Prehistoric ash clouds

The volcano that erupted in Iceland about a fortnight ago brought Europe to a standstill for days together.

The volcano that erupted in Iceland about a fortnight ago brought Europe to a standstill for days together. But not many know that the intensity of the eruption that caused such chaos in air traffic was just a small fraction of the kind of eruptions the earth witnessed a few hundred thousand years ago. A team of researchers led by Sheila Mishra and Sushama Deo from Punes Deccan College has been working at two sitesMorgaon,60 km from Pune,and Bori,about 100 km from Punethat reveal volcanic ash sediments belonging to the Toba volcano in Sumatra,about 3,000 km from India.

The sediments,which are a million years old,are revealed in one-to-two-km patches in these regions. While the maximum thickness of the layer in Morgaon is 0.5 metres,in Bori it measures about 2 metres. The ash was first discovered by a team of researchers from the University of Pune in 1989 at Bori and in 1991 at Morgaon, said Mishra,who along with Deo has been researching the geomorphology of these two sites and the tools found there.

The Toba volcano in Sumatra,which is known to have erupted frequently during prehistoric times,had at least four major eruptions. The first one was about 1.2 million years ago,followed by one that occurred 800,000 years ago,another 530,000 years ago and the most recent 75,000 years ago. Research shows that the erupted volcanic ash,of 60-120 microns,remains in the stratosphere for years and comes down with the rains, said Mishra,adding that the ash at Morgaon and Bori is believed to be 800,000 years oldpaleo magnetic dating is used to determine the age. We have also discovered skeletons of animals and other evidence that points to the fact that early man in these regions saw hard times, she said.

Is such a volcanic eruption likely to occur in the near future? Well,one cant rule it out but it will be a few hundred thousand years from now, Mishra says.

The project undertaken by the team in 2000 involves a study of tools that have been discovered at both these sites. While over 600 toolssharp and pointedhave been excavated in a 2-km stretch at Morgaon,Bori threw up about 120. The tools at Morgaon are older than the volcanic ash and those at Bori are younger, said Deo.

With a strong resemblance to the tools of the Acheulian culture that existed in Africa about 1.6 million years ago,the researchers are also speculating the migration of homo-erectus between Africa and India. Owing to the fact that the number of tools found at Morgaon and Bori is very small compared to those excavated in Africa,it is highly possible that the technique originated in Africa and was brought to India by migrants. When the migration took place is a question we hope to answer with this excavation, said Deo.