Giant Tidal Wave in Thailand.....

Lee Bell wrote:

> Since we know of the deaths and devastation caused by these waves, it's easy
> to say that they are not trivial. On the other hand, we've all seen
> pictures of people surfing on waves of comparable height. It's not clear
> why a Tsunami is so different, but it's apparent that they were.

The speed. Let your belly be hit by one liter of water travelling at 200
mph.
Matthias

On Mon, 27 Dec 2004 12:23:49 -0500, Mike Ross <mike@corestore.org>
wrote:

>On Mon, 27 Dec 2004 14:08:41 GMT, "Lee Bell"
><leebell@ix.remove.netcom.com> wrote:
>
>>>> Large is relative. A 20' wave still isn't trivial.
>>>>
>>> To say the least, Alan. I do not know the physics of wave energy, but I
>>> remember reading that a 4' wave on one mile of coast generates 35,000 hp
>>> of energy. I'm sure that is logarithmic with a 20' wave.
>>
>>Since we know of the deaths and devastation caused by these waves, it's easy
>>to say that they are not trivial. On the other hand, we've all seen
>>pictures of people surfing on waves of comparable height. It's not clear
>>why a Tsunami is so different, but it's apparent that they were.
>
>OK.
>
>Normal waves:
>
>------/\---/\---/\----
>
>Go up, down, up, down - individual waves may be (say) 20' from crest
>to trough and 50' long from one crest to the next.
>
>Tsunami:
>
> --------- (a mile or more) --------
> / \
>-------- -------------
>
>It's not really a 'wave' at all, as we normally think of waves - it's
>a huge mass of displaced water. It's much more like the storm surge
>beneath the eye of a hurricane, to give a more familiar example, which
>is when the surface of the ocean is 'sucked up' by the low pressure in
>the eye. Except the tsunami is much worse, as it arrives all at once,
>not gradually building up over hours like an approaching hurricane.
>
>Think 'instant temporary global warming raising water level by 20' or
>more'.
>
>Mike

It seems to me that the difference might be that the tsunami wave is
generated from the ocean bottom and displaces water throughout the
water column leaving no room for backwash (undertow?) and the force
pushes all the water in the water column ahead of it so it piles up
big time. This is as opposed to wind generated waves which affect
primarily the surface water and allow some backwash underneath the
surface.

I have no idea at what point friction starts to have an appreciable
effect and begins to dissipate the force at depth but I can imagine
there's a huge difference in behaviour between storm driven waves and
bottom displacement generated waves.

JF

Lee Bell wrote:
>>>? >Tidal waves as high as five metres hit Penang and several other
>>>? >Malaysian islands following the 8.9-magnitude earthquake near
>>>? >Indonesia's Sumatra island.
>>>?
>>>? So what's a 5-6m tsunami wave like compared to a regular one? And is
>>>it
>>>? a one shot deal, or does it come in a set?
>>>?
>>>? For one of the largest earthquakes ever, I guess I thought it would be
>>>much bigger.
>>>
>>>Large is relative. A 20' wave still isn't trivial.
>>>
>>
>>To say the least, Alan. I do not know the physics of wave energy, but I
>>remember reading that a 4' wave on one mile of coast generates 35,000 hp
>>of energy. I'm sure that is logarithmic with a 20' wave.
>
>
> Since we know of the deaths and devastation caused by these waves, it's easy
> to say that they are not trivial. On the other hand, we've all seen
> pictures of people surfing on waves of comparable height. It's not clear
> why a Tsunami is so different, but it's apparent that they were.
>
> Lee
>
>

Lee,

First, the speed that the waves are travelling (much greater) means that
they hit the coast with much more energy. Second, the waves are from one
end of the horizon to the other, and not caused by local topography. So
they hit in areas not normally subject to such large waves. Of course,
in these areas that are normally safe from large waves ... this is where
us smart humans decide to build resorts, fishing villages, etc. Thus the
result.

I don't want to trivialize the disaster. These things can seem beyond
comprehension. However, land use planners will tell you that it is
predictable that they will occur, although you never know exactly when.
The where is more certain. The Japanese have warning systems in place -
they know through past experience that certain cities are vulnerable.

