Correction to This Article
The article incorrectly described Iceland as about 100 miles long and 60 miles wide. Iceland is, at its most distant points, 304 miles wide and 194 miles from north to south. The total area is about 39,769 square miles, making the country slightly smaller than Kentucky.

Iceland is among the world's most volcanically active places

The Eyjafjallajokull volcano in southern Iceland has erupted twice in less than a month, raising concerns that it could trigger a larger and more dangerous eruption at a volatile volcano nearby.
By Marc Kaufman
Washington Post Staff Writer
Saturday, April 17, 2010

The volcano erupting from beneath Iceland's Eyjafjallajokull glacier and causing airport closures across northern Europe is a typical example of the kind of shield volcanoes that formed the island and still erupt on a regular basis.

The Icelandic eruptions are much less forceful than the ones that occur regularly in Alaska and elsewhere around the Pacific Ring of Fire, but they have been active for eons and are enormous when their full size is taken into account -- from the bottom of the ocean to the top of the volcano.

"Because of where it sits, Iceland is one of the most volcanically active places in the world," said Chris Waythomas, scientist in charge of the Alaska Volcano Observatory, an arm of the U.S. Geological Survey, in conjunction with the state and the University of Alaska. "It was bad luck that the wind took the ash where it did, but this kind of thing happens all the time."

Iceland has 35 active volcanoes on or around the island, which is about the size of the state of Kentucky. This volcano's last eruption was in 1821 and lasted for 13 months.

The volcanic activity comes from two sources -- Iceland is in a geological hot spot, where the molten magma of the Earth mantle is closer to the surface than in most places. It is also in the mid-Atlantic rift zone, with its long ridges and valleys at the ocean floor, where two of the globe's huge continental plates are regularly pulling apart. This also causes a weakening of the crust, which allows undersea volcanoes to erupt and magma to pour out.

The airline cancellations across Europe are the result of abrasive ash that the volcano sends into the sky. Unlike ash from burning leaves or other organic material, this ash is a combination of small, pulverized rock and glass created in the cauldron of hot magma. The ash can not only clog engines but can scratch and corrode glass and metal on airplanes.

The result, Waythomas said, is that whenever volcanic ash is in the sky, airplanes are obliged to keep away. "Pilots are under orders to ground their aircraft when they pass through an ash cloud," he said. "That makes it pretty obvious that they don't want to be near an ash cloud to begin with."

The ash coming from Iceland is quite fine, and experts say it might not even be detectable if it lands in Europe. In contrast, the ash in Alaska is so thick that residents have learned to never use their windshield wipers to clean their car windows after an eruption. If they did, the ash -- rock and glass -- would quickly make the window badly scratched and useless.

The Alaska Volcano Observatory monitors more volcanoes than any center in the world and is frequently putting together the information that results in airport closures across Alaska and elsewhere. Identifying and following the ash clouds might seem like a straightforward task, but Waythomas said it gets quite difficult as the cloud gets thinner while remaining hazardous.

Volcanoes come in several varieties: the shield type of Iceland and Hawaii; the stratovolcanoes, or stratocone volcanoes, that grow dramatic and tall, such as Mount Fuji and Mount St. Helens; and cinder cone volcanoes that are smaller but especially steep above their vents. The shield volcanoes produce lava (the term for magma once it leaves the volcano) that is watery and thin and consequently spreads out for miles. Stratovolcanoes, which tend to be more explosive, send out thicker lava and less of it. This has the effect of keeping the lava close to the volcano and building it into a taller, sleeker mountain. Cinder volcanoes, which can grow quickly and often form nearby larger shield or stratovolcanoes, tend to be the least explosive and dramatic.

The magma that erupts from volcanoes is molten rock, mixed with gases and water, that comes from the Earth's outer core. It very gradually makes its way up through the deep mantle of the planet to the crust, where it sits until it is under pressure great enough to push through weak spots.

Volcanoes play an essential role in cycling elements from deep underground to the Earth's surface, and many forms of lava over time turn into rich farmland. But large eruptions can also bring about periods of global cooling -- as seen after the 1991 eruption of Mount Pinatubo in the Philippines and in the 1783 eruption of the Laki volcano in Iceland, which caused an abnormally cold winter across Europe. The climate change is less a function of the ash than of the sulfur dioxide that is released during an eruption.

Shield volcanoes got their name in Iceland because they look like the broad shields that warriors used centuries ago. The tallest volcano in the solar system, Olympus Mons on Mars, is a shield volcano about 16 miles high and 400 miles across.

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