Severe earthquakes in Haiti, Chile and now Japan have experts around the world asking whether the world's tectonic plates are becoming more active — and what could be causing it.
Some scientists theorize that the sudden melting of glaciers due to man-made climate change is lightening the load on the Earth's surface, allowing its mantle to rebound upwards and causing plates to become unstuck.
These scientists point to the historical increase in volcanic and earthquake activity that occurred about 12,000 years ago when the glaciers that covered most of Canada in an ice sheet several kilometres thick suddenly melted.
The result was that most of Canada's crust lifted — and is still rising.
Scientists have discovered that the accelerated melting of the Greenland ice sheet over the last 10 years already is lifting the southeastern part of that island several millimetres every year.
The surface of the Earth is elastic. A heavy load such as a glacier will cause it to sink, pushing aside the liquid rock underneath.
The Greenland glacier is about three kilometres at its thickest and it is believed that its weight has depressed sections of the land under the glacier about one kilometre. In fact, the weight of the glacier is so great that significant portions of Greenland have been pushed well below sea level.
"There is certainly some literature that talks about the increased occurrence of volcanic eruptions and the removing of load from the crust by deglaciation," said Martin Sharp, a glaciologist at the University of Alberta. "It changes the stress load in the crust and maybe it opens up routes for lava to come to the surface.
"It is conceivable that there would be some increase in earthquake activity during periods of rapid changes on the Earth's crust."
Other scientists, however, believe that tectonic movements similar to the one that caused the Japanese quake are too deep in the Earth to be affected by the pressure releases caused by glacier melt.
These scientists theorize, however, that glacier melts could cause shallower quakes.
Andrew Hynes, a tectonics expert at McGill University, said the issue is not so much the load shift on the Earth's crust, but rather the increased fluid pressure in the fault that lubricates the rock, allowing the plate to slide.
"All earthquakes, except those produced by volcanic activity, are essentially the unsticking of faults," he said.
In other words, if you pump fluid into a fault, it can reduce the friction and allow the rock to slide.
Could the stress transfers and the added melt from glaciers inject more fluid into the rocks, creating earthquakes?
"It would only apply to earthquakes that are at shallow depths," he said. "But I wouldn't push it any further than that."
He added, however, that the decompression from melting glaciers could cause an increase in volcanic activity by releasing the liquid rock and its explosive potential.
At the same time, the number and severity of earthquakes appear to have increased over the last thirty years in tandem with accelerating glacial melt.
Some experts claim that jump can be explained by the increased number of seismograph stations — more than 8,000 now, up from 350 in 1931 — allowing scientists to pinpoint earthquakes that would otherwise have been missed.
But this does not explain the recent increase in major earthquakes, which are defined as above 6 on the Richter magnitude scale. Japan's earthquake was a 9.
Scientists have been tracking these powerful quakes for well over a century and it's unlikely that they have missed any during at least the last 60 years.
According to data from the U.S. Geological Survey there were 1,085 major earthquakes in the 1980s. This increased in the 1990s by about 50 per cent to 1,492 and to 1,611 from 2000 to 2009. Last year, and up to and including the Japanese quake, there were 247 major earthquakes.
Some scientists theorize that the sudden melting of glaciers due to man-made climate change is lightening the load on the Earth's surface, allowing its mantle to rebound upwards and causing plates to become unstuck.
These scientists point to the historical increase in volcanic and earthquake activity that occurred about 12,000 years ago when the glaciers that covered most of Canada in an ice sheet several kilometres thick suddenly melted.
The result was that most of Canada's crust lifted — and is still rising.
Scientists have discovered that the accelerated melting of the Greenland ice sheet over the last 10 years already is lifting the southeastern part of that island several millimetres every year.
The surface of the Earth is elastic. A heavy load such as a glacier will cause it to sink, pushing aside the liquid rock underneath.
The Greenland glacier is about three kilometres at its thickest and it is believed that its weight has depressed sections of the land under the glacier about one kilometre. In fact, the weight of the glacier is so great that significant portions of Greenland have been pushed well below sea level.
"There is certainly some literature that talks about the increased occurrence of volcanic eruptions and the removing of load from the crust by deglaciation," said Martin Sharp, a glaciologist at the University of Alberta. "It changes the stress load in the crust and maybe it opens up routes for lava to come to the surface.
"It is conceivable that there would be some increase in earthquake activity during periods of rapid changes on the Earth's crust."
Other scientists, however, believe that tectonic movements similar to the one that caused the Japanese quake are too deep in the Earth to be affected by the pressure releases caused by glacier melt.
These scientists theorize, however, that glacier melts could cause shallower quakes.
Andrew Hynes, a tectonics expert at McGill University, said the issue is not so much the load shift on the Earth's crust, but rather the increased fluid pressure in the fault that lubricates the rock, allowing the plate to slide.
"All earthquakes, except those produced by volcanic activity, are essentially the unsticking of faults," he said.
In other words, if you pump fluid into a fault, it can reduce the friction and allow the rock to slide.
Could the stress transfers and the added melt from glaciers inject more fluid into the rocks, creating earthquakes?
"It would only apply to earthquakes that are at shallow depths," he said. "But I wouldn't push it any further than that."
He added, however, that the decompression from melting glaciers could cause an increase in volcanic activity by releasing the liquid rock and its explosive potential.
At the same time, the number and severity of earthquakes appear to have increased over the last thirty years in tandem with accelerating glacial melt.
Some experts claim that jump can be explained by the increased number of seismograph stations — more than 8,000 now, up from 350 in 1931 — allowing scientists to pinpoint earthquakes that would otherwise have been missed.
But this does not explain the recent increase in major earthquakes, which are defined as above 6 on the Richter magnitude scale. Japan's earthquake was a 9.
Scientists have been tracking these powerful quakes for well over a century and it's unlikely that they have missed any during at least the last 60 years.
According to data from the U.S. Geological Survey there were 1,085 major earthquakes in the 1980s. This increased in the 1990s by about 50 per cent to 1,492 and to 1,611 from 2000 to 2009. Last year, and up to and including the Japanese quake, there were 247 major earthquakes.
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