By Sid Perkins
Field studies of an Indonesian coastline ravaged by a tsunami in December 2004 suggest that leaving mangrove forests intact along a shoreline could substantially reduce damage from moderate-sized tsunamis.
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When a magnitude 9.1 earthquake struck west of Sumatra on December 26, 2004, it spawned a tsunami that hammered nations fringing the Indian Ocean (SN: 1/8/05, p. 19). Near Banda Aceh, Indonesia, on the northwestern tip of Sumatra, the tsunami swept inland more than 4 kilometers and killed tens of thousands of people. Now, by studying wave-induced damage to the mangrove forests surrounding that city, civil engineer Shunichi Koshimura of Tohoku University in Sendai, Japan, and his colleagues have developed a model to estimate the tsunami-buffering capacity of intact mangrove forests. They report their findings online June 30 in the Journal of Geophysical Research–Oceans.
About two years after the damage occurred, the researchers took measurements of almost 700 mangrove trees in five broad swaths of intertidal terrain where dense stands of those trees — from the genus Rhizophora — had stood before the tsunami struck. Many of those trees were damaged, snapped off near their bases by the surging water, but some had survived the inundation unscathed. The team’s analyses showed that as the estimated wave-induced stresses on tree trunks increased, the proportion of damaged trees also increased.