Written by Bella Dalima
12 Dec, 2013 | 4:30 pm
A cave on the northwestern coast of Sumatra holds a remarkable record of big tsunamis in the Indian Ocean. The limestone opening, close to Banda Aceh, retains the sandy deposits washed ashore by huge, earthquake-induced waves over thousands of years.
Scientists are using the site to help determine the frequency of catastrophes like the event of 26 December 2004. This is being done by dating the cave’s tsunami-borne sediments, which are easy to see between layers of bat droppings.
The investigations are ongoing but the team thinks it can see deposition from perhaps 7-10 tsunamis. The geometry of the cave means these events would likely have been generated by earthquakes of Magnitude 8, or more. By way of comparison, the devastation wrought by 26 December 2004 stemmed from a M9.2 tremor.
Dating the old deposits is obtained by radiocarbon analysis of organic debris caught up in the bands, such as molluscs and pieces of charcoal from old human-lit fires.
Work is under way to date even the insect remains eaten by the bats and now immersed in the guano layers.
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