"Charlie Pridham" wrote in message
...

"Dave" wrote in message
...
A recent article I read somewhere said that if the predicted
bit of
La Palma
falls off in one slab the resulting tsunami will lead to the
disappearance
of the Isles of Scilly (among other damage!)
Charlie Pridham writes

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.

I think you confuse speed with energy. If you drop a very very
large
mass (say 5000 million tons) a few hundred feet (and I think in
the case
of the canaries it drops a long way down to the ocean floor) then
the
*energy* released is converted into a (relatively) smaller mass of
water
travelling *very* fast. I don't know what the conversion factor is
but
say 1% of the mass travelling at say 20 times the speed would
still be
quite significant.
--
David
I may be wrong but I am not confused! :~) once the rock mass was in
the
water the effect would be slight however far it falls, it can after
all only
fall and accelerate at 9.81m/s2 .

That is quite wrong. The rock hits the water quite fast, with a large
amount of energy. As it sinks in the water, it gives its enrergy to
the water, spreadover a large range in depths. These are just what is
neded to excite a deep water wave.

and I still think you would be hard
pressed to even detect it in New York

You could not be more wrong on this issue if you tried.
Please desist from making qualitative speculations from the side
lines. As has been said before, there are actually model experiments
being performed under conditions where the scaling laws are known.
The results from those are more important than your wishful thinking.

were it to happen, (a similar sized
lump arriving from space would be travelling at a much higher speed
and
would indeed cause allsorts of problems were it to hit ocean).

The movement
of a tectonic plate can in some instances be at very high speed

coupled with
the total mass on the move gives a huge amount more energy and even
then not
all underwater quakes produces these waves.

Franz