material that settle to Earth.

Rotting vegetation and erupting volcanoes release some chemicals that can cause acid rain, but most acid rain falls because of human activities. The biggest culprit is the burning of fossil fuels by coal-burning power plants, factories, and automobiles.

When humans burn fossil fuels, sulfur dioxide (SO2) and nitrogen oxides (NOx) are released into the atmosphere. These chemical gases react with water, oxygen, and other substances to form mild solutions of sulfuric and nitric acid. Winds may spread these acidic solutions across the atmosphere and over hundreds of miles. When acid rain reaches Earth, it flows across the surface in runoff water, enters water systems, and sinks into the soil.

Acid rain has many ecological effects, but none is greater than its impact on lakes, streams, wetlands, and other aquatic environments. Acid rain makes waters acidic and causes them to absorb the aluminum that makes its way from soil into lakes and streams. This combination makes waters toxic to crayfish, clams, fish, and other aquatic animals.

Some species can tolerate acidic waters better than others. However, in an interconnected ecosystem, what impacts some species eventually impacts many more throughout the food chain—including non-aquatic species such as birds.

Acid rain also damages forests, especially those at higher elevations. It robs the soil of essential nutrients and releases aluminum in the soil, which makes it hard for trees to take up water. Trees' leaves and needles are also harmed by acids.

The effects of acid rain, combined with other environmental stressors, leave trees and plants less able to withstand cold temperatures, insects, and disease. The pollutants may also inhibit trees' ability to reproduce. Some soils are better able to neutralize acids than others. In areas where the soil's "buffering capacity" is low, the harmful effects of acid rain are much greater.

The only way to fight acid rain is by curbing the release of the pollutants that cause it. This means burning fewer fossil fuels. Many governments have tried to curb emissions by cleaning up industry smokestacks and promoting alternative fuel sources. These efforts have met with mixed results. But even if acid rain could be stopped today, it would still take many years for its harmful effects to disappear.

Individuals can also help prevent acid rain by conserving energy. The less electricity people use in their homes, the fewer chemicals power plants will emit. Vehicles are also major fossil fuel users, so drivers can reduce emissions by using public transportation, carpooling, biking, or simply walking wherever possible."


 * What is Acid Rain and What Causes It?**

"'Acid rain' is a broad term used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition, which has two parts: wet and dry.

Wet deposition refers to acidic rain, fog, and snow. As this acidic water flows over and through the ground, it affects a variety of plants and animals. The strength of the effects depend on many factors, including how acidic the water is, the chemistry and buffering capacity of the soils involved, and the types of fish, trees, and other living things that rely on the water.

Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition. The wind blows these acidic particles and gases onto buildings, cars, homes, and trees. Dry deposited gases and particles can also be washed from trees and other surfaces by rainstorms. When that happens, the runoff water adds those acids to the acid rain, making the combination more acidic than the falling rain alone.

Prevailing winds blow the compounds that cause both wet and dry acid deposition across state and national borders, and sometimes over hundreds of miles. Scientists discovered, and have confirmed, that sulfur dioxide (SO2) and nitrogen oxides (NOx) are the primary causes of acid rain. In the US, About 2/3 of all SO2 and 1/4 of all NOx comes from electric power generation that relies on burning fossil fuels like coal.

Acid rain occurs when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. Sunlight increases the rate of most of these reactions. The result is a mild solution of sulfuric acid and nitric acid.

//How Do We Measure Acid Rain?//

Acid rain is measured using a scale called "pH." The lower a substance's pH, the more acidic it is. Pure water has a pH of 7.0. Normal rain is slightly acidic because carbon dioxide dissolves into it, so it has a pH of about 5.5. As of the year 2000, the most acidic rain falling in the US has a pH of about 4.3.

Acid rain's pH, and the chemicals that cause acid rain, are monitored by two networks, both supported by EPA. The National Atmospheric Deposition Program measures wet deposition, and its Web site features maps of rainfall pH (follow the link to the isopleth maps) and other important precipitation chemistry measurements.

The Clean Air Status and Trends Network (CASTNET) measures dry deposition. Its web site features information about the data it collects, the measuring sites, and the kinds of equipment it uses.

//Effects of Acid Rain//

Acid rain causes acidification of lakes and streams and contributes to damage of trees at high elevations (for example, red spruce trees above 2,000 feet) and many sensitive forest soils. In addition, acid rain accelerates the decay of building materials and paints, including irreplaceable buildings, statues, and sculptures that are part of our nation's cultural heritage. Prior to falling to the earth, SO2 and NOx gases and their particulate matter derivatives, sulfates and nitrates, contribute to visibility degradation and harm public health.

//What Society Can Do About Acid Deposition//

There are several ways to reduce acid deposition, more properly called acid deposition, ranging from societal changes to individual action.

//Understand acid deposition's causes and effects//

To understand acid deposition's causes and effects and track changes in the environment, scientists from EPA, state governments, and academic study acidification processes. They collect air and water samples and measure them for various characteristics like pH and chemical composition, and they research the effects of acid deposition on human-made materials such as marble and bronze. Finally, scientists work to understand the effects of sulfur dioxide (SO2) and nitrogen oxides (NOx) - the pollutants that cause acid deposition and fine particles - on human health.

To solve the acid rain problem, people need to understand how acid rain causes damage to the environment. They also need to understand what changes could be made to the air pollution sources that cause the problem. The answers to these questions help leaders make better decisions about how to control air pollution and therefore how to reduce - or even eliminate - acid rain. Since there are many solutions to the acid rain problem, leaders have a choice of which options or combination of options are best. The next section describes some of the steps that can be taken to reduce, or even eliminate, the acid deposition problem.

