DEADLY QUAKES INSIDE CONTINENTAL PLATES

According to researchers, the main reason for high death tolls within continental interiors is because inland quake zones are poorly mapped.

Our perception of seismic risk is skewed into thinking earthquakes at plate boundaries are more deadly. We're wrong.

Knowledge of seismic risk is badly skewed in favor of earthquakes that occur on plate boundaries, such as the March 11 temblor that hit northeast Japan, rather than those that strike deep inland, a pair of scientists said on Sunday.

In commentary appearing in the journal Nature Geoscience, Philip England of Oxford University and James Jackson of Cambridge University say that in seismic terms, the 9.0-magnitude Sendai quake was "a remarkable story of resilience."

Good civic training and building construction meant that the death rate was "impressively low," they said. Around 25,000 people died, or 0.4 percent of those exposed to the event, and most of these died from the tsunami that followed.

THE GIST

·     Earthquake preparedness is high around seismically active tectonic plate boundaries, often saving many lives and structures.

·   Quake death rates within continental interiors are higher than that of continental plate boundaries.

·   Their faults are often very complex and slow-moving, sometimes taking thousands of years to rupture.

The March 11 event occurred on a plate boundary, where the jigsaw of plates that float on Earth's crust jostle and grind and slide under each other.

England and Jackson say plate boundaries are relatively well-studied, but a far greater threat lurks in continental inland areas.

"Death rates in earthquakes within continental interiors have often exceeded five percent and can be as high as 30 percent," they warn.

According to their count, over the past 120 years, there have been around 130 quakes around the world where a thousand people or more have died.

Of these, about 100 have occurred in continental interiors, causing 1.4 million deaths, whereas earthquakes at plate boundaries have inflicted 800,000 deaths, roughly half of them by tsunamis.

Among the inland killers were those in Bam, Iran, which cost 30,000 lives in 2003; in Muzzafarabad, Pakistan, which led to 75,000 deaths in 2005; and the 2008 Wenchuan quake in China in 2008 in which 70,000 died.

The main reason for these high tolls is because inland quake zones are poorly mapped, the commentary says.

Their faults are often very complex and slow-moving, sometimes taking hundreds or even thousands of years to build up tension to the point where they rupture.

Jackson and England call for the study of inland faults to be given the same priority as boundary faults, starting with the 10 million square kilometers (3.86 million sq. miles) of the Alpine-Himalayan belt, which stretches from Italy, Greece and Turkey, across the Middle East, Iran and central Asia, to China.

"The severity of this threat is increasing rapidly as millions of people every year migrate into mega-cities in vulnerable locations, many of which were devastated by earthquakes in the past, when their populations were much smaller."

Source: Discovery News

ICELAND VOLCANO ERUPTS

Satellite image of Grimsvotn erupting in 2004.

The Grimsvoetn volcano under Iceland's largest glacier began erupting Saturday, the Icelandic Meteorological Office said, reporting a tall plume of smoke rising from the crater.

"An eruption at Grimsvoetn has started and there's an airplane on its way there now to investigate further," Haraldur Eirkisson of the office told AFP.

"There was a cloud rising up from Grimsvoetn around 1900 GMT and at just before 2000 GMT it had reached an altitude of 11 kilometers (6.8 miles)," he added.

Another meteorologist at the same office, Fridjon Magnusson, told AFP less than two hours later that the column of smoke had swelled to reach an altitude of 20 kilometers.

Grimsvoetn is Iceland's most active volcano, having erupted nine times between 1922 and 2004. It lies beneath the Vatnajoekull glacier in the southeast of the North Atlantic island nation.

The eruption in April last year of Iceland's Eyjafjoell volcano, southwest of Grimsvoetn, shut down large swathes of European airspace for almost a month amid fears the volcanic ash could wreak havoc on aircraft engines.

The Gist

·    Grimsvoetn volcano, located beneath Iceland's Vatnajoekull glacier, last erupted      in 2004.

