Sediment cores reveal regional history of tsunamis

Economist : Knowing that a coastal region has been hit by tsunamis in the past, and how frequently, is important for preparing for potential future strikes. A team led by Harvey Kelsey of Humboldt State University in California has found that evidence of past tsunamis can be found in sediment cores taken near shorelines. The researchers took cores from the Aceh region of Indonesia, which was seriously hit by a tsunami in December 2004 . Before the tsunami, the region was heavily covered by mangrove forests. The top of the sediment core consisted of loose sand deposited by the tsunami. Just below it was a layer of soil rich in mangrove pollen and small fossilized animals known as foraminifera . Deeper in the core, that pattern was repeated several times, revealing that three more tsunamis had occurred within the last 8000 years. Layers of sand on top of sand indicated that even more tsunamis struck before the mangrove forests grew back. Kelsey’s group believes that similar analysis of coastal sediment cores from other regions could reveal their level of tsunami risk.