Based on seismicity during 19-25 October, OVDAS-SERNAGEOMIN reported that the eruption from the Cordón Caulle rift zone, part of the Puyehue-Cordón Caulle volcanic complex, mostly continued at a low level. Seismicity did increase during the last few days of the reporting period.

Plumes visible with an area web camera rose no higher than 2 km above the crater during 19-20 October. A small plume visible in satellite imagery on 19 October drifted 50 km E and a diffuse ash plume drifted 150 km NE and SE. On 20 October a small plume drifted 70 km E.

At night on 22 October incandescence emanated from the crater, possibly from active lava flows reported during the previous few days. At 0311 an explosion generated a plume that rose 4.5 km above the crater as well as increased incandescence from the crater. An ash plume observed in satellite imagery drifted 120 km W and NW, and a diffuse ash plume drifted 250 km NE and SE. During the day a white plume rose 3 km above the crater. Satellite imagery showed a plume that drifted 125 km NE, then dissipated NE and SE. On 24 October, a plume rose 6 km above the crater. Satellite imagery showed a plume drifting 125 km NE and a diffuse ash plume drifting 280 km in the same direction. The next day white plumes did not rise higher than 7.5 km above the crater and satellite imagery showed a plume that drifted 100 km NW and SW. The Alert Level remained at Red.

Geological Summary. 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 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 volcano was constructed above a 5-km-wide caldera and is capped by a 2.4-km-wide 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 wide volcano-tectonic depression, is the largest active geothermal area of the southern Andes volcanic zone.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)