·       Last year, Iceland's Eyjafjoell volcano, southwest of Grimsvoetn, shut down large swathes of European airspace for almost a month.

·    For now, it is not known if Grimsvoetn will produce the troublesome fine ash   Eyjafjoell generated.

No two volcanic eruptions are the same, and it remained unclear late Saturday if the new eruption threatened to emit a similar kind of ash -- fine, with very sharp particles -- like the massive plume that burst from Eyjafjoell.

"The eruption has not yet spread very far, and is still looming over the Vatnajoekull glacier," Magnusson pointed out.

"These are just the first few hours of the eruption. We can't say yet whether this will have an effect on air traffic like Eyjafjoell," he added.

The problem with last year's eruption, which caused the planet's biggest air space shutdown since World War II, was according to the researchers that it happened under a glacier, bursting through 200-300 meters of ice.

It was the "interaction between the cold water and the hot magma that made the particles really tiny," and therefore especially dangerous to aircraft, Susan Stipp, a professor at the Nano-Science Centre at the University of Copenhagen, told AFP late last month.

"The (ash) particles were small so they went high and far. They were sharp, so they were a danger to airplane windows. It's like sand-blasting the airplane. And they were small and could melt at temperatures common in jet engines ... and could cause failure," she told AFP.

While Saturday's eruption had sent smoke high in the sky, Magnusson pointed out that there so far was only "heavy ash at the bottom of the bloom (that) has not reached high heights."

Bjarni Steinthorsson, a farmer who lives near the Vatnajoekull glacier, meanwhile told the Morgunbladid daily's website small amounts of ash had begun falling in the area and "the snow is getting darker."

He said that he expected more ash to fall overnight, although what happened would depend on the direction of the winds, which were currently almost still at the eruption site.

Iceland's State Road Authority meanwhile announced late Saturday it had temporarily closed a road near the glacier that is part of the national highway system.

Grimsvoetn is also located under a glacier, in an enormous, eight-kilometer (five-mile) diameter caldera -- a collapsed volcanic crater -- near the center of the Vatnajoekull icefield.

When it last erupted in November 2004, volcanic ash fell as far away as mainland Europe and caused minor disruptions in flights to and from Iceland.

Geologists had worried late last year the volcano was about to blow when they noticed a large river run caused by rapidly melting glacier ice.

Eruptions at Grimsvoetn traditionally result in massive flooding, although this has little impact since the surrounding areas are uninhabited.

Source: Discovery News

Facts about Volcanoes

Volcanoes are awesome manifestations of the fiery power contained deep within the Earth. These formations are essentially vents on the Earth's surface where molten rock, debris, and gases from the planet's interior are emitted.

When thick magma and large amounts of gas build up under the surface, eruptions can be explosive, expelling lava, rocks and ash into the air. Less gas and more viscous magma usually mean a less dramatic eruption, often causing streams of lava to ooze from the vent.

The mountain-like mounds that we associate with volcanoes are what remain after the material spewed during eruptions has collected and hardened around the vent. This can happen over a period of weeks or many millions of years.

A large eruption can be extremely dangerous for people living near a volcano. Flows of searing lava, which can reach 2,000 degrees Fahrenheit (1,250 degrees Celsius) or more, can be released, burning everything in its path, including whole towns. Boulders of hardening lava can rain down on villages. Mud flows from rapidly melting snow can strip mountains and valleys bare and bury towns. Ash and toxic gases can cause lung damage and other problems, particularly for infants and the elderly. Scientists estimate that more than 260,000 people have died in the past 300 years from volcanic eruptions and their aftermath.

Volcanoes tend to exist along the edges between tectonic plates, massive rock slabs that make up Earth's surface. About 90 percent of all volcanoes exist within the Ring of Fire along the edges of the Pacific Ocean.

About 1,900 volcanoes on Earth are considered active, meaning they show some level of activity and are likely to explode again. Many other volcanoes are dormant, showing no current signs of exploding but likely to become active at some point in the future. Others are considered extinct.

Source: National Geographic