//Restore a damaged environment//

Acid deposition penetrates deeply into the fabric of an ecosystem, changing the chemistry of the soil as well as the chemistry of the streams and narrowing, sometimes to nothing, the space where certain plants and animals can survive. Because there are so many changes, it takes many years for ecosystems to recover from acid deposition, even after emissions are reduced and the rain becomes normal again. For example, while the visibility might improve within days, and small or episodic chemical changes in streams improve within months, chronically acidified lakes, streams, forests, and soils can take years to decades or even centuries (in the case of soils) to heal.

However, there are some things that people do to bring back lakes and streams more quickly. Limestone or lime (a naturally-occurring basic compound) can be added to acidic lakes to "cancel out" the acidity. This process, called liming, has been used extensively in Norway and Sweden but is not used very often in the United States. Liming tends to be expensive, has to be done repeatedly to keep the water from returning to its acidic condition, and is considered a short-term remedy in only specific areas rather than an effort to reduce or prevent pollution. Furthermore, it does not solve the broader problems of changes in soil chemistry and forest health in the watershed, and does nothing to address visibility reductions, materials damage, and risk to human health. However, liming does often permit fish to remain in a lake, so it allows the native population to survive in place until emissions reductions reduce the amount of acid deposition in the area."

[|Acid Rain]

>>> ====**Climate Change**====

"Our results challenge this conclusion because they show that the Toba eruption led to prolonged drought and deforestation in India, probably lasting for 1000– 2000 years. Cooling arising from the Toba super-eruption is consid- ered responsible for the extreme cold of ice core stadial 20 (Zielinski et al., 1996) and is supported by our work. The precise magnitude and duration of the Toba-induced cooling in other regions of the world is still not well known, because their environmental records are not stratified with clear markers of the 73 ka Toba eruption. However, cores from three large, deep lakes in tropical Africa (Lakes Malawi, Tanganyika and Bosumtwi) have unusual depositional events at ∼73 ka, reflecting apparently synchronous abrupt drops in lake levels (Scholz et al., 2007). This is consistent with a severe global envi- ronmental impact for the Toba-induced cooling."

"Rousseau and Kukla (2000) noted rapid monsoon retreat in China at the S1/L1 boundary of the long loess- palaeosol sequence of the Loess Plateau, and suggested that the most likely cause was sudden rearrangement of the [|oceanic conveyor belt], perhaps triggered by the Toba eruption. The cooling effects of historic eruptions are known to involve the generation of highly reflective low-level clouds produced by sulfate aerosols and of dust veils scattering solar radiation (Rampino and Self, 1982; Rampino et al., 1985; Sadler and Grattan, 1999) and vary spatially over time (Kelly et al., 1996). However, such cooling is short-lived, lasting only several years, after which the aerosols and dust particles are scavenged by falling rain. The cooling generated by the Toba sulfates (Zielinski et al., 1996) may have been accentuated in high latitudes through positive feedback effects related to increased albedo from persistent snow cover at high latitudes (Rampino and Self, 1993; Zielinski et al., 1996; Kelly et al., 1996; Jones et al., 2005)."

"The cycle analysed by Lang et al. (1999) shows a very rapid 16 °C change in temperature at about the time of the Toba eruption, but in the absence of direct geochemical evidence we cannot be certain that it reflects the climatic impact of the Toba eruption. Millennial- scale variation in δ18O of atmospheric O2 in the North Greenland ice core is correlated with evaporative enrichment in transpired plant leaf water, and an abrupt increase in percentages of semi-desert plant biomass in Mediterranean Sea core ODP 976 at ∼74 ka (Genty et al., 2005; Landais et al., 2007). If the Toba eruption did indeed coincide with the onset of the very cold event just after interstadial 20, as seems probable (Zielinski et al., 1996), then the Toba eruption may have provided the catalyst for the prolonged cooling and drying that followed. In any event, the impact on prehistoric human societies would have been profound, as indicated by the genetic evidence (Harpending et al., 1993; Ambrose, 1998; Forster, 2004)."

"Our new carbon isotope evidence from fossil soils found immediately beneath and above the Toba ash in central India demonstrates a major isochronous change in vegetation from forest before the eruption to open woodland or grassland thereafter. Terrestrial pollen spectra from a marine core collected from the Bay of Bengal support the terrestrial isotopic evidence indicating initially cooler temperatures followed by decreased tree cover and prolonged drought for at least a millennium following the Toba eruption. These terrestrial and marine archives of climatic change following the Toba super-eruption provide support for the hypothesis that severe environmental degradation could have been responsible for large mammal extinctions in southeast Asia and genetic bottlenecks in humans and other species that occurred in Africa and southeast Asia at this time."

"It is not clear how the understanding and observations of relatively small historic eruptions, like Krakatau and Pinatubo, can be extrapolated to super-eruptions. It can safely be assumed that their effects will be more severe, but the Earth’s climate system is not well enough understood for us to be very confident in detailed predictions. In principle, putting twice as much aerosol in the stratosphere should double the predicted climatic effect. But climate systems are complex, with important feedback processes. Thus the consequences of very much larger injections of volcanic gas cannot be forecast with much confidence.

It is also possible that other components (dust and non-sulphurous gases) may have a much more significant role when injected into the stratosphere in much larger amounts. As in many situations with global climate there are forcing factors that might inhibit and forcing factors that might magnify the effects of a super-volcano eruption on climate."

