Art Mosher wrote:

Curiosity? Should not the Tsunami wave affect a high seas cruising
boat? I have seen no mention of it anywhere; but would have thought
there would be some damage to boats at sea. ??

- Art


Art,

We who live in boats, live on the boundary zone between water and air
where water shows it's most interesting effects. Intuitively you are
correct, we stand the chance of feeling the effect but it is mitigated
by water's ability to translate the wave from horizontal to vertical
which at the same time reduces it's power many fold and thus we can miss
the event with all the "background noise" already going on. Perhaps a
submarine at depth might have it's dishes rattled a little, but not so
us on the surface. It would be interesting to have someones observation
from an absolutely flat (no wind - dead) sea knowing it was about to happen.

We are most accustom to surface wind generated waves, an active subject
on this site at the moment... In these, water has both vertical and
horizontal components of motion and (most) all the energy of the wave is
contained in a shallow depth of water about equal to the scope or
peak-to-peak distance. If you look into surfing, the great spots are
places where long fetch waves are "funneled" and turned from tame smooth
rounded top seas into sharp faced monsters by gradients that turn
horizontal motion into up motion.

Tsunami waves are more characteristic of sound waves and travel by
compressibility of water (thus it's high speed) rather than surface
waves where water acts like a non-compressible liquid affected by
gravity. The tsunami energy is found all the way from near-surface to
bottom and the motion is only horizontal. The similar thing happens in
shallowing water as in the surfers best waves. Only in this case you
can make a case for the ocean "erupting" out of the bay as a visual
observation from the energy and movement being funneled by the bottom
and sides. Remember pictures of "your hard-of-hearing great great
grandpa" using that weird looking funnel stuck in his ear to hear you
better?

As the volume of water "thrust" up on shore runs back to the sea, boats
can kiss the bottom as fast flowing water recedes. We in boats can go
further down than we ever went up. Yet at anchor at depth is the place
to be as long as crud doesn't mess up our rode. It's great news that it
is a very rare event in daily living. Tsunamis even happen here on the
great lakes to much smaller extent.

It seems interesting when earthquakes energies are likened to atom
bombs. I suppose we do that to give perspective to our human ability to
release energy vs. natures ability, and to make some yardstick of
destruction as you compare war pictures of Japan. I would put good
money on this not being the first nor most destructive wave in geologic
time, but like Pompai we humans site our places to live by other
factors. My sadness for these people is deep, I pray they can put their
lives right soon, and the compassion demonstrated by the cruisers in the
neighborhood needs to be rewarded in some way. Today I hear the US
(maybe USGS or NOAA) says "there was nothing we could do even though we
knew for hours it was going to happen" so maybe these agencies need a
swift kick to change an attitude.

A fair amount of information is available on tsunamis, yet you and I
will probably spend greater effort toward understanding more likely to
happen things. I'm happy to see this will get into the cruising
publications so we can have a leg up at understanding how to avoid their
effects.

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