Tsunami measurements, by satellite

THE Indian Ocean tsunami had reached heights of up to 33ft (10m) when it crashed ashore on Boxing Day, satellite images have revealed.

The measurements come from American and French oceanography satellites that passed over the Bay of Bengal two hours after the magnitude 9 earthquake struck southwest of Sumatra and observed a tsunami for the first time. . .

In the open ocean the crest of the tsunami wave stood 20in above the norm and was followed by a trough 16in below the norm.

The satellites can detect ocean surface perturbation down to a resolution of some 5 to 10 cm (2 to 4 inches), according to the NOAA site linked below.

When the wave reached the coast, however, the shallow water caused it to slow from 500mph to about 20mph, and to rear up into a wall of water up to 33ft high.

Full NOAA release here, with images and video.

Not entirely relevant aside: A friend recently had a bit of a fit over his daughter's teacher calling a tsunami a "tidal wave". "Tsunami" has been the preferred term for some time now, but after having seen some of the videos from Thailand I can see how "tidal wave" isn't such a misnomer. A normal wave is a pulse of energy thrown up on the shore; it comes, it breaks, it's gone. Nothing like that massive sea in the videos, piling into the shore and coming on and on and on, the ocean's entire surface suddenly raised impossibly high. Its cause may not be tidal, but what else so well describes that awesome displacement?

Posted by David on January 13, 2005 2:49 PM