last updated 23rd January 06
By Shabna Eliza John, Hi-Tech Editorial Division

Super volcanoes and slumbering giants

Approximately 75,000 years ago, the volcano Toba, in Indonesia erupted producing close to 2800 cubic kilometers of ash, and reducing the world's population to a mere 10,000. Yellowstone in Wyoming, after being dormant for 600 thousand years, might blow up at any moment. Its after-effect should exceed Toba's in human death toll, and because of severe temperature declines, it is entirely possible that the Earth enters the next Ice Age lasting centuries.

The major volcanic eruptions of the past that caused climatic anomalies with long lasting effects were Tambora (1815), Krakatoa (1883) and Pinatubo (1991.)

In 1815, Tambora, a relatively normal volcano, erupted in Indonesia resulting in extreme weather. In the resulting bizzare series of warming and cooling cycles, Norwegian fisheries froze over, Eskimos relocated southwards in Scotland, and Chinese orange orchards blighted due to the cold.

Pinatubo's 1991 explosion in the Philippines scored six on the index and was one of the largest eruptions of this century. With Stromboli in southern Italy, Kilauea in Hawaii, Mount Pinatubo in Philippines, all vying for the title of "deadliest super volcano", it is entirely possible that America's imminent danger, Yellowstone could put all of them to shame as well as obliterate more than nine-tenths of Earth's inhabitants. Mt. St. Helens' 1980 eruption was a mere sneeze compared to what lies beneath America's Yellowstone. Yellowstone has been calculated to have a regular eruption cycle of 600,000 years. Having last erupted 640,000 years ago, Yellowstone may detonate any time.

AKIN TO ASTERIOD COLLISION
With effects akin to a run in with a 1km diameter asteroid, Earth is ten times more likely to experience a super volcano eruption than a collision with an asteroid.

With many volcanoes on Earth which can erupt with colossal consequences, the US Geological Survey (USGS) scientists are considering the social as well environmental consequences of large magnitude volcanic emissions. Such eruptions could change Earth's climate triggering a global freeze due to a "radiative balance" or "radiative forcing."

When a volcano erupts, it sends into the atmosphere CFCs that absorb terrestrial radiation as well as reduce the Sun's heat from reaching the Earth's surface. Resultant low troposphere temperatures and altered atmospheric circulation patterns can send Earth into perpetual winter. This distinct and atypical warming and cooling of different habitats can result in the dying out of many animals and plant species. More terrifying, the effects of these eruptions can linger up to three to four years in the atmosphere with severe environmental effects threatening global civilization.

What was most dangerous about Pinatubo was the aerosol disturbance of a 20 million ton sulphur dioxide cloud injected into the stratosphere up to an altitude of more than 20 miles. This sulphate aerosol reflected the Sun's radiation back into space. Earth cooled by as much as 1.3 degrees in the following three years. They also reacted with stratospheric chlorine levels resultant of man-made chlorofluorocarbon (CFC) pollution, thinning the ozone layer dramatically.

A MAJOR ROLE
The impending dangers of global warming have been discussed intensely for long. But in truth, Earth is 2-3 degrees cooler than 6,000 years ago. Increasing icebergs and a thicker Antarctic Ice Sheet are proof of this long-term trend of cooler temperatures. Volcanic eruptions play a major role in warmer oceans and cooler land.

Studying the significant variations in emissions of different volcanoes, USGS scientists have also compared these to man made emissions and the combined effect of these on our planet's environment. The most abundant component of volcanic gas is water vapour; closely followed by carbon dioxide and sulphur dioxide. Other emissions include hydrogen fluoride, hydrogen sulphide, and hydrogen chloride.

A greenhouse gas, carbon dioxide causes global warming, while sulphur dioxide causes global cooling. Of all these volcanic gas emissions, the more significant impact is from the conversion of sulphur dioxide to sulphuric acid (H2SO4), which condenses rapidly in the stratosphere to form fine sulphate aerosols.

Another reaction of sulphate aerosols is the altered levels of chlorine and nitrogen in the stratosphere. This, combined with existing chlorofluorocarbon pollution, generates chlorine monoxide (ClO), which destroys ozone (O3). Subsisting in the upper troposphere, these aerosols attract cirrus clouds which further modify the Earth's radiation balance.

Volcanic emissions also effect vegetation. The flora produced fewer sugars, but the soil released less carbon. With neither the microbial life in the soil nor the plants giving off CO2, new foliage growth decelerated. Following Pinatubo's explosion, the land mass in the hemisphere became a "carbon sink" taking in more carbon than was given out.

Other side-effects include ozone destruction and vog- water vapour, ash particles and other acid fumes in volcano gases combine to form acid rain and what is commonly called volcanic smog. Volcanic ash consisting of powdered rock and pumice can severely damage vegetation as well as every kind of habitation.

Studying various volcanoes, USGS scientists have better understood the dynamics of earth's evolution. The long-term consequences of a super eruption on the climate, the environment, and people are yet to be comprehended. Not even science fiction has come up with a plausible strategy to avert this Apocalypse.