The majority of human civilization developed in coastal areas, and the
concentration is still there. So long as we build in flood plains and
along coast lines, then hurricanes, floods, tsunamis and erosion will
continue to wreak havoc.

Bart F.

In article <95e8b$41d01698$ce504905$23039@allthenewsgroups.co m>, Joe English
<jenglish@wisperhome.com> writes:

>Ound what to send

Huh?

In article <cqov8k$2te8$1@agate.berkeley.edu>, jor@soda.csua.berkeley.edu
(Jason O'Rourke) writes:

>but I'm not so concerned with the energy of a 4' wave over a mile of coast.
>Ocean Beach just down the road from me has surfing ranging from nothing to
>double overheaders. And occasionally bigger waves that aren't surfed. A
>storm
>can give us 20'ers for a while. Doesn't harm things a bit...the coast is
>forged
>by this range. Personally I've been out in up to 10s, though usually not
>intentionally about 6-7.
>
>This one wiped out beach resorts, so obviously it's more than that.

Wondering . . .what would Scuba divers experience in these conditions? Would
the biggest worry be "being thrown onto land at great force?" Or worse?

"Fishbre396" wrote ...
> Perhaps, education about the result of Tsunamis
> is in order?

Uhhh... I believe that is what they just had...

Mike Ross <mike@corestore.org> wrote:
>OK.
>
>Normal waves:
>
>------/\---/\---/\----
>
>Go up, down, up, down - individual waves may be (say) 20' from crest
>to trough and 50' long from one crest to the next.
>
>Tsunami:
>
> --------- (a mile or more) --------
> / \
>-------- -------------
>
>It's not really a 'wave' at all, as we normally think of waves - it's
>a huge mass of displaced water. It's much more like the storm surge
>beneath the eye of a hurricane, to give a more familiar example, which

Nice ASCII art!
--
Jason O'Rourke www.jor.com

Joe English <jenglish@wisperhome.com> wrote:
>
> How much time passed from the earthquake to the Tsunami?

In some areas, not all that much time at all. The quake hit at 7:59am
local time. Reportedly 33 minutes later, it hit the coastal region of
Aceh in Sumatra. Phuket appears to have been hit within the first hour.

Generally speaking, the delay times were slightly more than the nominal
maximum deepwater speed of a Tsunami of 500mph. Thus, a location 1500
miles away would be hit no earlier than 3 hours after the quake. This
is enough time to issue a warning if you have the technology in place,
but in 3rd World types of areas, its unlikely that you'll be able to
successfully disseminate a warning.

FWIW, the Tsnunami was detected on tidal gages 5,000 miles away in New
Zealand, approximately 17 hours after quake (= 300mph average velocity).
Fortunately, it was only 4"-12" in height, probably in no small part
because it had to dissipatively warp around Australia to get there. It
should theoretically have also been detectable in the Atlantic too.



> You would think that they knew it was coming from aerial
> surveillance of the area.

It is rare to see what you weren't even looking for.

The Pacific basin has a detect/warning system, because ~95% of all known
Tsunami's occur there. The Indian Ocean basin doesn't have such a
network, nor does the Atlantic Ocean.

The effective fallback system is a Siesmologist somewhere whose
equipment detects the quake, which then gets plotted to an undersea
location, and some deductive reasoning says to make some phone calls.
Yesterday's news reports alluded to some warning phone calls being
initiated, but lacking a "hot line", it would have gotten bogged down.
I did see one news report that claimed that at least one of the resort
hotels somewhere did try to evacuate their beach before the wave hit.


> Does/Can a tsunami be generated from the epicenter or miles away or
> just anywhere in the general area?

I believe that it has to generally be near the epicenter, as the basic
cause is that the ground has shifted, and the water over that location
is raised in elevation, so it starts to flow downhill (away).



-hh

On Mon, 27 Dec 2004 08:19:52 -0600, Joe English wrote:


> Wasn't Mossman going to Thailand to dive over XMAS? Does anyone
> remember or know?

http://groups-beta.google.com/group/...14c240ecf1fddf

"Reef Fish" wrote ...
> I suspect diving in Indonesia and the Maldives will be forever changed
> by this natural disaster.

Uhhh.... New wreck dives? <sick-grin>