Chile volcano blasts ash 20 miles high, forcing evacuations

Lava was rising within this crater but has not yet spilled over, said Luis Lara, another volcanologist with the government's Geology and Mining Service.

The few remaining residents of Chaiten were transferred to two navy ships Tuesday, a day after President Michelle Bachelet visited the town, pledging financial help for people whose homes were damaged or livestock died after foraging on ash-covered grass.

Experts said it is too early to say whether the volcano will affect the world's climate.

So far, Chaiten has emitted only a few thousand tons of sulfur dioxide, "which is very small," said Simon Carn, a University of Maryland-Baltimore Campus volcanologist who uses satellites to measure volcanic gases.

In general, a volcano must spew at least 1 million tons of sulfur dioxide into the stratosphere to have a global effect on climate, said Alan Robock, a Rutgers University professor who co-authored a book on the subject.

After eruptions of unusual size, sulfur dioxide, converted into sulfuric acid, can form a thin white cloud in the atmosphere that reflects sunlight away from Earth.

The Philippines' Mount Pinatubo produced a brief cooling of the climate after spewing 20 million tons of sulfur dioxide in 1991.

But Robock said this volcano is so close to the South Pole that any cooling would likely be limited to the Southern Hemisphere.

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Associated Press Science Writer Seth Borenstein in Washington, D.C., contributed to this report.