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Saturday, November 06, 2010

Iceland Lake Disappearing Into New Crack in Earth







Bijal P. Trivedi
for National Geographic Today
October 1, 2001
Icelanders are accustomed to their land being stretched, split, and torn by violent earthquakes and haphazardly rebuilt by exploding volcanoes. But everyone was surprised when a large lake began to disappear into a long fissure created by one of last summer's earthquakes.

The draining lake is an oddity even by Icelandic standards, and has lured hordes of curious onlookers to it barren shores.

"If you put your ear to the ground, you can hear the lake draining," said geologist Amy Clifton of the Nordic Volcanological Institute in Reykjavik, Iceland. "It sounds like water going down the sink."
Last year, during a leisurely Sunday drive, a geologist noticed a large gash in the landscape about 20 kilometers (13 miles) from Reykjavik and reported it to Clifton. When she arrived she found a fissure—about a foot wide and 400 meters (1,280 feet) long—that led directly into Lake Kleifarvatn and disappeared beneath the water.
Lake Kleifarvatn, which measured about six kilometers (3.7 miles) long and 2.3 kilometers (1.4 miles) wide last year, has shrunk dramatically. Now it is only 3.5 kilometers long and roughly 1.8 kilometers wide, said Clifton.
Kleifarvatn is draining at about one centimeter (one-third of an inch) a day, according to Clifton. "You can almost see the lake level drop," she said.
Summerhouses that were once mere steps from waterfront are now more than a kilometer away from the water's edge. The placid waters have dropped more than four meters in the last year. In their place is a barren lake bed speckled with sulphur-rimmed thermal springs that spit boiling water and mud.
Clifton spends much of her time mapping and measuring "rips, gashes, and holes" in the Icelandic landscape. Describing herself as a "walking pencil," because her treks are all mapped by global positioning system (GPS) technology, she investigates open cracks, torn vegetation, rock falls, sinkholes, and other disturbances and tries to determine what caused them.
But what phenomenon created the large fissure at Lake Kleifarvatn is an enigma. "I couldn't find an earthquake in our database that was big enough to cause such a huge rupture in the surface," said Clifton.
She and some of her colleagues think a "quiet earthquake" may be responsible. Explaining such a scenario, Clifton said the water may have "lubricated the fault lines, allowing them to slide quietly and slowly, preventing the shock waves that would normally accompany an earthquake."
The earthquake thought to be responsible for the fissure at Lake Kleifarvatn occurred last year on June 17, about 80 kilometers (49 miles) east in the South Icelandic seismic zone. "No one ever expected earthquakes in this region to affect the surface in the Reykjanes Peninsula, where Lake Kleifarvatn is located," said Clifton.
Clifton hopes to eventually understand the relationship between the movement of faults deep within Earth and their surface effects in the region. Such knowledge is important for mapping areas that may be subject to future hazards, especially in regions where the population is growing.
While the Lake's dramatic disappearance is, for Clifton, "alarming, interesting, and unusual," she and her colleagues assume the waters will return. The last time a similar event happened was in 1912, after a magnitude 7 earthquake, and it took about three decades for the water level to normalize, she said.
Iceland experiences violent geological events because it sits at the Mid-Atlantic ridge—the boundary of the North American and European continental plates. The North American plate is shifting westward and the European plate is moving eastward. In the middle is a "hot spot," which spews the magma that has created the island of Iceland. Iceland grows by two centimeters (three-fourths of an inch) every year because of stretching and building caused by the combination of plate movements and volcanic activity.  
Clifton said: "Iceland is a natural laboratory for studying this stretching and understanding the time scale on which these events occur.


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