beautiful monsters: mega-tsunami

January 03, 2005


Carla has a wrap up of historic earthquakes, some of which caused tsunami. Apparently, though, some of the biggest tsunami aren't caused by earthquakes at all.

Pre-human-history there were sometimes mega tsunami caused by the collapse of volcanic islands. They’ve worked out that a certain kind of volcano is built of very porous material that the rainwater soaks into, combined with walls of hardened lava that act as dams. Apparently if you take a mountain filled with water, and then add the heat of an eruption, the water pressure builds up and the mountain falls apart. There’s one that they reckon will collapse sometime in the next few hundred years. The volcano is called Cumbre Vieja, the island is La Palma, in the Canary islands. They have no idea when it might collapse. They can predict that initial wave heights will be 900m. These would drop to 50-100m by the time they reached the African mainland. 15-25 meter waves would hit the east coast of North America 8-9 hours later.

The highest tsunami wave ever recorded was caused by a landslide in Lituya Bay, Alaska in 1958. A wave more than 500 m high stripped trees and soil from the steep walls of a fjord. It dissipated quickly upon reaching the sea.

There's a theory that the great flood (present in the bible and stories from other cultures) may have been a tsunami. And of course the theory that the dinosaurs were wiped out by a mega-tsunami caused by an asteroid.

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