On 5 Mar, 22:31, "Dave Cornwell"
wrote:
"Keith (Southend)G" wrote in message

...



On 5 Mar, 12:30, Weatherlawyer wrote:
On 5 Mar, 11:54, "Keith (Southend)G"
wrote:

http://news.bbc.co.uk/1/hi/world/europe/8550025.stm?ls

What exactly caused these waves in the Mediterranean Sea?

They occurred the day the low on the west of Iberia became the low on
the east of Iberia.

And of course you know from following the incomparably wonderful
Weatherlawyer that the low was linked to that earthquake that had been
so upsetting for everyone uik.sci.weather for the last month or so?

Note to .....

Tsunamii were called tidal waves because they are tidal. It is only
recently the badly informed have learned to think of them in terms of
height instead of volume.

Is plura plural of plural?
Bthaght! Try saying that after a plate of cauliflower cheese.

So it was the weather, not a Tsunamii cause by an earthquake?

Don't know yet but will probably find out soon as it's one of the ones I
work on doing the hygiene inspections in the summer. I'm sure they will have
a few stories to tell!

Bookmark this thread then?

Yokel wrote:

"Norman" wrote in message
...
Keith (Southend)G wrote:

| http://news.bbc.co.uk/1/hi/world/europe/8550025.stm?ls
|
| What exactly caused these waves in the Mediterranean Sea?
|
| Keith (Southend)


The wind? :-)


There was a very good documentary on this subject in the "Horizon" series a
few years back. The whole idea of these "freak" waves was discounted,
mostly by vested interests who would have had to pay more to properly design
and maintain ships, until study showed that they undoubtedly occur.

Waves can interact in various ways with each other, and also with currents
generated by tides or the overall circulation of the oceans. Under certain
circumstances energy in the general wave field can be concentrated in a few
individual members of a wave train resulting in these unexpectedly large
waves. The phenomenon is rare enough to not be obvious to those with
passing business on the seas, but not so rare that occasional incidents -
such as that reported - do not occur. Many of the allegedly "unexplained"
disappearances in the open seas are probably due to ships encountering these
"freak" waves.

When the maths and physics was done it was found that the likelihood of this
concentration of energy in individual waves increased rapidly with the
overall wave height. So under normal sea conditions one would not expect to
notice any unusual waves, but in stormy conditions they become much more
likely. The risk is also greater in areas where strong currents run, which
can also contribute energy to the waves.

So, although the energy these waves contain did come from the wind, the
waves were higher than the observed windspeed would be expected to produce
because they have "borrowed" energy from other waves in the sea around (this
is the "non-linear interaction" you will hear described in the documentary
mentioned). The cruise ship was therefore also a victim of what is best
described as "bad luck".

These waves have a high frequency of occurrence but a low frequency of
encounter. The closest parallel I can think of is the occurrence of tornadoes
in the US mid-west. These have a high frequency of occurrence yet the average
resident is never affected directly. This is because each event affects only an
infinitessimally small part of the overall area potentially at risk. Similarly,
each of these very high waves affects only an infinitessimally small part of
the ocean for a very short period of time and, therefore, almost all of them
are never encountered by a ship. Unfortunately, the media love to describe them
as "freak" waves. There's nothing "freak" about them as the can be described
scientifically. The more proper term is "abnormal" waves.

A sea state is normally described by the "significant wave height". This is
defined as the average height of the one-third highest waves in the seastate.
In any seastate occasional individual waves up to around double the height of
the significant wave height can be expected to occur. Therefore in a 3-metre
sea state it would not be unusual to encounter occasional individual waves up
to 5-6 metres. The threshold above which individual waves are deemed to be
"abnormal" is around 2.2 times the significant wave height.

I don't know exactly where or when the recent event occurred but it wasn't
necessarily caused by an "abnormal" wave. It may have been just a typical very
large wave embedded in a very rough sea state.

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.

In article
,
"Keith (Southend)G" writes:
So it was the weather, not a Tsunamii cause by an earthquake?

Since the Med is almost completely land-locked, I would think that only
an earthquake under the Med itself could cause a tsunami, and I would
have expected to see news reports about such an event if it had
happened. A tsunami in the Med would also presumably had impacted on the
coasts bordering it.
--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)

SNIP

Unfortunately, the media love to describe them
as "freak" waves. There's nothing "freak" about them as the can be described
scientifically. The more proper term is "abnormal" waves.

Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.- Hide quoted text -


'Freak' is one of the media's favourite terms. Every time someone is
swept off a rock or pier in Cornwall, it's a 'freak' wave, and more
should be done to stop people getting remotely near them. (Surely if
it was freak, we needn't worry about it happening again?) Nothing at
all to do with people running to & fro trying to avoid them (Which is
great fun of course - see pics at bottom of page
http://www.easterling.freeserve.co.uk/wpage9.html - even when you're
old enough to know better).

Graham
Penzance

On 06/03/10 11:47, Graham Easterling wrote:
SNIP

Unfortunately, the media love to describe them
as "freak" waves. There's nothing "freak" about them as the can be described
scientifically. The more proper term is "abnormal" waves.

Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.- Hide quoted text -


'Freak' is one of the media's favourite terms. Every time someone is
swept off a rock or pier in Cornwall, it's a 'freak' wave, and more
should be done to stop people getting remotely near them. (Surely if
it was freak, we needn't worry about it happening again?) Nothing at
all to do with people running to & fro trying to avoid them (Which is
great fun of course - see pics at bottom of page
http://www.easterling.freeserve.co.uk/wpage9.html - even when you're
old enough to know better).


Over forty years ago, I worked in the Marine Division of the Met Office
and remember hearing chat of the "seventh wave", which would hardly rate
as a freak occurrence. ;-)


--
Graham P Davis, Bracknell, Berks., UK. E-mail: newsman not newsboy
"I wear the cheese. It does not wear me."

"John Hall" wrote in message
...
In article
,
"Keith (Southend)G" writes:
So it was the weather, not a Tsunamii cause by an earthquake?

Since the Med is almost completely land-locked, I would think that only
an earthquake under the Med itself could cause a tsunami, and I would
have expected to see news reports about such an event if it had
happened. A tsunami in the Med would also presumably had impacted on the
coasts bordering it.
--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)


When the Greek volcanic Island of Santorini erupted circa 1650-1600 BC that
caused a series of giant tsunamis around 20 odd meters high. It is
considered to have devastaed the Minoian civilisation beyound the point of
recovery.

In article ,
says...
When the Greek volcanic Island of Santorini erupted circa 1650-1600 BC that
caused a series of giant tsunamis around 20 odd meters high. It is
considered to have devastaed the Minoian civilisation beyound the point of
recovery.



Yes. I think it was noticed and commented on at the time.

--
Alan LeHun

On Sat, 6 Mar 2010 10:55:13 +0000, John Hall
wrote:

So it was the weather, not a Tsunamii cause by an earthquake?

Since the Med is almost completely land-locked, I would think that only
an earthquake under the Med itself could cause a tsunami, and I would
have expected to see news reports about such an event if it had
happened. A tsunami in the Med would also presumably had impacted on the
coasts bordering it.

And they have this weird habit of not building & breaking & wreaking
havoc on cruise ships in deep water. That's the tipoff.

On Sat, 06 Mar 2010 07:41:22 -0800, David Oberman
wrote:

On Sat, 6 Mar 2010 10:55:13 +0000, John Hall
wrote:

So it was the weather, not a Tsunamii cause by an earthquake?

Since the Med is almost completely land-locked, I would think that only
an earthquake under the Med itself could cause a tsunami, and I would
have expected to see news reports about such an event if it had
happened. A tsunami in the Med would also presumably had impacted on the
coasts bordering it.

And they have this weird habit of not building & breaking & wreaking
havoc on cruise ships in deep water. That's the tipoff.

Rogue waves. They were once thought to be a myth by the
scientific community. But see
http://en.wikipedia.org/wiki/Rogue_waves

--
************* DAVE HATUNEN ) *************
* Tucson Arizona, out where the cacti grow *
* My typos & mispellings are intentional copyright traps *

On Sat, 06 Mar 2010 09:08:19 -0800, The Other Guy
wrote:

The ship was NOT hit by a tsunami. Even if there HAD been a tsunami,
a ship at sea wouldn't have even felt it).

I would love to be on a boat in deep water whilst a tsunami passed
under. I would imagine that there is an unnoticeable swell upward (by
perhaps a few inches) -- undistinguishable from the general surface
swell -- which, owing to the enormous wavelength, doesn't subside for
perhaps twenty or thirty minutes.

There were some eyewitness accounts published years ago of military
men on a submarine who happened to be close to the bottom of deep
water when a tsunami was propagating. They say they saw sediment
stirred up for fifteen or twenty minutes, not knowing what was causing
this.