"The exceptional magnitude of the Toba eruption makes it a natural target in the studies of large volcanic events preserved in polar ice cores. Work on the GISP2 ice core from Summit, Greenland, revealed an approximately 6-year long period of enhanced volcanic sulphate dated at 71,100 ± 5000 years ago identified with the Toba eruption (Zielinski et al., 1996a, 1996b). The magnitude of this sulphate signal is the largest in the entire 110,000 years of the GISP2 record.

Zielinski and others (1996a) estimated that the total atmospheric loading of H2SO4 for the approximately 6-year period of the ice-core peak ranged from approximately 0.7 to 4.4 x 10^15 g, in general agreement with the above estimates derived from volcano logical techniques and scaling from smaller eruptions (Rampino and Self, 1992,1993a; Rose and Chesner, 1990). Estimates of aerosol loadings range from approximately 150 to 1000 Mt per year, over the approximately 6-year period of the ice-core peak.

The SO^~ signal identified with Toba coincides with the beginning of an approximately 1000-year cooling event seen in the ice-core record between brief warm periods (interstadials), but is separated from the most recent major approximately 9000-year glacial period by the approximately 2000-year-long warmer period. A similar cool pulse between interstadials is seen in the pollen record of the Grande Pile in northeastern France, dated as approximately 70,000 years BP (Woillard and Mook, 1982).

Thus, the ice-core evidence suggests that the Toba signal occurred during the transition from a warm interglacial climate and was preceded and followed by abrupt climate oscillations that preceded the start of the most recent major early glaciation (Zielinski et al., 1996a, 1996b)."

"Several of the largest volcanic eruptions of the last few hundred years (Tambora, 1815; Krakatau*, 1883; Pinatubo, 1991) have caused major climatic anomalies in the two to three years after the eruption by creating a cloud of sulphuric acid droplets in the upper atmosphere. These droplets absorb and reflect sunlight, and absorb heat from the Earth, warming the upper atmosphere and cooling the lower atmosphere. The global climate system is disturbed, resulting in pronounced, anomalous warming and cooling of different parts of the Earth at different times.

Super-eruptions, however, are hundreds of times larger than these recent events and their global effects are likely to be much more severe. An area the size of North America or Europe could be devastated, and pronounced deterioration of global climate would be expected for a few years following the eruption. Such events could result in the ruin of world agriculture, severe disruption of food supplies, and mass starvation. The effects could be sufficiently severe to threaten the fabric of civilisation."

"Climate change – dominantly lower temperatures for a few years after the eruption might change agricultural yields. Some areas may undergo warming, and there might be short-term, very warm spells that could also affect growing crops. Changes in rainfall patterns may influence liablilty to flooding in certain areas."


 * Volcanic Gases and Climate Change Overview**

"Volcanoes can impact climate change. During major explosive eruptions huge amounts of volcanic gas, aerosol droplets, and ash are injected into the stratosphere. Injected ash falls rapidly from the stratosphere -- most of it is removed within several days to weeks -- and has little impact on climate change. But volcanic gases like sulfur dioxide can cause global cooling, while volcanic carbon dioxide, a greenhouse gas, has the potential to promote global warming.

The most significant climate impacts from volcanic injections into the stratosphere come from the conversion of sulfur dioxide to sulfuric acid, which condenses rapidly in the stratosphere to form fine sulfate aerosols. The aerosols increase the reflection of radiation from the Sun back into space, cooling the Earth's lower atmosphere or troposphere. Several eruptions during the past century have caused a decline in the average temperature at the Earth's surface of up to half a degree (Fahrenheit scale) for periods of one to three years. The climactic eruption of Mount Pinatubo on June 15, 1991, was one of the largest eruptions of the twentieth century and injected a 20-million ton (metric scale) sulfur dioxide cloud into the stratosphere at an altitude of more than 20 miles. The Pinatubo cloud was the largest sulfur dioxide cloud ever observed in the stratosphere since the beginning of such observations by satellites in 1978. It caused what is believed to be the largest aerosol disturbance of the stratosphere in the twentieth century, though probably smaller than the disturbances from eruptions of Krakatau in 1883 and Tambora in 1815. Consequently, it was a standout in its climate impact and cooled the Earth's surface for three years following the eruption, by as much as 1.3 degrees at the height of the impact. Sulfur dioxide from the large 1783-1784 Laki fissure eruption in Iceland caused regional cooling of Europe and North America by similar amounts for similar periods of time.

While sulfur dioxide released in contemporary volcanic eruptions has occasionally caused detectable global cooling of the lower atmosphere, the carbon dioxide released in contemporary volcanic eruptions has never caused detectable global warming of the atmosphere. This is probably because the amounts of carbon dioxide released in contemporary volcanism have not been of sufficient magnitude to produce detectable global warming. For example, all studies to date of global volcanic carbon dioxide emissions indicate that present-day subaerial and submarine volcanoes release less than a percent of the carbon dioxide released currently by human activities. While it has been proposed that intense volcanic release of carbon dioxide in the deep geologic past did cause global warming, and possibly some mass extinctions, this is a topic of scientific debate at present."


 * Volcanic Sulfur Aerosols Affect Climate and the Earth's Ozone Layer**

"Some of the largest events occured in continental hotspot ar- eas where extensional tectonics and thick continental crust lead to large-volume magma chambers of silicic composition (Smith and Luedke 1984, Smith and Braile 1994). The greatest explo- sive eruption in the past few hundred thousand years was the Toba (Sumatra) event of ∼73,500 years ago (Chesner et al. 1991, Rampino and Self 1992, 1993). This event produced at least 2,800 km3 of magma (pyroclastic flow deposits, pumice fall, and ash) and is estimated to have created from 1,000 to 10,000 Mt of stratospheric dust and sulfuric acid aerosols (Chesner et al. 1991, Rampino and Self 1992, Zielinski et al. 1996a). Extrapolation of the data of Pyle et al. (1996) to VEI 8 eruptions gives about 1000 Mt of SO2 release, which would be converted to aerosols in the stratosphere. The Toba aerosols apparently persisted for up to 6 years in the upper atmosphere (Rampino and Self 1992, 1993, Zielinski et al. 1996a).

