Monster waves tracked from space
17 May 2007
Reunion Island in the Indian Ocean is everyone’s idea of a tropical paradise. However, on 12 May 2007, the beautiful tourist spot was lashed by waves up to 11 metres high. The crashing surf caused chaos and devastation, with two fishermen missing, several collapsed piers and flooding of homes and hotels.
The events leading up to this destruction have been recorded by a radar instrument on board ESA’s Envisat satellite. This instrument bounces radio signals off the sea surface and picks up the echoes. These echoes tell scientists the size, height and speed of the waves. In the case of the Reunion flooding, Envisat showed that the waves came from a large storm in the south Atlantic. Over the next three days they spread away from the storm centre. Some waves travelled north east for nearly 4000 km before slamming into Reunion.
Although waves were forecast to hit the island, they were generally expected to be only a couple of metres high. However, analysis of Envisat data shows that the waves were about 5 metres high and widely spaced in the open sea. A long gap between waves is a sign that they were caused by storm force winds. Approaching the coastline, the waves slowed down and doubled in height.
"Swells are still surprise factors, which can unfortunately be deadly," said Bertrand Chapron of IFREMER, the French Research Institute for Exploitation of the Sea. "In the near future we anticipate using SAR (space radar) wave data to predict their arrival time and intensity."
