Puyehue Volcano Eruption, Andes, Chile

On May 24, 1960, 38 hours after the main shock of the 1960 Valdivia earthquake, the largest earthquake recorded in history, Cordón Caulle began a rhyodacitic fissure eruption. The earthquake had struck the whole of Chile between Talca (30°S) and Chiloé (43°S) and had an estimated moment magnitude of 9.5. Being located between two sparsely populated and by then isolated Andean valleys the eruption had few eyewitnesses and received little attention by local media due to the huge damages and losses caused by the main earthquake. The eruption was fed by a 5.5 kilometres (3 mi) long and north west-west (N135°) trending fissure along which 21 individual vents have been found. These vents produced an output of about 0.25 cubic kilometres (202,678 acre·ft) DRE both in form of lava flows and tephra.
The eruption began in a sub-plinian style creating a column of volcanic gas, pyroclasts and ash about 8 km in height. The erupting N135° trending fissure had two craters of major activity emplaced at each end; the Gris Crater and El Azufral Crater. Volcanic vents of Cordón Caulle that were not in eruption produced visible steam emissions. After this explosive phase the eruption changed character to a more effusive one marked by rhyodacitic blocky and Aa type lava flows emitted from the vents along the N135° trending fissure. A third phase followed with the appearance of short north-north west (N165°) oriented vents transverse to the main fissure which also erupted rhyodacitic lava. The third phase ended temporarily with viscous lava obstructing the vents, but continued soon with explosive activity restricted to the Gris and El Azufral craters. The eruption came to an end on July 22.
• 1960–2011 period
Following the end of the 1960 eruption, Cordón Caulle has remained relatively quiet if compared with the first half of the 20th century. On March 2, 1972 there was a report of an eruption west of Bariloche in Argentina. The Chilean emergency office ONEMI (Oficina Nacional de Emergencia del Ministerio del Interior) organized a flight over the area with two volcanologists aboard. Puyehue and Cordón Caulle as well the Carrán crater were found without activity. From accounts of local inhabitants of the area it is inferred that a small pumice cone was formed around 1990. In 1994 a temporarily emplaced seismic network registered tremors north of Puyehue's cone which reached IV and V degrees on the Mercalli intensity scale. This prompted ONEMI to invoke an emergency action committee, however soon afterward unrest ceased. Between May 4 and 17 of 2011 seismic activity partly attributed to the movements of fluids was detected Southern Andean Volcano Observatory (OVDAS). The activity concentrated around and in Cordillera Nevada caldera and on western Cordón Caulle. This prompted SERNAGEOMIN-OVDAS to declare yellow alert.