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October 2007 Issue
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A close thing for mankind?


While mapping river deposits in north-central India in 1980, University of Adelaide geomorphologist Professor Martin Williams made a surprise discovery of volcanic ash.

Volcanic ash younger than a few million years was unheard of in India, and Professor Williams eventually traced it to the eruption, about 73,000 years ago, of Toba in northern Sumatra.

Toba ejected at least 1000 cubic kilometres of ash and rock fragments, making Krakatoa, which spewed out a mere 14-18 cubic km, look mild in comparison. The eruption of Krakatoa, however, killed 42,000 people and global temperatures dropped nearly one degree over the next few years.

The discovery in India and consequent findings by researchers around the globe have led to the theory that Toba's eruption came close to killing off the world's human population. There was a sharp decline in human genetic diversity between 100,000 and 50,000 years ago - the result, geneticists believe, of a world population which suddenly plummeted from hundreds of thousands to a few thousand.

Professor Williams said "the jury is still out" on whether Toba caused this level of human catastrophe but his recent research has added significant weight to the argument.

Analysis of pollen preserved in marine cores in the Bay of Bengal and off Sumatra indicates dramatic regional cooling followed by many centuries of drought. Analysis also of fossil soils above and beneath the Toba ash in a transect across central India points to a dramatic change from forests to grasslands and patchy woodlands after Toba.

"Impacts on ecosystems of this magnitude could well have significantly affected animal and human societies," Professor Williams said.

The Toba story continues but it is just one aspect of the wide-ranging research Professor Williams conducts on reconstructing environment and climatic changes over the past two million years, the Quaternary period.

"Operating at different time scales and working in different areas of northern Africa and the drier parts of India, China, Australia and the Middle East, I've been trying to reconstruct patterns of past environmental changes using as many different lines of evidence as possible," Professor Williams said.

He has worked with international teams from around the world on a variety of different projects with research outcomes now part of everyday conventional wisdom - such as the pioneering work on El Niņo effects that dictate major floods and synchronous droughts in many different locations from the Nile basin to parts of China, South America, Indonesia, India and eastern Australia.

In recognition of his distinguished and sustained contributions to Quaternary research, Professor Williams was recently elected an Honorary Member by the International Union of Quaternary Research, only the second Australian to receive this honour.

Professor Williams came to the University of Adelaide in 1993 as Director of the Mawson Graduate Centre for Environmental Studies and Foundation Professor of Environmental Studies.

He is author of more than 250 scientific papers and has authored or edited 11 books, including the significant text Quaternary Environments that has seen two editions and a Chinese edition.

He is a member of the Scientific and Technical Advisory Panel of the Global Environment Facility and has been frequent adviser to the World Bank, the Asia Development Bank and the UN International Development Programme on the control of desertification and land degradation in Africa, Central Asia and China.

Professor Williams has also been awarded the Royal Society of South Australia's top honour, the Verco Medal. (See Royal Society honours for two).

Story by Robyn Mills

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Professor Martin Williams at the edge of an impact crater in the Mauritanian Desert, Western Sahara
Photo by Dr Helene Jousse

Professor Martin Williams at the edge of an impact crater in the Mauritanian Desert, Western Sahara
Photo by Dr Helene Jousse

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