THE survivors of a tsunami that killed thousands living on the shores of the Mediterranean in AD 365 called it the 鈥渄ay of horror鈥�. Worryingly, history may be due to repeat itself, say geologists who have located the source of the wave.
No one had been able to find evidence pinpointing the earthquake that caused the tsunami, which washed into the Egyptian city of Alexandria and the Nile delta. The mainstream view was that a series of quakes had struck the region 鈥� cumulatively thrusting a section of western Crete upwards by 10 metres.
Beth Shaw and colleagues at the University of Cambridge carbon-dated a section of corals on the coast of Crete that were lifted clear of the water during the upheavals. The corals鈥� distribution and identical age showed that one giant quake must have lifted all of them by 10 metres in one massive push 鈥� revealing the tsunami鈥檚 source.
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鈥淭he corals鈥� distribution and age revealed that one giant quake must have lifted all of them 10 metres in one massive push鈥�
The only thing that could have generated such a large uplift at that location is an earthquake in a steep fault in the Hellenic trench, near Crete, says Shaw. The team built a computer model which suggested such movement would have created a 2-metre wave in open water 鈥� the same height as that generated by the Sumatran earthquake in 2004 鈥� which would have reached the African shore (Nature Geoscience, ).
Shaw says a further slip in the part of the fault that caused the tsunami is only likely to happen once every 5000 years. However, other segments of the fault may slip on a similar scale, she says, and this movement could happen every 800 years or so. 鈥淭he big unknown is whether the fault that slipped is unique, or one of many contiguous patches that might slip in the future,鈥� says Roger Bilham of the University of Colorado in Boulder.
In another new study, Anja Scheffers at Southern Cross University in Lismore, New South Wales, Australia, and colleagues reveal geological evidence of five tsunamis that hit Greece over the past 2000 years. Most were small and local, but in 1303 a larger one hit Crete, Rhodes, Alexandria and Acre in Israel (Earth and Planetary Science Letters, ).
