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IN FRATERNAM MEAM
Sunday, March 27, 2005
TSUNAMI TRIGGERS
Earthquakes
The most destructive and common tsunamis are spawned by earthquakes. To Deform the sea bottom and displace enough water to propel wave pulses for a thousand miles or more, a quake has to be colossal, at least a magnitude of 7.5. Typically, s tsunamiquake occurs at a thrust fault, where an ocean plate dives under a continental plate, dragging it down until the fault snaps, causing an earthquake that lifts the seafloor.

WHERE NEXT?
Russia's Kamchatka Peninsula and the coastline border of Peru and Chile are among the most "Tsunamigenic" in the world.

Volcanoes
A classic aboveground eruption is just one of the ways a volcano can disturb the ocean and generate a tsunami. Waves can also be triggered by submarine events-- eruptions, cascades of ash, or the collapse of a volcanic explosion of Krakatau and the collapse of its caldera stirred up 130 foot high waves and killed some 36,000 people.

WHERE NEXT?
The submarine Loihi Volcano southeast of the Big Island of Hawaii and the Izu village arc off the east coast of Japan are being closely watched.


Landslides
The volcanic displacement of water from landslides, usually set off by earthquakes, and from rock and icefalls can create powerful local tsunamis. The highest recorded swept Lituya Bay, Alaska, in 1958, when a quake triggered rockfall threw up a 1,720 foot wave--267 feet higher than the Empire State Vuilding.

WHERE NEXT?
Continental shelves where sediments collect and the unstable flanks of volcanoes are landslide prone. Scientist are keeping an eye of the west coast of the U.S. off Santa Barbara, California and the east coast of southern Virginia and North Carolina.


Asteroids
A Hollywood style, doomsday tsunamic washing over New York City and pouring inlands as far as the Applachian mOuntains could happen if an asteroid of three to four miles in diameter hurtle into the middle of the Atlantic Ocean. While no known asteroid or comet has hit earth during recorded history, 35 millions years ago one blasted a 53 mile wide crater under what is now the southern end of the Chesapeake Bay. The resulting waves -- possibly thousands of feet high-- roared inland for hundred of miles.

WHERE NEXT?
With luck, some other planet.

(abstracted from GEOGRAPAHICA/find more tsunami facts and links to the latest research in our Online Extra at national geographic.com/magazine/0504
posted by infraternam meam @ 11:37 PM  
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Name: infraternam meam
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About Me: I am now at the prime of my life and have been married for the past 25 years. Sickly at times, but wants to see the elixir vita, so that I will be able to see my grandchildren from my two boys.
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