Chile's Chaiten volcano, which erupted spectacularly last year, spewed a vast cloud of ash as well as gas and molten rock today in a partial collapse of its cone.
Television footage showed a cloud of ash billowing into the sky over the town of Chaiten, which lies about 10km from the crater.
Authorities evacuated 160 people from the area. Around 7,000 nearby residents were evacuated last year after the volcano, dormant for thousands of years, erupted. The government is planning to relocate the town.
Officials from Chile's national emergency office, Onemi, flew over the volcano and saw a kilometer-long crack in the cone of ash that has steadily grown in the crater, part of which has collapsed.
"Large quantities of gases and pyroclastic material were observed," Onemi said in a statement, adding that rains in the area combined with the ash could cause flooding in and around the town of Chaiten, located 1,220km south of the capital Santiago.
However, while there was a large volume of ash, there had been none of the earth tremors or groaning sounds that accompanied the initial eruption last year, it said.
"This is more proof of the imminent risk in the area. It is a time-bomb," said Deputy Interior Minister Patricio Rosende said.
The government insists on moving the entire town, but some residents are resisting the plan
"I looked up and saw a tremendous column (of ash), just like in the beginning, one-and-a-half kilometers high," Claudio Chelgui, a resident who decide to return to Chaiten despite government warnings, told local radio.
"I didn't see much because it was overcast, and there was this huge column and fierce sound."
Emergency officials are exasperated.
"We have repeatedly said that there is a red alert and that people should not be there, and if that had been respected, then police would not be evacuating people," an Onemi official said, asking not to be named.
He said the volcano has been in a permanent state of eruption since May last year, when a cloud of debris soared as high as 32km into the air. The cloud was kept aloft for weeks by the pressure of constant eruptions, covering towns in neighboring Argentina with volcanic ash.
Chile's chain of volcanoes, the second-largest in the world after Indonesia, includes some 2,000, and 500 of those are potentially active.
Reuters