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Tsunami

The good thing about living near the geographic center of the continent (Belle Fourche, SD) is that we don’t have to worry much about Tsunami waves.  This does not however diminish the significance of the recent disaster in the Indian Ocean.  When I first heard about the event, national news media were reporting a magnitude 8.9 quake (ended up with a 9.0 rating) with hundreds dead.  My immediate response was, “I bet at least 30,000 died because of the wave alone”.  I underestimated the disaster by a factor of 10!  As an earth scientist who has some knowledge of such events, I find myself annoyed when I listen to the misinformation being broadcast by the national news media. The Examiner will get it right.

There is no question that this December 26th earthquake generated phenomena was one of the great catastrophic events of our lifetime.  With over 200,000 dead reported to date, it ranks up with the top three or 4 naturally caused major human losses of life since the 15th century AD.  This Tsunami was in fact caused by a great magnitude 9 earthquake.  Great earthquakes have killed many over the years.  In 1886, over 36000 people were killed by the explosion of Krakatoa volcano in the same area by a combination of earthquake shaking and Tsunami waves. Interestingly, also on December 26th but in 2003, a big quake in Bam, Iran, killed 40,000 people or half it’s population.  In 1976, it is reported that 250,000 people were killed by a quake in Tangshan China. Again in China, in the year 1556, over 830,000 were killed by a trembler. By contrast, the 1906 San Francisco quake caused an estimated 3000 deaths. These reports are of course from all earthquake related causes with Tsunami being a factor with only Krakatoa.

Here are some facts about this recent event contrary to media reports I personally heard. While it is true that over the open ocean, Tsunami waves can travel at the speed of a passenger jet liner. They do not, as reported, slam into the coastline at 500 miles per hour.  This kind of rogue wave is generated because during an particular kind of earthquake generated ground movement, and because of this movenet, huge amounts of water are displaced.  If the sea floor moves upward (for example) by 20 yards, the entire water column is pushed up causing of dome of water that will start flowing in all directions.  This event will travel outward at the speed at which the ground movement occurred which is close to the velocity of seismic waves.  On the ocean surface this expresses itself as a low amplitude wave only a few feet high but with a wavelength of many miles but the wave extends all the way to the sea floor.  In the open ocean, you might not even notice such a wave pass under your boat but when the wave hits shallow water, the front of the wave slows way down and the back of the wave catches up.  This causes the water to pile up and raise to the great heights that we have seen on all these videos.  In fact the wave slams into the shore at about 30 miles per hour which is faster than a horse can run.

The damage and most of the loss of life is caused by the mixing action of the water which I compare to being stuck in a blender on puree. In some areas of Sumatra closer to the great quakes epicenter, the quake knocked down almost every house, only to have the town pureed and then wiped out to sea by the first advancing, then retreating wave. The initial wave front picked up all the debris capable of floating which beat and buffeted any body trying to swim in the morass.  Many women drowned because their long hair entangled in debris. Others were just crushed by the trees and building material mixed in with the water. Women and children died disproportionately because in this area of the world, the men are mostly fisherman, strong swimmers and were out in boats at the time. Women were also burdened trying to save their children.

While the media focus on the waves, the root cause was an earthquake.  There is no question that the United States government needs to improve the existing Pacific Basin Tsunami warning system.  Additionally, new systems need to be installed in the Caribbean and Atlantic Basins.  As I said before, it is good to live mid-continent.

Following are some other earthquake facts, courtesy of the U.S. Geological Survey and other sources:

• The earthquake the generated the Indian Ocean Tsunami had energy equivalent to 99,000,0000 tons of TNT.

• Across the world, approximately 80,000 earthquakes occur every month, which equates to 2,600 per day an or 2 per minute

• The largest recorded earthquake in the world was a magnitude 9.5 in Chile on May 22, 1960.

• The largest recorded earthquake in the United States was a magnitude 9.2 that struck Prince William Sound, Alaska, on Good Friday, March 28, 1964.

• From 1975 to 1995, there were only four states that did not have any earthquakes. They were Florida, Iowa, North Dakota and Wisconsin.

• Powder River County is at fairly low risk for earthquakes but there is a small probability that we could sustain a 6.5 magnitude quake.

• The worlds largest potentially active volcano (and earthquake producer) is located in northwestern Wyoming (Yellowstone). The last time it blew up, it covered Texas in nearly a foot of ash.
More on Yellowstone in a later column.

The best website I have found to date for the recent Tsunami is www.waveofdistruction.org

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