18 April 2005

Just when you thought it was safe to go back to Yellowstone

Anyone watching Supervolcano tonight probably went happily to sleep thinking to themselves that Yellowstone is a long way from Australia. Welcome to Lake Toba

According to the Toba catastrophe theory, modern human evolution was affected by a recent large volcanic event. It was proposed by Stanley H. Ambrose[1] (http://www.anthro.uiuc.edu/faculty/ambrose/), of the University of Illinois at Urbana-Champaign. Knowledge of human prehistory is largely theoretical, but based in fossil, archaeological, and genetic evidence.

Within the last three to five million years, after human and ape lineages diverged from the hominid stem-line, the human line produced a variety of human species. According to the Toba catastrophe theory, a massive volcanic eruption changed the course of human history by severely reducing the human population (called a 'bottleneck'). Around 75,000 years ago the Toba caldera in Indonesia erupted with a force three thousand times more powerful than Mount St. Helens.

According to Ambrose, this led to a decrease in the average global temperatures by as much as 15°C. This massive environmental change is believed to have created population bottlenecks in the various human species that existed at the time; this in turn accelerated differentiation of the isolated human populations, eventually leading to the end of all the other human species except for the branch that became modern humans (see volcanic winter).

Some geological evidence and computed models support the plausibility of the Toba catastrophe theory, and genetic evidence suggests that all humans alive today, despite their apparent variety, are descended from a very small population (see mitochondrial Eve). Using the average rates of genetic mutation, some geneticists have estimated that this population lived at a time coinciding with the Toba event.

And just to ensure we all sleep sleep soundly at night...

Sleeping giants present the biggest threat of all
Ray Cas, from Monash University's School of Geosciences, said Lake Toba's next blast could be big enough to disrupt the world's climate and send a tsunami surging towards Australia.

Professor Cas said none of the world's 100 or so active super volcanoes had erupted in modern times. However, if one did, it would be 100 to 1000 times more powerful than Krakatoa's 1883 eruption.

He feared the threat was being overlooked, just as the danger posed by Indian Ocean tsunami had been ignored.

"The Boxing Day tsunami was going to happen sooner or later, but there were no warning systems. A super volcano will happen sooner or later, and there are limited warning systems," he said. "We certainly need to be improving our monitoring of super volcanoes. If any of these were to erupt we would see disaster on a magnitude greater than we have ever experienced."

When Lake Toba erupted 73,000 years ago the world's climate was balanced on the edge of an ice age, Professor Cas said.

"The eruption released 1000 cubic kilometres of ash and rock debris into the atmosphere, much of it as fine ash which blocked out solar radiation, kicking the world back into an ice age."

In addition to cooling the world, with devastating results for global agriculture, Lake Toba's next eruption would probably send a pyroclastic flow - a rush of superheated gas and ash - crashing into the sea with enough force to trigger a tsunami.

The volcano was definitely still active, influenced by the same movement of tectonics plates that triggered the December 26 and March 28 earthquakes.

Another super volcano overdue for eruption was Taupo, on New Zealand's North Island. "It has a big eruption every 2000 years and it last erupted about 2000 years ago".

The Lake Toba super eruption measured 8 on the Volcanic Explosivity Scale. Tambora in 1815 measured 7 and Krakatoa in in 1883 was a 6. The 1980 Mt St Helens eruption was a 5.

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