A towering cloud of hot ash, gas and molten rock spewed miles into the air by a volcano in southern Chile has partially collapsed, raising fears it could smother surrounding villages, an expert said on Tuesday. Luis Lara, a scientist with the government's geology and mining agency, said the column of ash, which had soared as high as 20 miles (30 km), was now about 4.5 miles (7 km). The column of debris, kept aloft by the pressure of constant eruptions, could collapse entirely, smothering the ghost town of Chaiten 6 miles (10 km) away with hot gas, ash and molten rocks.