Based on scaling up from smaller eruptions and computer models, stratospheric aerosol loading of ∼1000 Mt is predicted to have caused a “volcanic winter,” with a global cooling of 3 to 5◦C for several years, and regional coolings up to 15◦C (Rampino and Self 1992, 1993) (see Fig. 1; Table I). Such a cooling is estimated to have drastically affected tropical and temperate vegetation and ecosystems (Rampino and Ambrose 2000). All above-ground tropical vegetation would have been killed by sudden hard freezes, and a 50% die-off of temperate forests is predicted from hard freezes during the growing sea- son (Rampino and Ambrose 2000, Sagan and Turco 1990)."

“In 1996 investigators studying ice cores from Greenland and Antarctica found the sulfuric acid peak that followed the supereruption of Toba 74,000 years ago.That eruption ejected 2,800 cubic kilometers of lava and ash and reduced average global temperatures by five to 15 degrees C. The consequences of such a chill were undoubtedly severe but did not last as long as once thought: sulfuric acid in the ice record disappeared after only six years; some researchers suggest that it vanished even earlier.”

//Volcanic ash vs sulfur aerosols//

"The primary role of volcanic sulfur aerosols in causing short-term changes in the world's climate following some eruptions, instead of volcanic ash, was hypothesized by scientists in the early 1980's. They based their hypothesis on the effects of several explosive eruptions in Indonesia and the world's largest historical effusive eruption in Iceland.

Scientists studied three historical explosive eruptions of different sizes in Indonesia--Tambora (1815), Krakatau (1883), and Agung (1963). They noted that decreases in surface temperatures after the eruptions were of similar magnitude (0.18-1.3 °C). The amount of material injected into the stratosphere, however, differed greatly. By comparing the estimated amount of ash vs. sulfur injected into the stratosphere by each eruption, it was suggested that the longer residence time of sulfate aerosols, not the ash particles which fall out within a few months of an eruption, was the paramount controlling factor (Rampino and Self, 1982).

In contrast to these explosive eruptions, one of the most severe volcano-related climate effects in historical times was associated with a largely nonexplosive eruption that produced very little ash--the 1783 eruption of Laki crater-row in Iceland. The eruption lasted 8-9 months and extruded about 12.3 km3 of basaltic lava over an area of 565 km2. A bluish haze of sulfur aerosols all over Iceland destroyed most summer crops in the country; the crop failure led to the loss of 75% of all livestock and the deaths of 24% of the population (H. Sigurdsson, 1982). The bluish haze drifted east across Europe during the 1783-1784 winter, which was unusually severe.

Clearly, these examples suggested that the explosivity of an eruption and the amount of ash injected into the stratosphere are not the main factors in causing a change in Earth's climate. Instead, scientists concluded that it must be the amount of sulfur in the erupting magma.

The eruption of El Chichon, Mexico, in 1982 conclusively demonstrated this idea was correct. The explosive eruption injected at least 8 Mt of sulfur aerosols into the atmosphere, and it was followed by a measureable cooling of parts of the Earth's surface and a warming of the upper atmosphere. A similar-sized eruption at Mount St. Helens in 1980, however, injected only about 1 Mt of sulfur aerosols into the stratosphere. The eruption of Mount St. Helens injected much less sulfur into the atmosphere--it did not result in a noticeable cooling of the Earth's surface. The newly launched TOMS satellite (in 1978) made it possible to measure these differences in the eruption clouds. Such direct measurements of the eruption clouds combined with surface temperatures make it possible to study the corrleation between volcanic sulfur aerosols (instead of ash) and temporary changes in the world's climate after some volcanic eruptions.

//Volcanic interactions with the atmosphere//

The most significant impacts from large explosive eruptions come from the conversion of sulfur dioxide (SO2) to sulfuric acid (H2SO4), which condenses rapidly in the stratosphere to form fine sulfate aerosols. The aerosols increase the reflection of radiation from the Sun back into space and thus cool the Earth's lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the stratosphere.

>>>> =====**Volcanic winter**=====

"Even if VEI 8 events could be accurately predicted, and local and regional precautions and evacuations were to take place, the regional and global effects of the ash fallout and aerosol clouds on climate, agriculture, health, and transportation would present a severe challenge to modern civilisation. The major effect on civilization would be through collapse of agriculture as a result of the loss of one or more growing seasons (Toon et al. 1997). This would be followed by famine, the spread of infectious diseases, breakdown of infrastructure, social and political unrest, and conflict. Volcanic winter pre- dictions are for global cooling of 3 to 5◦C for several years (Fig. 1) and regional cooling up to 15◦C (Rampino and Self 1992, Rampino and Ambrose 2000). This could devastate the major food-growing areas of the world. For example, the Asian rice crop could be destroyed by a single night of below-freezing temperatures during the growing season. In the temperate grain- growing areas, similar drastic effects could occur. In Canada, a 2 to 3◦C average local temperature drop in the growing season would destroy wheat production, and a 3 to 4◦C drop would halt all Canadian grain production. Crops in the American Mid- west and the Ukraine could be severely injured by a 3 to 4◦C temperature decrease (Harwell and Hutchinson 1985, Pittock et al. 1986). Severe climate would also interfere with global transportation of foodstuffs and other goods. Thus, a Toba-sized (VEI = 8) eruption would compromise global agriculture, lead- ing to famine and possible disease pandemics (Stothers 1999).

