Super Volcanoes

A supervolcano is an arbitrary definition for volcanoes that can have the largest of eruptions. It is such a recent term, the spelling of the word is not yet set in concrete, but we'll use the spelling most commonly used.

While there is no precise measurement used to qualify a volcano as "super", the word is used to describe a volcano that can threaten global civilization. A supervolcano will either wipe out all of humankind, or make a very good attempt to do so. It is the only local, natural event that has such power, and ranks alongside comets and asteroids as a force of nature we should fear. 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.

They are rare enough to be missing from modern history, and we only know they have ever occurred due to geological studies of the clues they have left for us.

How Bad Can a Supervolcano Be? The supereruption of Toba caused temperatures to drop globally by between 3 and 9 degrees Fahrenheit, 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) Tephra is the fragmental material created by a volcanic eruption. Different types of tephra are determined by size - anything larger than 2.5 centimeters is called a "bomb", and ash is the smallest. Volcanic ash is quite different to the ash you get from burning 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. 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. 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 deafening, and was heard 3,000 miles away. Research into some likely large eruptions from 6th century (El Chichon) and 13th century (Proto Krakatoa) suggest that they may have also caused famines, in each case leading to a widespread plague outbreak, and possibly, in the case of the former, causing the Dark Ages. 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.

Examples of Super Volcanoes

1.The Yellowstone Caldera

Unbeknownst to most, Yellowstone National Park sits on a subterranean chamber of molten rock and gasses so vast that it is arguably one of the largest active volcanoes in the world. A magma chamber not far below the surface fuels all the volcanic attractions that Yellowstone is famous for. The last major eruption at Yellowstone, some 640,000 years ago, ejected 8,000 times the ash and lava of Mount St. Helens. It is alive and well today, and is the scientific basis for the hilarious volcanic explosion seen in the movie 2012 that blew up Woody Harrelson and, somehow, NOT John Cusack.

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2.The Long Valley Caldera

Second only to Yellowstone in North America is the Long Valley caldera, in east-central California. The 200-square-mile caldera is just south of Mono Lake, near the Nevada state line. The biggest eruption from Long Valley was 760,000 years ago, which unleashed 2,000 to 3,000 times as much lava and ash as Mount St. Helens, after which the caldera floor dropped about a MILE, according to the U.S. Geological Survey. Some of the ash reached as far east as Nebraska. What worries geologists today was a swarm of strong earthquakes in 1980 and the 10-inch rise of about 100 square miles of caldera floor. Then, in the early 1990s, large amounts of carbon dioxide gas from magma below began seeping up through the ground and killing trees in the Mammoth Mountain part of the caldera. When these sorts of signs are present, it could mean trouble is centuries, decades, or even YEARS away, say volcanologists.

3.Valles Caldera

The 175-square-mile Valles caldera forms a large pock in the middle of northern New Mexico, west of Santa Fe. It last exploded 1.2 million and 1.6 million years ago, piling up 150 cubic miles of rock and blasting ash as far away as Iowa. As with other calderas, there are still signs of heat below: hot springs are still active around Valles. Geologists suspect the cause of Valles caldera has something to do with how the western United States' portion of the North American tectonic plate is being pulled apart.

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4.Lake Toba

The 1,080-square-mile Toba caldera in North Sumatra, Indonesia is the only supervolcano in existence that can be described as Yellowstone's "big" sister. About 74,000 years ago, Toba erupted and ejected several thousand times more material than erupted from Mount St. Helens in 1980. Some researchers think that Toba's ancient super eruption and the global cold spell it triggered might explain a mystery in the human genome. Our genes suggest we all come from a few thousand people just tens of thousands of years ago, instead of from a much older, bigger lineage — as the fossil evidence testifies. Both could be true if only a few small groups of humans survived the cold years following the Toba eruption.