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Archive for the ‘geology’ Category

Major Earthquakes Increase 47 % in 3 Decades

Posted by feww on December 13, 2008

Worldwide Earthquakes [Magnitude 6 to 9.9] have increased by 47 percent in under 3 decades

A total of  1,085 earthquakes measuring magnitude 6 or greater occurred between 1980 to 1989, averaging 109 per year over the decade. In the 1990s the decadal total increased to 1,492 averaging at 149 major earthquake  per year over the period.

Since January 1, 2000 [ see table below for the date and time] a total of 1,438 major earthquakes have so far occurred worldwide raising the annual total over the last 9 years to 160 with more than 12 and a half months to go to the decade’s end.

The increase from 109 to 160 major earthquakes per year in the 1980 to 2008 period translates to a rise  of 47 percent in just under three decades.

major-worldwide-earthquakes
Major Worldwide Earthquakes [Magnitude 6 to 9.9] – 1980 to 2008 – Source of data: USGS.

Other Data

With an estimated total death toll of 88,072 [as of Dec 3, 2008,] this year has seen the second worst number of human casualties caused by earthquakes since 1980. The largest earthquake/ tsunami related casualties for the 29-year period occurred in 2004 with an estimated total of 228,802 deaths.  [The stats are based on USGS data.

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Posted in Earthquake Information, geology, Seismology, Subduction, Tectonic Boundaries | Tagged: , , , , | 5 Comments »

Chaitén’s Fury Ending?

Posted by feww on May 31, 2008

Chaitén Update # 3

Is Weary Chaitén Ready to Rest?

Chaitén continues to erupt, although a decline in the height of eruption column in the last two days has been reported. A decline also in its seismic activity is reducing the probability of larger explosive eruptions, though they are not entirely ruled out.

Air Lines Resume Flights Over Central and Southern Chile

Airlines resumed flights to most of southern Chile airports on Thursday after they were briefly suspended because of the high concentration of ash in the atmosphere.

Flights to Puerto Montt and Temuco remain on stand by until further notice; however, flights to Punta Arenas and Balmaceda have resumed.

Chaitén volcano started erupting May 2, after at least 9,000 years of dormancy.

JNM-Chaiten_5-26-08_M
Typical eruption column of Chaiten Volcano, Chile, on May 26, 2008, between stronger explosive activity. The circular caldera rim is 3 km (1.9 miles) in diameter, which was formed about 9,400 years ago. A lava dome that erupted sometime later is the knobby feature between the billowing ash and rim on the left. A new lava dome is growing in the caldera but it is out of view behind eruption column. U.S. Geological Survey photograph by J.N. Marso. Caption: Hawaiian Volcano Observatory.

Cerro Azul Volcano Erupts

Meanwhile the 1,700-meter high Cerro Azul volcano erupted on Thursday after 10 years of inactivity. Cerro Azul is located on Isabela, the largest of the Galapagos islands.


Cerro Azul volcano at the SW tip of Isabela Island. Photo by Tom Simkin (Smithsonian Institution). Image Maty be subject to copyright. See FEWW Fair Use Notice!

The Galápagos archipelago, a province of Ecuador, has a population of around 40,000 and is located the eastern Pacific Ocean at 525 nautical miles (972 km/604 miles) off the west coast of South America. The sparsely archipelago is home to “Galápagos,” the Spanish name for the Giant Land Tortoises that inhabit the islands.


Satellite photo of the Galápagos islands (names of the visible main islands are overlayed).

Unlike the 1998 Cerro Azul eruption in which several giant tortoise were destroyed by molten lava, despite a rescue operation by helicopters, it is thought that the current eruption poses no danger to the animals.

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Vanishing Lakes

Posted by feww on April 18, 2008

Source: Media Relations

Researchers from the Woods Hole Oceanographic Institution (WHOI) and the University of Washington (UW) have for the first time documented the sudden and complete drainage of a lake of meltwater from the top of the Greenland ice sheet to its base.

From those observations, scientists have uncovered a plumbing system for the ice sheet, where meltwater can penetrate thick, cold ice and accelerate some of the large-scale summer movements of the ice sheet.

According to research by glaciologists Sarah Das of WHOI and Ian Joughin of UW, the lubricating effect of the meltwater can accelerate ice flow 50- to 100 percent in some of the broad, slow-moving areas of the ice sheet.


WHOI glaciologist Sarah Das stands in front of a block of ice that was raised up 6 meters by the sudden drainage of a meltwater lake in Greenland. (Photo by Ian Joughin, UW Polar Science Center)” Image may be copyrighted. See FEWW Fair Use Notice!

“We found clear evidence that supraglacial lakes—the pools of meltwater that form on the surface in summer—can actually drive a crack through the ice sheet in a process called hydrofracture,” said Das, an assistant scientist in the WHOI Department of Geology and Geophysics. “If there is a crack or defect in the surface that is large enough, and a sufficient reservoir of water to keep that crack filled, it can create a conduit all the way down to the bed of the ice sheet.”

But the results from Das and Joughin also show that while surface melt plays a significant role in overall ice sheet dynamics, it has a more subdued influence on the fast-moving outlet glaciers (which discharge ice to the ocean) than has frequently been hypothesized. (To learn more about this result, read the corresponding news release from UW.)

The research by Das and Joughin was compiled into two complementary papers and published on April 17 in the online journal Science Express. The papers will be printed in Science magazine on May 9. Full press release Copyright ©2007 Woods Hole Oceanographic Institution, All Rights Reserved.

Posted in geology, Geophysics, glaciers, hydrofracture, Oceanography | Tagged: , , , , , , , , | 1 Comment »