Chilean authorities increased the alert level for Puyehue-Cordón Caulle volcano to Yellow (2 of 4) on June 20, 2018, following increased seismic activity detected under the volcano since the beginning of the month. The last eruptive phase of this volcano started on June 4, 2011 and ended in April 2012 (VEI 5).
According to parameters observed between June 1 and 15, 2018, a total of 272 earthquakes were recorded under the volcano, of which 48 were classified as long-period (LP) earthquakes associated with dynamics of fluids inside the volcano.
215 earthquakes were volcano-tectonic, associated with the movement (injection or withdrawal) of magma. These were located 0.6 km (0.4 miles) west of the center of 2011 eruption, at a depth of 2.8 km (1.7 miles).
In addition, the seismic network registered 9 hybrid earthquakes of moderate magnitude, associated with evidence of deformation. Hybrid earthquakes took place 5.2 km (3.2 miles) SE of the center of 2011 eruption, at a depth of 1.7 km (1 mile).
Authorities said this is a preventive alert and called on the community to get informed through the official channels.
“We are monitoring the Puyehue-Cordón Caulle Volcanic Complex 24 hours a day. Our specialists have adequate technology to monitor volcanic activity. The important thing is that the various institutions of the Civil Protection System have technical information on what is happening to make it available to the public,” the National Director of SERNAGEOMIN, Mario Pereira, said.
The Puyehue-Cordón Caulle volcanic complex (PCCVC) is a large NW-SE-trending late-Pleistocene to Holocene basaltic-to-rhyolitic transverse volcanic chain SE of Lago Ranco.
The 1799-m-high (1.1 miles) Pleistocene Cordillera Nevada caldera lies at the NW end, separated from Puyehue stratovolcano at the SE end by the Cordón Caulle fissure complex.
The Pleistocene Mencheca volcano with Holocene flank cones lies NE of Puyehue. The basaltic-to-rhyolitic Puyehue volcano is the most geochemically diverse of the PCCVC. The flat-topped, 2236-m-high (1.4 miles) volcano was constructed above a 5-km-wide (3.1 miles) caldera and is capped by a 2.4-km-wide (1.5 miles) Holocene summit caldera.
Lava flows and domes of mostly rhyolitic composition are found on the E flank. Historical eruptions originally attributed to Puyehue, including major eruptions in 1921-22 and 1960, are now known to be from the Cordón Caulle rift zone.
The Cordón Caulle geothermal area, occupying a 6 x 13 km (3.7 x 8 miles) wide volcano-tectonic depression, is the largest active geothermal area of the southern Andes volcanic zone.