Posted on 01/13/2005 1:32:01 AM PST by Cincinatus' Wife
The destructive waves triggered by the Boxing Day earthquake tore across the Indian Ocean at 800kmh, the US space agency NASA has confirmed.
As the waves reached the shallow waters of Sumatra and Sri Lanka they slowed, but their heights grew dramatically, from centimetres to "walls of water up to 10 metres high".
The agency revealed that two waves, 800 kilometres apart, were detected by two joint NASA and French satellites - named Jason and Topex/Poseidon - passing over the Bay of Bengal about 150 kilometres apart, two hours after the quake.
As a result, the exact speed and size of the tsunami are no longer a matter of scientific speculation.
The first wave, when spotted 1200 kilometres south of Sri Lanka, was 90 centimetres tall from the top of its leading crest to the bottom of the following trough. The crest was 50 centimetres above the normal sea height recorded several weeks earlier, while the trough was 40 centimetres below normal.
"The distance from one wave crest to the next was about 800 kilometres. The first wave was followed by a second with a crest height of 40 centimetres above normal.
Near the northern end of the Bay of Bengal "two waves with crest heights of 40 centimetres and 20 centimetres above normal were approaching the coasts of Myanmar [Burma]. Spreading across the Bay of Bengal from the earthquake zone offshore from Western Sumatra, these tsunami waves eventually reached shallow waters along the coasts of Sumatra, Sri Lanka, Thailand and Southern India.
"Their open ocean speeds reduced from that of a jet plane, 800kmh, to about 32kmh."
But as they slowed they turned into "walls of water up to 10 metres high with great destructive power".
Jason and Topex/Poseidon were launched to measure sea heights to help scientists understand ocean circulation and its effect on the world's climate.
It was the first time large tsunami had been observed and measured from space.
"These two satellites make only about 13 Earth revolutions daily," said NASA's Philip Callahan, who has been looking for tsunami observations since Jason was put into orbit in 1992.
"There is a very low probability of capturing observations in any given location within two hours of an event like this. The fact that Jason captured the tsunami's signals is serendipitous, but is nevertheless a major boon for oceanographers."
Just WOW....
Over 30 feet high.
Yowsa!
Yeah, when it got to shore. Over the open ocean.... I wonder if there are any reports of what it felt like. Big ol speed bump.
When first detected the waves are about 18 - 24 inches? How in the world can they tell the difference between that wave and normal waves of the same basic height?
OK. thx
I still don't understand how it could travel so fast.
There are 2.54 cm in an inch. They two waves were only 16" and 8" over deep water. Even more amazing they could be detected from a satellite.
WOW. That'd be about 500 mph. What a ride. Surf's up! LOL.
Seriously though, I had been wondering how long it took these waves to reach land but I never imagined that kind of speed.
Don't ask me! That's why I was wondering about any reports of what it must have been like to actually experience it over open water.
These satellites use a laser retroreflector array to measure the sea height to within 1.7 inches.
Because they're incredibly wide. It still takes a lot of processing power and analysis to separate out the noise. The tsunami waves are 18-24 inches high and miles wide.
When water gets warm it also bulges up; when there's a powerful El Nino it causes the sea surface to rise in the Eastern Pacific; these satellites were designed to monitor things like that; when you see an El Nino shot of the Pacific on TV it's usually from these satellites.
Remember there are no individual water molecules moving that fast; water didn't move from Sumatra to India at that speed; the WAVE did. The wave is a disturbance propagating, not actual water moving, when it's in deep water.
The survey reports from Thailand are done (may be months before they come in from other areas) and at Khao Lak in Thailand the maximum height was 10.72 meters. It was lower at Phuket and Phi Phi, around 4-6 meters.
I suspect Banda Aceh will have much higher final heights.
Glad everyone was ok. This will keep me praying never to get 'sideways'!
Yeah, when it got to shore. Over the open ocean.... I wonder if there are any reports of what it felt like. Big ol speed bump.
Actually I read that you don't see or feel anything in the open water. The wave is like any other wave...its when it reaches shallow waters do you see its true nature.
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