SERNAGEOMIN reported that the eruption in Villarrica’s summit crater intensified during 20-26 September. A long-period (LP) earthquake associated with fluid movement, recorded by the seismic network at 0914 on 20 September, was accompanied by a short grayish-brown pyroclastic emission that rose 50 m above the crater rim and drifted SSE. Whitish gas emissions were visible before and after the event. Another LP event was recorded at 1012 on 21 September, but weather conditions prevented visual observations.

A sustained increase in seismicity was recorded throughout the day on 23 September. Several discrete, low-altitude ash emissions were visible rising to heights less than 150 m above the crater rim and drifting SE. Some notable emissions occurred at 0841, 0910, 1251, 1306, 1312, 1315, and 1324. Diffuse gas emissions were visible in webcam images. During 23-24 September RSAM values reached high levels, Strombolian explosions ejected material onto the upper flanks near the crater, and thermal anomalies intensified. On 24 September the Volcanic Alert Level was raised to Orange (the third level on a four-level scale) and the exclusion zone was increased to an 8-km radius. SENAPRED maintained the Alert Level at Yellow (the middle level on a three-color scale) for the communities of Villarrica, Pucón (16 km N), Curarrehue, and Panguipulli. During 24-26 September seismicity stabilized then decreased slightly, though it remained at high levels. During the early morning of 25 September Strombolian explosions ejected incandescent material up to 250 above the crater rim and onto the upper flanks, mainly to the NW. Strombolian explosions continued to be recorded on 26 September. A continuous ash emission drifted ENE for a period of 50 minutes. Thermal anomalies continued to be identified in satellite data.

Geological Summary. The glacier-covered Villarrica stratovolcano, in the northern Lakes District of central Chile, is ~15 km south of the city of Pucon. A 2-km-wide caldera that formed about 3,500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesite cone at the NW margin of a 6-km-wide Pleistocene caldera. More than 30 scoria cones and fissure vents are present on the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Eruptions documented since 1558 CE have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

Sources: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Sistema y Servicio Nacional de Prevención y Repuesta Ante Desastres (SENAPRED)