Volcano Watch 2008,

BOGOTA, Colombia (AP) — Colombia's Nevado del Huila volcano erupted in a shower of hot ash, prompting thousands of people to leave their homes on Tuesday.

Smoke rises from the Chaiten volcano, May 2, 2008. The volcano in southern Chile spewed ash before dawn on Friday, triggering tremors 12 miles away and prompting evacuations, officials said.

Source

The Chaiten volcano last erupted more than 9,000 years ago, throwing out millions of tons of material and creating a crater two miles wide.

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Experts believe that magma has been trickling through the crust into a chamber beneath Chaiten, increasing the pressure as more of the liquid rock and gas filled the void left by the last explosion.

This week’s eruption was caused by magma forcing its way up through the crust beneath the volcano.

Scientists in Chile are now frantically collecting data in an attempt to measure how much magma has built up under the volcano.

"This could be an isolated incident or the start of quite a long period of rumbling," said Prof Clive Oppenhiemer, a volcanologist at Cambridge University.

Chaiten is a caldera volcano, which can explode in a cataclysmic eruption, emptying the magma chamber and causing the dome and surrounding land to collapse into the void beneath.

PUERTO MONTT, Chile (AFP) — A volcano in southern Chile erupted with renewed vigor Tuesday, raining ash and lava over its surroundings and forcing a total evacuation in a 30-kilometer (19-mile) radius, the National Emergency Office said.

APRIL 2008 Yellowstone Seismicity Summary

During the month of April 2008, 70 earthquakes were located in the Yellowstone Region. The largest of these shocks was a magnitude 1.7 event on April 17, 2008 at 6:56 AM MST, located about 13 miles North Northwest of Pahaska Tepee, WY and 19 miles North East of Fishing Bridge, WY. This earthquake was not felt. There were no earthquake swarms. Earthquake activity in the Yellowstone region is at relatively low background levels.

Earthquake activity in the Yellowstone region is at normal background levels.

Ground Deformation Summary: Through April 2008, continuous GPS data show that most of the Yellowstone caldera continued moving upward at similar to slightly lower rates as the past year. The maximum measured ground uplift over the past 40 months is ~20 cm at the White Lake GPS station. An example can be found at: pboweb.unavco.org...

The general uplift of the Yellowstone caldera is scientifically interesting and will continue to be monitored closely by YVO staff.

An article on the current uplift episode at Yellowstone and discussion of long-term ground deformation at Yellowstone and elsewhere can be found at: volcanoes.usgs.gov...