On Tue, 4 Jan 2005 09:11:41 -0000, Charlie Pridham wrote:

Lots of people have said that, but it seems unlikely. To create a tsunami
requires a high energy shock wave, a bit of land falling in would, however
large not be moving fast enough for the damage to be transmitted any
distance, although there would certainly be a large wave locally much as
when large icebergs break off.

Rubbish. The speed of rock falling determines the wavelength of the wave,
this would determine wether it travels more or less straight or would be
diffracted around land masses.
We are talking somewhat bigger bits of rock than icebergs dropping off a
glacier in to the sea.

Issue 2259 of New Scientist magazine, 07 October 2000:
"It's hard to imagine what would happen if half a trillion tonnes of rock
slid into the sea. But Hermann Fritz, a PhD student at the Swiss Federal
Institute of Technology in Zurich, has spent several years modelling how
landslides generate waves when they fall into water. Earlier this year, he
constructed a lab model of the western flank of the Cumbre Vieja in a wave
tank. The model is an elongated wedge-shaped block resting on a 10-degree
slope with the tip of the block lying just under the water. When the block
is released, it slides down the slope generating a wave, which is recorded
by a high-speed camera.

Fritz found that the sliding block generated a long, shallow, fast-moving
wave¡Xthe classic profile of a tsunami. Scaling up 10,000 times, the model
predicts that in real life the crest of the wave generated by the collapse
of the western flank of the Cumbre Vieja would initially be a staggering
650 metres above normal sea level, more than enough to submerge the tallest
building in the world. Fritz admits that there is a big size difference
between his model and the real tsunami, but he has no doubt that the
dimensions of the wave are in the right ballpark."


and


NS 29 August 2001:
"When the La Palma volcano caves in, Ward says it will trigger a series of
around ten waves, spaced about a hundred kilometres apart. As they reach
the shallow water near the North American coast, they will build up to
about 50 metres high, enough to travel several kilometres inland. "There's
a significantly broad danger zone," says Day.

Although the volcano's unstable flank points directly towards North
America, it is not just North Americans who should be worried. Day
originally estimated that the collapse would create a shockwave travelling
in a straight line across the Atlantic, directly towards America's East
Coast. This would happen if the speed of the landslide was faster than the
speed of the waves in deep water.

But the model shows that the landslide will actually move at around 100
metres per second, about two-thirds as fast as the waves in the water. This
means the tsunamis will spread out in an arc.

Shallower water near La Palma would then slow the waves down, forcing them
to curl around towards northern Africa and northern Europe, even behind La
Palma on the Spanish coast."

More at Geophysical Research Letters (vol 28, p 3397)

--
Tim C.