Furthermore, large volcanic eruptions might lead to longer term climatic change through positive feedback effects on climate such as cooling the surface oceans, formation of sea-ice, or increased land ice (Rampino and Self 1992, 1993), prolong- ing recovery from the “volcanic winter.” The result could be widespread starvation, famine, disease, social unrest, financial collapse, and severe damage to the underpinnings of civilization (Sagan and Turco 1990).

The location of a supereruption can also be an important fac- tor in its regional and global effects. Eruptions from the Yellow- stone Caldera over the last 2 million years include the 2500 km3 Huckleberry Ridge Tuff (2 Myr), the 280 km3 Mesa Falls Tuff (1.3 Myr), and the 1000 km3 Lava Creek Tuff (0.6 Myr). Each of these produced thick ash deposits over the western and cen- tral United States (compacted ash thicknesses of 0.2 m occur ∼1500 km from the source; Wood and Kienle 1990, Sarna- Wojcicki and Davis 1991). Thus, in addition to the global cli- matic consequences of these Yellowstone supereruptions, they would have directly devastated the major grain-producing areas in the breadbasket of North America, preventing agricultural recovery for years.

One mitigation strategy could involve the stockpiling of global food reserves. In considering the vagaries of normal climatic change, Schneider and Londer (1984) noted that when grain stocks dip below about 15% of utilization, local scarcities, world- wide price jumps, and sporadic famine were more likely to occur. They suggested that a minimum world level of accessible grain stocks near 15% of global utilization should be maintained as a hedge against year-to-year production fluctuations due to cli- matic and socioeconomic disruptions. This does not take into account social and economic factors that could severely limit rapid and complete distribution of food reserves.

At present, a global stockpile equivalent to a two-month global supply of grain exists (Smith 2000), which is about 15% of annual consumption. For a volcanic VEI 8 catastrophe, however, several years of growing season might be curtailed (Zielinski et al. 1996a, Rampino and Ambrose 2000), and hence a much larger stockpile of grain and other foodstuffs would have to be maintained, along with the means for rapid global distribution.

Burrows and Shapiro (1999) take a wider view. They propose that space exploration can be the vehicle for development of an interplanetary repository for terrestrial civilization. This would mean the transfer of human civilization, along with all tech- nological and cultural information, to other places in the Solar System for safekeeping. The repository would be a means of providing a backup system for the planet, fostering recovery of terrestrial civilization in the wake of global disasters such as as- teroid collisions or volcanic catastrophes. This might sound like science fiction, but such a strategy will soon be technologically feasible."

"Present human civilization, de- pendent largely on annual crop yields, is vulnerable to an “im- pact winter” that would result from dust lofted into the strato- sphere by the impact of objects ≥1 km in diameter (Chapman and Morrison 1994, Toon et al. 1997). The threshold for global catas- trophic climatic cooling and possible ozone layer destruction is estimated to be a 1–2-km-diameter asteroid or comet (Chapman and Morrison 1994). Such an impact would release about 105 to 106 Mt (TNT equivalent) of energy, produce a crater ∼20–40 km in diameter, and is calculated to generate a global cloud consist- ing of ∼1000 Mt of submicron dust (Toon et al. 1997). Covey et al. (1990) performed 3-D climate-model simulations for a global dust cloud containing submicron particles with a mass corresponding to that produced by an impact of 6 × 105 Mt (TNT). In this model, global temperatures dropped by ∼8◦C during the first few weeks. Chapman and Morrison (1994) estimated that an impact of this size would kill >1.5 billion people through direct and indirect effects."

"What about the threat from volcanic supereruptions? Chapman and Morrison (1994) suggested that the global cli- matic effects of VEI = 8 eruptions such as Toba might be simi- lar to those of the impact of an ∼1-km-diameter (106 Mt TNT) asteroid. Impact by an ∼1-km-diameter asteroid is estimated to put about 10^15 g of fine submicron dust into the stratosphere (Toon et al. 1997), which is comparable to the amount of strato- spheric dust and aerosols predicted for supereruptions (Rampino and Self 1992). Fine volcanic dust and sulfuric acid aerosols have optical properties similar to the submicron dust produced by impacts (Toon et al. 1997), and the effects on atmospheric opacity should be similar. Volcanic aerosols, however, have a longer residence time of several years (Bekki et al. 1996) compared to a few months for fine dust, so a huge eruption would be expected to have a longer lasting effect on global climate than an impact producing a comparable amount of atmospheric loading.

Estimates of the frequency of large volcanic eruptions of VEI 8 that could cause “volcanic winter” conditions suggest that they should occur about once every 50,000 years. This is approximately a factor of 2 more frequent than asteroid or comet collisions that might cause climate cooling of similar severity. Moreover, predicting or preventing a volcanic climatic disaster might be more difficult than tracking and diverting incoming as- teroids and comets. These considerations suggest that volcanic supereruptions pose a real threat to civilization, and efforts to predict and mitigate volcanic climatic disasters should be con- templated seriously."

"Dust and gases injected by an eruption into the stratosphere reflect solar radiation back to space and absorb heat themselves, cooling the lower atmosphere. This fact has led to the concept of ‘volcanic winter’. Silicate dust (made of tiny ash particles) is thought to be less important, because its residence time in the stratosphere is quite short (only a few weeks to months at most). The main factor causing global cooling after a major eruption is sulphur dioxide gas, which reacts with water to form tiny droplets of sulphuric acid, and these remain in the stratosphere for two or three years as an aerosol."

