Theoretical explanations of damage from tsunamis are ignoring the destructive force of the sediment that the huge waves stir up before coming ashore, a German scientist said Friday. Heinrich Bahlburg of the University of Muenster said he had discovered that up to 30 per cent of the floodwater was sand and silt. The slurry put more strain on buildings and land than pure water. Professor Bahlburg and a colleague, Robert Weiss, took soil and sand samples three months later at places where the tsunami from the December 26, 2004 great Sumatra earthquake struck Pondicherry, India and Malindi, Kenya. "At Pondicherry, the sea rose about three and a half meters," said Bahlburg at the university in northern Germany. The geologist said existing scientific models treated a tsunami as pure water. He argued that the destructive force could not be read just from the wave form or height of flooding, but also had to take account of the amount and type of sediment carried ashore. "You can't prevent a tsunami, but we can help to make more realistic predictions to design coastal protection and warn more accurately," he said. A tsunami is a series or "train", of high waves caused by an undersea earthquake. Unlike surf, with a time between crests of five to 20 seconds, tsunami periods are usually between five minutes and an hour with the water often receding from shore and then flooding the land.
