posted 03-25-2005 09:50            

Tsunami's can also be triggered by submarine events--eruptions, cascades of ash, or the collapse of a volcanic flank.

Where next: The submarine Loihi Volcano southeast of the Big island is being closely watched.

posted 03-25-2005 11:03            

Tina

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You can see my timeshare photos here:

posted 03-25-2005 12:35               

From Roadside Geology of Hawaii by Hazlett and Hyndman (a book that any serious Hawaii traveler should own), pp. 39-41:

quote:

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Drowned Valleys and Tsunami

Streams carve valleys into the island as it sinks. Seawater floods the lower valley floor, and streams, landslides, and lave flows fill it, making a broad flatland framed between high canyon walls. You can mentally reconstruct the valley's orginal depth by projecting the slopes of the valley walls downward to where they meet hundreds of feet below the surface. In most cases, the sediment fill turns out to be hundreds of feet deep.
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The sinking stream valleys of Hawai`i are potentially treacherous places to live because of the funneling effect they have on giant sea waves called tsunami. Most tsunami start when sudden movement on a fault shifts a large area of the ocean floor vertically, to the accompaniment of an earthquake.
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Although earthquakes account for most of the tsunami that strike Hawai`i, the biggest waves arise from giant landslides suddenly dumping large chunks of a volcano into the ocean. Although none have been in historic time, geologic evidence gives some idea of their size: Geologists have discovered loose blocks of reef limestone 1,070 feet up the slopes of Lāna`i. These blocks were torn loose by a tsunami coming from the south about 100,000 to 105,000 years ago. Lāna`i stood higher then than it does today, so the wave may have risen even higher. The same tsunami probably stripped all of the soil off the island of Kaho`olawe below a present elevation of 800 feet.

The effects of another monster tsunami in Hawaiian waters would be catastrophic beyond imagining, considering that the tsunami that wiped out downtown Hilo in 1946 was only about 20 feet high. It seems likely that most of the people who live in the coastal lowlands would drown - more than 95 percent of the population of the state. Such a wave would come with little or no warning because it would originate in local waters. Fortunately, monster tsunamis are so infrequent that there is no practical reason to worry about them.

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Most of the spectacular sea cliffs in Hawaii - such as the Na Pali coast, the NE shore of the Big Island, the north side of Molokai - were formed by massive landslides when up to half of a volcano suddenly breaks loose and slides into the ocean. All of the Hawaiian Island are geologically unstable - the bases of the volcanoes are unable to support their weights.

posted 03-25-2005 20:16            

Hawaii is probably the most tsunami instrumented area in the world--don't let me scare you away from the Islands.

posted 03-26-2005 01:28            

Recently there was one that hit Oahu (about a year or two ago), but it was only about an inch high and did no damage, obviously.

posted 03-26-2005 15:01               

These rifts are common to almost all Hawaiian volcanoes. When there is a massive, catastrophic landslide, the slide usually occurs along rifts such as this.

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Steve Nelson