"...researchers have reported evidence of an unusually large volcanic eruption in Italy around 40,000 years ago that created a "volcanic winter" that devastated the ecology of southern and eastern Europe."

"Recently, observations from ice cores have been made on the possible effects of the Toba super-eruption, 74,000 years ago. If these data do reflect the Toba event, they suggest that aerosol formation and fallout lasted for six years. The volcanic winter would not only be more severe than for a Pinatubo-scale eruption, but would last much longer. Models suggest that a Toba-sized super-eruption would inject so much sulphur gas into the atmosphere that the stratosphere chemistry would be substantially perturbed – allowing for more prolonged climate-forcing. Some models suggest super eruptions can cause cooling of 3–5°C, which in global climate terms represents a catastrophic change.

It may not sound like much, but a mere 4°C cooling, sustained over a long period, is enough to cause a new Ice Age. However, great caution is needed in attributing causes and effects in a system as complex as global climate, and more detailed modelling research is required. Initial computer climate-model runs by scientists at the UK Meteorological Office’s Hadley Centre for a Toba-sized eruption suggest Northern Hemisphere temperature drops of 10°C. This would freeze and kill the equatorial rainforests."

//Comparisons with nuclear winter//

"Study of large volcanic eruptions’ climatic effects was boosted during the 1980s by the issue of the potential long-term environmental effects of thermonuclear war. From this research, the concept of “nuclear winter” – pronounced cooling in the few years following such a war – emerged. In a nuclear war, large amounts of dust and smoke would be injected into the atmosphere. Data from volcanic eruptions like Mount Pinatubo later provided opportunities to test “nuclear winter” models. It emerged that the main cause of disaster would be destruction of global agriculture and food supply. After a year of severely reduced food supply, there would be mass starvation. Because a nuclear winter might last two or three years, scientists concluded that this would threaten the continued existence of civilisation (and possibly even our species). Casualties from the immediate consequences of nuclear winter due to direct destruction and radioactive contamination would be few compared with those due to mass starvation. This apocalyptic depiction of the consequences of nuclear war by the scientific community had a profound influence in governmental efforts to reduce the world’s nuclear arsenals and the threat of conflict.

The possibility that super-eruptions might have the same effects as nuclear war, by causing severe volcanic winters, is one reason why our working group wishes to draw attention to this natural volcanic phenomenon."

"Since Toba is a low-latitude volcano, dust and volatiles would have been injected efficiently into both Northern and Southern Hemispheres (Rampino et al., 1988), although the season of the eruption is unknown. These estimated aerosol optical effects are roughly equivalent in visible opacity to smoke-clouds (Turco et al., 1990), which is within the range used in nuclear winter scenarios of massive emissions of soot emanating from burning urban and industrial areas in the aftermath of nuclear war.

Although the climate conditions and duration of a nuclear winter have been much debated, simulations by Turco and others (1990) predicted that land temperatures in the 3O°- 7O°N latitude zone could range from approximately 5°C to approximately 15°C colder than normal, with freezing events in mid-latitudes during the first few months. At lower latitudes, model simulations suggest cooling of 10° С or more, with drastic decreases in precipitation in the first few months. Ocean-surface cooling of approximately 2-6° С might extend for several years, and persistence of significant soot for 1-3 years might lead to longer term (decadal) climatic cooling, primarily through climate feedbacks including increased snow cover and sea ice, changes in land surface albedo, and perturbed sea-surface temperatures (Rampino and Ambrose, 2000).

The injection of massive amounts of volcanic dust into the stratosphere by a supereruption such as Toba might be expected to lead to similar immediate surface cooling, creating a 'volcanic winter' (Rampino and Self, 1992; Rampino et al., 1988). Volcanic dust probably has a relatively shorter residence time in the atmosphere (3-6 months) than soot (Turco et al., 1990) and spreads from a point source, but volcanic dust is injected much higher into the stratosphere, and hence Toba ash could have had a wide global coverage despite its short lifetime. Evidence of the wide dispersal of the dust and ash from Toba can be seen from lake deposits in India, where the reworked Toba ash forms a layer up to 3 m thick, and from the widespread ash layer in the Indian Ocean and South China Sea (Acharya and Basu, 1993; Huang et al., 2001; Shane et al., 1995).

Evidence for rapid and severe cooling from the direct effects of volcanic ash clouds comes from the aftermath of the 1815 Tambora eruption. Madras, India experienced a dramatic cooling during the last week of April 1815, a time when the relatively fresh ash and aerosol cloud from Tambora (10-11 April) would have been overhead. Morning temperatures dropped from 11°C on Monday to -3°C on Friday (Stothers, 1984a). A similar, but much smaller effect, occurred as the dust cloud from the 1980 Mt St Helens eruption passed over downwind areas (Robock and Mass, 1982).

The stratospheric injection of sulphur volatiles (>1015g), and the time required for the formation and spread of volcanic H2SO4 aerosols in the stratosphere should lead to an extended period of increased atmospheric opacity and surface cooling. The ice-core record, however, indicates stratospheric loadings of 1014 to 1015 g of H2SO4 aerosols for up to 6 years after the eruption (Zielinski et al., 1996a).

This agrees with model calculations by Pope and others (1994) that predict oxidation lifetimes (time required to convert a given mass of sulphur into Super-volcanism and other geophysical processes H2SO4 aerosols) of between 4 and 17 years, and diffusion lifetimes (time required to remove unoxidized SO2 by diffusion to the troposphere) of between 4 and 7 years for total sulphur masses between 1015 and 1016 g. For atmospheric injection in this range, the diffusion lifetime is the effective lifetime of the cloud because the SO2 reservoir is depleted before oxidation is completed.

