Tuesday thereafter the Chaiten volcano spewed lava and blasted ash more than 12 miles (20 km) into the sky, prompting a total evacuation of the provincial capital and other settlements. Wind-blown ash travelled hundreds of kilometres as far as Argentina's Chubut province, where town authorities issued health emergencies, closing down schools, airports and main roads, and distributing drinking water to some areas.
President Michelle Bachelet of Chile interrupted a speech to announce that "the volcano is exploding so a total evacuation of the town of Chaiten has been ordered." Later in the day she visited the area.
Rains following the eruption have carpeted surrounding areas in ash and mud. Hardest hit is Chaiten, a small provincial capital of wooden houses and cobblestone streets just 10 km (6 miles) from the volcano in southern Chile.
"There's no historical record on this volcano, so we have no way of knowing if the ash emissions will continue for weeks or even months," Interior Minister Edmundo Perez Yoma told reporters a day after the Chaiten volcano blew its top.
Chile is one of the most volcanically active regions in the world. It sits on the edge of the South American tectonic plate at a point where it forces the neighbouring Nazca plate, which holds the Pacific Ocean basin, into the earth’s mantle. This creates a weak point in the crust, allowing magma to force its way up. 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.
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.
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.
Charles Stern, a volcanologist at the University of Colorado-Boulder who studied Chaiten, said the nearby town could end up buried, much like the Roman city of Pompeii following Mount Vesuvius' eruption in 79 A.D. Volcanic material from Chaiten's last eruption measured up to 5 feet.
So far, Chaiten has emitted only a few thousand tons of sulphur dioxide, "which is very small," said Simon Carn, a University of Maryland-Baltimore volcanologist who uses satellites to measure volcanic gases.
“In general, a volcano must spew at least 1 million tons of sulphur dioxide into the stratosphere to have a global effect on climate,” said Alan Robock, a Rutgers University professor. After eruptions of unusual size, sulphur dioxide, converted into sulphuric acid, can form a thin white cloud in the atmosphere that reflects sunlight away from Earth.
But Robock said this volcano is so close to the South Pole that any cooling would likely be limited to the Southern Hemisphere.
if not stated otherwise, photographs with the courtesy of Reuters