Toba, supervolcano in Indonesia
Lake Toba is in the middle of Northern Sumatra. It lies about two hundred miles from the epicenter of the magnitude 9.3 earthquake that devastated Asia in late December 2004, as its tsunami swept across the Indian Ocean. This lake is known as a caldera, the technical term for the crater formed by a volcanic eruption. It is a big lake, eighteen by sixty miles in extent and as deep as five thousand feet in places. The size of the lake can be attributed to Toba’s eruption, which was the largest that has occurred, anywhere on earth, within the past two million years. About 74,000 years ago a high volcanic mountain that stood on the area, now occupied by Lake Toba, erupted and blew skyward a mass of ash and volcanic debris that was three thousand times as big as the total amount that erupted from Mount St. Helens in 1980. The entire subcontinent of India was covered with ash. All around the globe sunshine was reduced and temperatures dropped by about 3 degrees, and stayed at that level for years. During that time, throughout the world, millions of all forms of life died. Thousands of species vanished.
Today humanity is warned that increasing emission of carbon dioxide in the atmosphere will destroy human life and our cities before the end of this century unless we change our ways and reduce the present levels of carbon dioxide. Yet, beneath our feet are forces of change far more destructive for the earth’s environment and all of its occupants than anything that human activity has done or can ever do. Toba was one of the biggest of all within the last two million years with a Volcanic Explosivity Index (VEI) of 8. It is now the model by which geologists assess worst-case scenarios for the future.
There are only about half a dozen locations around the world where geologists have identified super volcanoes. One location is in New Zealand, one in Japan, and one in Russia. In the United States there is one in Yellowstone National Park where there was an eruption of strength 8 on the VEI, about 640,000 years ago. That strength represents a tenth of Toba’s and a hundred times the strength of Krakatau. Although it’s VEI would only be one-tenth that of Toba, it would be disastrous. Tambora, an Indonesian volcanic eruption of 1815, was ten times stronger than Krakatau and only a tenth as strong as the ancient Yellowstone one yet it caused widespread destruction of life and agriculture all over the world.
Now it is clear that the dust cloud from the explosion, one that reached high into the atmosphere because it happened near the equator, reduced the amount of sunshine that could reach the earth. Ad the eruption occurred near the North Pole the atmospheric dust would have stayed at a lower level within the atmosphere.
Geneticists believe that Toba had a particularly catastrophic effect on humans who, 74,000 years ago, were still at an early stage of development. The population on Earth may have been reduced to a few thousand people, pushing humanity to the edge of extinction. The evidence for the catastrophic reduction of numbers around the time of Toba comes from an analysis of mitochondrial DNA that revealed a limited genetic diversity, far lower than the known age of humans would indicate. The total numbers of humans in the years following Toba seemed to be no more than ten thousand. Not until 50,000 years ago, 20,000 years after Toba, was there evidence of a rapid and widespread increase in the numbers of humans. In order to test the validity of their calculations regarding humans, geneticists examined the mitochondrial DNA of chimpanzees to find out if they too had been victims of the same environmental disaster. The results were conclusive. They had experienced a bottleneck similar to human DNA.
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