If the relationship between Northern Hemisphere cooling and aerosol loading from large eruptions is approximately linear, then scaling up from the 1815 AD. Tambora eruption would lead to an approximately 3.5°C hemispheric cooling after Toba (Rampino and Self, 1993a). Similarly, empirical relationships between SO2 released and climate response (Palais and Sigurdsson, 1989) suggested a hemispheric surface-temperature decrease of about 4 ± 1°C. The eruption clouds of individual historic eruptions have been too short-lived to drive lower tropospheric temperatures to their steady-state values (Pollack et al., 1993), but the apparently long-lasting Toba aerosols may mean that the temperature changes in the troposphere attained a larger fraction of their steady-state values. Huang et al. (2001) were able to correlate the Toba ash in the South China Sea with a 1°C cooling of surface waters that lasted about 1000 years.

Considering a somewhat smaller super-eruption, the Campanian eruption of approximately 37,000 cal yr BP in Italy (150 km3 of magma discharged) was coincident with Late Pleistocene bio-cultural changes that occurred within and outside the Mediterranean region. These included the Middle to Upper Paleolithic cultural transition and the replacement of Neanderthals by 'modern' Homo sapiens (Fedele et al., 2002)."

>>>> =====**Ozone depletion**=====

//Ozone depletion promoted by volcanic sulfur aerosols//

The sulfate aerosols also promote complex chemical reactions on their surfaces that alter chlorine and nitrogen chemical species in the stratosphere. This effect, together with increased stratospheric chlorine levels from chlorofluorocarbon (CFC) pollution, generates chlorine monoxide (ClO), which destroys ozone (O3)."

"Chlorine gases emitted can damage the ozone layer. On top of the damage we have already inflicted via CFCs, the eruption of a supervolcano could deplete the ozone layer to such an extent that it becomes another deadly side-effect. The increase in ultra-violet radiation would cause skin cancer in humans and damage crops."

"The presence of volcanic aerosols can accelerate ozone-destroying reactions and affect changes in nitrogen in the stratosphere as well as tropospheric carbon monoxide concentrations. Ozone is destroyed by anthropogenically-released chemicals, and it appears that volcanic aerosols can act to catalyse these reactions. While the ozone layer remains vulnerable, a super-eruption could further adversely affect the deterioration of the ozone layer, which is essential for life on Earth because it shields us from severe ultraviolet radiation."

"Ozone depletion – stratospheric aerosols will serve to catalyse ozone loss, permitting more UV-B flux to the ground in high–mid latitude regions, the effect lasting a few years after the eruption."

>>>>> ======**UV Radiation**======


 * Health effects of UV radiation**

"Small amounts of UV are beneficial for people and essential in the production of vitamin D. UV radiation is also used to treat several diseases, including rickets, psoriasis, eczema and jaundice. This takes place under medical supervision and the benefits of treatment versus the risks of UV radiation exposure are a matter of clinical judgement.

Prolonged human exposure to solar UV radiation may result in acute and chronic health effects on the skin, eye and immune system. Sunburn (erythema) is the best-known acute effect of excessive UV radiation exposure. Over the longer term, UV radiation induces degenerative changes in cells of the skin, fibrous tissue and blood vessels leading to premature skin aging, photodermatoses and actinic keratoses. Another long-term effect is an inflammatory reaction of the eye. In the most serious cases, skin cancer and cataracts can occur.

Between 2 and 3 million non-melanoma skin cancers, e.g. basal cell carcinomas and squamous cell carcinomas, are diagnosed each year, but are rarely fatal and can be surgically removed. Approximately 130,000 malignant melanomas occur globally each year, substantially contributing to mortality rates in fair-skinned populations. An estimated 66,000 deaths occur annually from melanoma and other skin cancers.

Worldwide some 12 to 15 million people become blind from cataracts annually, of which up to 20% may be caused or enhanced by sun exposure according to WHO estimates. Furthermore, a growing body of evidence suggests that environmental levels of UV radiation may suppress cell-mediated immunity and thereby enhance the risk of infectious diseases and limit the efficacy of vaccinations. Both of these act against the health of poor and vulnerable groups, especially children of the developing world. Many developing countries are located close to the equator and hence, people are exposed to the very high levels of UV radiation that occur in these regions.

It is a popular misconception that only fairskinned people need to be concerned about overexposure to the sun. Darker skin has more protective melanin pigment, and the incidence of skin cancer is lower in darkskinned people. Nevertheless, skin cancers do occur with this group and unfortunately they are often detected at a later, more dangerous stage. The risk of UV radiation-related health effects on the eye and immune system is independent of skin type.

For further reading beyond the following web sites a comprehensive summary and review of UV-related health effects can be found in the WHO Environmental Health Criteria Monograph Ultraviolet Radiation Global burden of disease assessment

WHO has now published the report entitled "Global burden of disease from solar ultraviolet radiation" that provides detailed estimates of UV-associated disease burden worldwide. Using established methodology and best available estimates on UV-related mortality and morbidity, this report estimates that annually around 1.5 mill DALYs (Disability-adjusted life years) are lost through excessive UV exposure. The report gives region, age and sex-specific estimates and includes detailed methodological considerations. A counterfactual zero population exposure to UV would generate a substantial burden of disease through diseases of vitamin D deficiency. This, however, is only a theoretical possibility since the large majority of people is casually exposed to UV radiation such that extremely low Vitamin D levels are rarely found."

