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gridloreThere seems to be a lot of misunderstanding about what a tsunami actually is and the danger presented by one. I've seen a lot of scoffing on local news sites about the predicted 2 to 5-foot surges, commenting that those are smaller than the normal waves seen at Ocean Beach and other popular surfing sites. True enough. Despite the name (tsunami means "harbor wave" in Japanese) we are not talking about a normal beach waves. The waves we like to play in and give surfers their reason to live are an artifact of tides, winds, the shape of the ocean floor and currents. The ocean sloshes around, and when it hits the coast the water humps up a little and forms waves. These can vary from the little breakers I loved as a kid to the beautiful and monstrous waves of the Banzai Pipeline in Hawaii.
A tsunami is created by a seismic event and is a shock wave traveling through the ocean. A big earthquake, like the one Japan just experienced, can send a compressed wall of water surging out in all directions. Changes in depth, what the ocean floor is like, water temperature, and other factors can cause this surge to weaken in areas, change direction, or even fade away. But when the tsunami reaches the coast, things get bad. Tsunamis move in open water at close to 500mph. They slow as the reach coastal waters, but this just allows more of the surge to pile up. A tsunami encountered by a ship in the open ocean may go unnoticed.
People forget that water is heavy. A cubic foot of sea water masses about 64lbs. When that tsunami reaches shore, it contains tens of thousands of cubic feet of water moving at speeds up to 200mph. Even if the actual height of the surge is only two feet, that surge will hit like a battering ram and there are tons and tons of water behind it. Plus the surge is going to pick up anything loose on the sea floor or in its path and turn those things into missiles. You have to think of a tsunami not as a wave, but as a sudden, destructive rise in sea level coupled with an amazing amount of energy directed inland.
The only smart thing to do if you are near a coast and a tsunami alert is given is run like fuck for higher ground. Gaining twenty feet could save your life. Watch some of the videos from the 2004 Boxing Day Tsunami.. none of those people saw anything out of the ordinary until the surge was right on them.
It looks like we got off light here on the North American coast. Some damage to harbors and boats, a few morons who needed to be rescued from their own folly. We're still in the danger period, so I'm keeping my eyes open. Japan wasn't so lucky.
Remember people, ours is a big, dangerous planet and the universe has no mercy. Understand the risks!
A tsunami is created by a seismic event and is a shock wave traveling through the ocean. A big earthquake, like the one Japan just experienced, can send a compressed wall of water surging out in all directions. Changes in depth, what the ocean floor is like, water temperature, and other factors can cause this surge to weaken in areas, change direction, or even fade away. But when the tsunami reaches the coast, things get bad. Tsunamis move in open water at close to 500mph. They slow as the reach coastal waters, but this just allows more of the surge to pile up. A tsunami encountered by a ship in the open ocean may go unnoticed.
People forget that water is heavy. A cubic foot of sea water masses about 64lbs. When that tsunami reaches shore, it contains tens of thousands of cubic feet of water moving at speeds up to 200mph. Even if the actual height of the surge is only two feet, that surge will hit like a battering ram and there are tons and tons of water behind it. Plus the surge is going to pick up anything loose on the sea floor or in its path and turn those things into missiles. You have to think of a tsunami not as a wave, but as a sudden, destructive rise in sea level coupled with an amazing amount of energy directed inland.
The only smart thing to do if you are near a coast and a tsunami alert is given is run like fuck for higher ground. Gaining twenty feet could save your life. Watch some of the videos from the 2004 Boxing Day Tsunami.. none of those people saw anything out of the ordinary until the surge was right on them.
It looks like we got off light here on the North American coast. Some damage to harbors and boats, a few morons who needed to be rescued from their own folly. We're still in the danger period, so I'm keeping my eyes open. Japan wasn't so lucky.
Remember people, ours is a big, dangerous planet and the universe has no mercy. Understand the risks!
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Date: 11 Mar 2011 21:32 (UTC)Compared with 200,000+ dead from the Indonesia quake, the estimates of 400 dead now and a possibility of 2000-3000 dead when it's all counted is still sad - but just so freaking amazing.
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Date: 11 Mar 2011 22:17 (UTC)It's not like a 5 foot wave. It's a a storm surge, only faster. The *base level* of the water is rising by several feet, and the existing waves wind up on top of that.
Sure, it's temporary. But during that "short" period (minutes, as opposed to the seconds of a normal wave) you've got a lot of water *and* time for it to do things.
So you get those deceptively slow flows going far inland.
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Date: 12 Mar 2011 10:21 (UTC)