Bat cave provides clues to past tsunamis

BBC : A cave in Sumatra and its bat inhabitants are providing researchers with a remarkable record of the large tsunamis that have occurred in the Indian Ocean over the past 7500 years. Because the Acehnese cave lies at least 100 m from the coast and its entrance is raised, only severe storm surges such as tsunamis can get in. The tsunamis deposit sandy sediments that include such marine organisms as Foraminifera and molluscs. Meanwhile, bats living in the cave cover the sediment layers with their droppings, which contain insect remains. The alternating layers of material create a rich stratigraphy, from which the researchers have been able to determine the number and spacing of the biggest tsunamis over time. They have learned that tsunamis have no discernible pattern: There can be long periods with no activity, and there can be multiple events in a single century.