Wednesday, June 6, 2007

The Toba Winter

The eruption of the Toba Volcano, 74,000 years ago, was the largest in the last 2 million years. This "supervolcanic eruption" ejected 2800 cubic km of ash into the atmosphere; by comparison, the 1980 eruption of Mt. St. Helens produced 1 cubic km of ash. Twenty foot layers of compacted Toba ash has been found in central India, 1900 miles from the volcano. Today, the remnant caldera of this violent explosion, located in northern Sumatra, is up to 60 miles in diameter; Lake Toba fills much of this basin and a new volcanic dome forms a large island near its western shore.

Climatologists believe that the Toba eruption produced a "volcanic winter" that lasted for several years, lowering worldwide temperatures by 5 degrees C or more. Furthermore, DNA studies indicate a significant reduction of the human population, perhaps to 10,000 individuals or less, that seems to coincide with this event. At the time of the Toba eruption, early man had spread out of Africa and was colonizing the southern rim of Asia. Ashfall from the volcano was most intense throughout this region and few humans likely survived. It is theorized that a small, residual population in southeast Africa kept the human species from becoming extinct.

Though better prepared with our modern technologies, we remain vulnerable to such a devastating, natural catastrophe. The Yellowstone Caldera, in northwest Wyoming, is the remnant of three eruptions over the past 2 million years; the first and largest of these was a supervolcanic eruption, only 10% smaller than the Toba event. The floor of the caldera has been gradually rising in recent decades and some volcanologists believe that another major eruption is just a matter of time.