Visakhapatnam: Geologists believe that ash from a volcano was blown all the way from northern Sumatra, Indonesia, for 2,500 km some 74,000 years ago and was deposited at two sites at the famous hill station Araku Valley in Vizag district.

Until now, the presence of ash from the volcano Toba was documented by geologists only at the Sagileru valley belt in Kurnool district in Andhra Pradesh, the Kukadi river valley at Bori, Maharashtra, Mahanadi and Brahmani river basins and Vamsadhara and Nagavali river basins in Odisha.

The supereruption of the Toba volcano is recognised as one of earth’s largest known eruptions and was certainly the largest of the Quaternary period. It is hypothesised by geologists and archeologists that the eruption led to both global climatic deterioration and the decimation of modern human populations.

Both the deposits in Araku that carry both archeological and historic value and evidence are in a dire state, unattended and in shambles. Shrubs are seen on top of the two ash deposits with goats grazing around.

Prof. D. Rajasekhar Reddy, national geo-heritage sites cell adviser for the Indian National Trust for Art and Cultural Heritage and a former professor of Andhra University’s geology department, stressed the need for further scientific studies into these two sites and need to conserve them.

“These two deposits are very important stratigraphy sites which are helpful in understanding how climate evolved. The ash travelled so many thousands of kilometres and was deposited at Araku. Isn’t it an important and significant site? We should at least now take steps to conserve and preserve these two sites. These ash deposit sites are usually found in river basins and valleys,” Prof. Reddy said.

He said that geo-tourism without disturbing the sites also be encouraged. “Just by looking at these two deposits one can immediately differentiate the ash from the surrounding soil. The Geological Survey of India had also identified and documented these two rare sites as belonging to Toba ash,” Prof. Reddy, who worked with GSI before joining Andhra University. told this newspaper.

A detailed study conducted by a group of researchers from the UK, France, Australia and India found that the glass shard and biotite composition of the Sagileru tephra matches that of the Young Toba Tuff from other terrestrial sites in India and from the Toba caldera, and are distinct from earlier large eruptions from Toba.

“Moreover, our survey identified rare associations between lithic artefacts and YTT deposits, making the Sagileru Valley one of the few globally identified locations with both ash and archaeology.

The identification of ash deposits and stone tool assemblages in the Sagileru Valley provides another source of information for understanding Late Pleistocene climate change, depositional environments and hominin occupations of South Asia,” said the report ‘Discovery of Youngest Toba Tuff localities in the Sagileru Valley, south India, in association with Palaeolithic industries.