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Tsunami 'trigger' spotted

"Earthquakes are common in the [Carribbean] area and we are pretty sure it's going to go soon."

Spotting risky rock formations that are about to collapse and trigger tsunamis could be done with the help of Google Earth, new research suggests. The software could prove a useful tool where other types of survey prove too difficult or expensive.

One such spot has just been found in the Caribbean by Richard Teeuw from the Geohazard Research Centre at the University of Portsmouth, UK.

"We were doing fieldwork on the volcanic island of Dominica in the Lesser Antilles and initially just used Google Earth to identify good study areas," he says. "But with its 3D flyover tool, we quickly got excellent direct glimpses of a slab or rock that may soon cause a tsunami."

The flyover tool allowed Teeuw and his colleagues to examine the million-tonne rock in 3D, and from several angles. They found plenty of evidence that this block of coastline is a landslide waiting to happen. "The flank is undercut by erosion from the sea and we saw scars from recent landslides and tension cracks above the block," he says. "Earthquakes are common in the area and we are pretty sure it's going to go soon."

The researchers have calculated that when the rock tumbles into the sea, it could trigger a tsunami of up to 3 metres high. Though that is smaller than the waves of the 2004 Boxing Day Tsunami, the coast of the island Guadeloupe is only 40 kilometres away and has vulnerable flat beaches.

"If even a small tsunami hit during the tourist season, and people were unprepared, the impact could be quite bad," says Teeuw. What's more, if other blocks above the problem slab were destabilised by a larger earthquake or movement of the slab itself, a much larger tsunami could result.

Teeuw says that the Google Earth images give enough reason to examine the area more closely with high-resolution survey techniques, such as laser altimetry, which would more accurately appraise the risks of a potential collapse.

Surveys of this kind are too expensive to use for routine scans over large areas, especially in poor countries. "If we can do a systematic study using Google Earth to identify the areas most at risk, the detailed analysis can be focused only on the spots that really need it," he says.

Journal reference: EOS (volume 90, number 10, page 81)