While the eruption of the Grímsvötn volcano in Iceland is the most powerful in decades, it isn't likely to cause the same kinds of disruption as Eyjafjallajökull did last year.

When Eyjafjallajökull erupted last March, the ash plume spread over much of Europe and resulted in huge disruptions to air travel, costing billions of dollars and stranding thousands of travelers. Aviation authorities will ground flights when the ash concentrations rise above a certain level because the ash can abrade engines and damage them, much like sandpaper. Grímsvötn's eruption, geologists say, differs from Eyjafjallajökull's in several ways.

First is the kind of ash clouds that the two mountains produce. The ash from Eyjafjallajökull was made up of smaller particles than that from Grímsvötn. According to a new study by the Institute of Earth Sciences at the University of Iceland, much of the ash -- about 20 percent -- from Eyjafjallajökull was made up of particles less than 10 microns across. That's small enough to get lofted much higher into the atmosphere and travel a much greater distance. The ash from Grímsvötn is made up of larger pieces, which means it falls out of the air more quickly, though it can still travel quite far.

The ash from Eyjafjallajökull was also more angular, like shards of glass. This is partly due to the kind of magma that produced it. The magma from Eyjafjallajökull had much more silica. It was 63 percent silica versus 50 percent in Grímsvötn. That made the magma stickier -- giving it a more clay-like consistency. It also meant that when the magma hit the ice sitting on top of the volcano it exploded with much more power and violence, resulting in smaller and sharper ash particles.

A third factor is weather. John Stevenson, a research fellow at the School of Geosciences in Edinburgh, notes on his blog that there was a high pressure system sitting over Europe and the North Atlantic when Eyjafjallajökull erupted, which brought the ash right over Europe. This time most of the wind is pushing the plume out over the Arctic.

Stevenson notes that Grímsvötn is actually a bigger eruption, if it is measured by the sheer volume of rock the volcano has spewed out. When it erupted on Saturday the ash plume reached a height of 20,000 meters (65,000 feet). Eyjafjallajökull's plume only got to a height of about 9,000 meters (29,500 feet). Eyjafjallajökull belched out some 10,000 cubic meters of material per second, while Grímsvötn could be discharging 1,000 times that.

The combination of a different type of ash, better preparedness on the part of European aviation authorities, and different weather conditions will make this volcanic eruption less of a problem for air travelers, at least so far (though it has already put a crimp in President Barack Obama's flight plans).

The British Met Office is reporting that the ash plume has reached the British Isles and eastern Greenland, and part of it has moved into northwestern Russia. While some flights to Scotland and England were grounded, airlines are flying fairly normally into the rest of Europe.

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