Increased activity observed at Calbuco volcano, alert level raised to Yellow, Chile

Increased activity observed at Calbuco volcano, alert level raised to Yellow, Chile

During the last three days, there has been an increase in seismic activity at Chile's Calbuco volcano. A total of 161 volcano-tectonic (VT) earthquakes was recorded at distances between 1 to 4 km (0.62 to 2.5 miles) NW of the crater and between 8 and 10 km (5 and 6.2 miles) deep. In April 2015, a massive eruption took place at this volcano with the plume rising up to 12.1 km (40 000 feet).

Along with VT type earthquakes, SERNAGEOMIN reports, an upward variation of electronic inclinometer (deformation), located 4.5 km W of the crater, shows a cumulative increase of 60 µrad, suggesting an inflationary process.

The above suggests that activity in volcano's deep magma chamber is driving increased seismic activity and crustal deformation. Therefore, the agency has changed the volcanic alert level to Yellow, with particular attention to its evolution.

A high-risk zone is currently within 2 km (1.2 miles) of the crater.

After more than 40 years of sleep, a major explosive eruption started at Chile's Calbuco volcano at 21:05 UTC on April 22, 2015 (18:05 local time). By 22:08 UTC, a plume of smoke and ash rose up to 12.1 km (40 000 feet), Buenos Aires VAAC reported. Aviation Color Code was raised to Red. 

There have been two eruptive pulses that day, pyroclastic flows, lava flows and ash columns, SERNAGEOMIN reported. 

The eruption began after about 2 hours of major seismic activity. OVDAS said they recorded a swarm of VT earthquakes, activity associated with rupture of rock in the Earth's crust caused by magmatic flow. The first major event was M2.5, located 3.3 km (2 miles) west of the crater, at a depth of 7.4 km (4.6 miles).

The national director of SERNAGEOMIN, Rodrigo Álvarez Seguel, said there were hundreds of earthquakes recorded during the two pulses, between 21:00 UTC on April 22 and 01:00 UTC on April 23 and around 04:00 UTC on April 23.

Geological summary

Along with its neighbor Osorno, Calbuco is one of the most active volcanoes of the southern Chilean Andes. The isolated late-Pleistocene to Holocene andesitic volcano rises to 2003 m south of Lake Llanquihué in the Chilean lake district. Guanahuca, Guenauca, Huanauca, and Huanaque, all listed as synonyms of Calbuco (Catalog of Active Volcanoes of the World), are actually synonyms of nearby Osorno volcano (Moreno 1985, pers. comm.).

The 2003-m-high Calbuco is elongated in a SW-NE direction and is capped by a 400-500 m wide summit crater. The complex evolution of Calbuco included edifice collapse of an intermediate edifice during the late Pleistocene that produced a 3 cu km debris avalanche that reached the lake. Calbuco has erupted frequently during the Holocene, and one of the largest historical eruptions in southern Chile took place from Calbuco in 1893-1894 and concluded with lava dome emplacement. Subsequent eruptions have enlarged the lava-dome complex in the summit crater. (GVP)

Featured image: Cabulco by Jason Quinn (Wikimedia)

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