"Stratospheric aerosols are usually too sparse to have any effect on atmospheric UV transmission. An exception arises following a major volcanic eruption, such as that of Mt. Pinatubo (Philippines) in June 1991 which injected large amounts of ash and sulfur dioxide (SO2) into the stratosphere. The heavier ash sedimented out of the stratosphere relatively quickly and its optical effects were of limited geographical extent. Gaseous SO2, on the other hand, was removed from the stratosphere mainly by chemical reactions to form H2SO4 molecules, which then readily nucleated into sulfate aerosol particles. Higher stratospheric sulfate aerosol loadings were observed for several years after the eruption, during which time these particles were distributed on global scales. Calculations indicate that the effects on biologically weighted UV irradiances were quite small, of order of a few percent (Madronich et al., 1991; Vogelmann et al., 1992; Tsitas and Yung, 1996), with even some possible enhancements at very short wavelengths and low sun when aerosols scatter some photons directly downward thus allowing a shorter crossing of the stratospheric ozone layer (Michelangeli et al., 1992; Davies, 1993). Ground-based measurements of UV irradiance after the Mt. Pinatubo eruption confirm the small decreases and also show a strong increase in diffuse/direct radiation at all wavelengths, in good agreement with theoretical models (Blumthaler and Ambach, 1994; Zeng et al., 1994, Lantz et al., 1996). A less direct but more important UV-related consequence of stratospheric aerosols is their effect on stratospheric ozone itself. Significant destruction of stratospheric ozone by heterogeneous chemical processes involving the aerosols was predicted (Hoffman and Solomon, 1989; Brasseur et al., 1990) and observed for several years after the Mt. Pinatubo eruption (Gleason et al., 1993; WMO, 1994a)."

[|Vital Ozone Graphics]

[| ENVIRONMENTAL HEALTH CRITERIA 160: ULTRAVIOLET RADIATION]

Allen, J., 2001, [|Ultraviolet Radiation: How It Affects Life on Earth], Earth Observatory

>> ===Social Collapse===

"Disruption of national and international relief efforts and cooperation. Disruption of some communications (satellites may not be able to recieve or transmit information normally due to ash and/or aerosols in the lower atmosphere. Possible effects of all the above on world financial markets."

>> ===Psychological Effects===

=Historic sources=

"26,500 years ago - Lake Taupo, NZ - 1,170 km³ 74,000 years ago - Lake Toba, Sumatra - 2,800 km³ 254,000 years ago - Whakamaru, NZ - 1,200-2,000 km³ 640,000 years ago - Yellowstone, USA - 1,000 km³ 2.1 million years ago - Yellowstone, USA - 2,500 km³ 2.5 million years ago - Cerro Galan, Argentina - 1,050 km³ 4 million years ago - Atana Ignimbrite, Chile - 2,500 km³ 4.5 million years ago - Yellowstone, USA - 1,800 km³ 6.6 million years ago - Yellowstone, USA - 1,500 km³ 27.8 million years ago - La Garita Caldera, USA - 5,000 km³ 29.5 million years ago - Sam Ignimbrite, Yemen - 5,550 km³"



> ==Yellowstone==

[|Truth, fiction and everything in between at Yellowstone] Jake Lowenstern, scientist-in-charge of the Yellowstone Volcano Observatory, about the rumours of a pending Yellowstone eruption.

[|The initial dispersal and radiative forcing of a Northern Hemisphere mid-latitude super volcano: a model study] C. Timmreck, H.-F. Graf

[|Supervolcano] (docudrama) A two-part BBC factual drama asked: What if Yellowstone erupted?

> ==Toba==



[|The super-eruption of Toba, did it cause a human bottleneck?] F.J. Gathorne-Hardy, W.E.H. Harcourt-Smith

[|Did the super-eruption of Toba cause a human population bottleneck? Reply to Gathorne-Hardy and Harcourt-Smith], Stanley H. Ambrose

[|‘The TOBA Super-eruption’ project]

[|Volcanic Winter and Accelerated Glaciation following the Toba Super-eruption], Michael R. Rampino, Stephen Self

[|Dispersal of Ash in the Great Toba Eruption, 75 ka], W. I. Rose, C. A. Chesner

[|Climate–Volcanism Feedback and the Toba Eruption of ~74,000 Years ago], Michael R. Rampino, Stephen Self

[|Potential Atmospheric Impact of the Toba Mega‐Eruption ~71,000 years ago], Zielinski, G. A.; Mayewski, P. A.; Meeker, L.D.; Whitlow, S.; Twickler, M.S.; Taylor, K.

> ==Phlegrean Fields==

[|Vesuvius's big daddy: The supervolcano that threatens all life in Europe]

> ==Altiplano-Puna==

[|Altiplano-Puna volcanic complex of the central Andes] S. L. de Silva

> ==Permian Extinction==

[|Ancient mass extinction tied to torched coal]

[|Catastrophic dispersion of coal fly ash into oceans during the latest Permian extinction]

[|Researchers find smoking gun of world's biggest extinction]

=Other Sources=

[|ScienceNOW - Up to the minute news from ScienceGiving Earth an Umbrella]

[|The International Volcanic Health Hazard Network (IVHHN)]

[|THE HEALTH HAZARDS OF VOLCANIC ASH - A guide for the public], IVHHN [|GUIDELINES ON PREPAREDNESS BEFORE, DURING AND AFTER AN ASHFALL] IVHHN

[|super volcanism and other geophysical processes of catastrophic import] - [|Rampino, Michael R.]

[|The size and frequency of the largest explosive eruptions on Earth]

[|On the Truly Noncooperative Game of Life on Earth: In Search of the Unity of Nature & Evolutionary Stable Strategy]

[|Volcanic winters]