"Sacha" wrote in message
k...
On 3/1/05 11:30, in article , "Cerumen"
wrote:


wrote in message
...
On Sun, 2 Jan 2005 16:09:33 -0000, "Bob Hobden"
wrote:

The main risk is the big piece of rock which is expected to fall
off
an island in the Canaries, generate a tidal wave that will wipe
out
the East Coats of the USA and not do a lot of good to the low
countries.

Apparently a tsunami hit the west coast of Ireland in 1775 ? after
a
seismic event near the Azores and Canaries causing some
considerable
damage..

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!)

As well as New York

Franz

"Franz Heymann" wrote in message
...

"Sacha" wrote in message
k...
On 3/1/05 11:30, in article , "Cerumen"
wrote:


wrote in message
...
On Sun, 2 Jan 2005 16:09:33 -0000, "Bob Hobden"
wrote:

The main risk is the big piece of rock which is expected to fall
off
an island in the Canaries, generate a tidal wave that will wipe
out
the East Coats of the USA and not do a lot of good to the low
countries.

Apparently a tsunami hit the west coast of Ireland in 1775 ? after
a
seismic event near the Azores and Canaries causing some
considerable
damage..

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!)

As well as New York

Franz

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.

--
Charlie, gardening in Cornwall.
http://www.roselandhouse.co.uk
Holders of National Plant Collection of Clematis viticella (cvs)

Charlie wrote:
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

This is contentious. Have you read
http://www.benfieldhrc.org/CentreNew...es/tsunami.htm or
http://www.bbc.co.uk/science/horizon...anscript.shtml

More recent suggestions that it would break up before falling, and
"only" cause a wave 2 to 3m high have been made:
http://news.bbc.co.uk/1/hi/sci/tech/3963563.stm . That page has links
to sites that support and oppose the original tale.
It boils down to "we can't know the future".

On 4/1/05 9:11, in article ,
"Charlie Pridham" wrote:
snip

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.

But isn't the chunk of La Palma predicted to fall into the sea following
volcanic action?
--
Sacha
www.hillhousenursery.co.uk
South Devon
(remove the weeds to email me)

On Tue, 04 Jan 2005 10:01:05 +0000, Sacha wrote:

On 4/1/05 9:11, in article ,
"Charlie Pridham" wrote:
snip

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.

But isn't the chunk of La Palma predicted to fall into the sea following
volcanic action?

Yes, but the eruption may not need to be vary large, just the right sort
that lets water in behind the slipping section.
--
Tim C.

"Sacha" wrote in message
k...
On 4/1/05 9:11, in article
,
"Charlie Pridham" wrote:
snip

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.

But isn't the chunk of La Palma predicted to fall into the sea
following
volcanic action?

Not necessarily. It is said that a really severe rainstorm might do
the trick It is already making small but ominous movements now , and
the lubrication provided by filling the cracks with water might just
trigger the lot to slip off.. There is no doubt that it will fall
into the sea some time. The real unanswerable question is whether it
will slide off in one fell swoop or piecemeal.

Franz

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.

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

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

--
Charlie, gardening in Cornwall.
http://www.roselandhouse.co.uk
Holders of National Plant Collection of Clematis viticella (cvs)

"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

"Charlie Pridham" wrote in message
...

"Franz Heymann" wrote in message
...

"Sacha" wrote in message
k...
On 3/1/05 11:30, in article ,
"Cerumen"
wrote:


wrote in message
...
On Sun, 2 Jan 2005 16:09:33 -0000, "Bob Hobden"

wrote:

The main risk is the big piece of rock which is expected to
fall
off
an island in the Canaries, generate a tidal wave that will
wipe
out
the East Coats of the USA and not do a lot of good to the low
countries.

Apparently a tsunami hit the west coast of Ireland in 1775 ?
after
a
seismic event near the Azores and Canaries causing some
considerable
damage..

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!)

As well as New York

Franz

Lots of people have said that, but it seems unlikely.

I am afraid that if the whole chunk og rock comes adrift in one go, it
is a dead cert. It is only a matter of when.

To create a tsunami
requires a high energy shock wave,

No. That is not so. Any large, localised disturbance will do the
trick.

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 would rather listen to the physicists who have done the
calculations. They actually do know the magnitude of the wave which
would occur if the whole cracked chunk of rock fell into the ocean in
one go.
In a deep ocean with a flat bottom, a tsunami is actually a relatively
slow, stately occurrence. All hell begins to break loose when it
reaches a sloping shoreline.

Franz