Recent activity at Copahue through December 2016 consisted of gas and steam plumes with minor amounts of ash. Eruptive activity ended in late December 2016, but ash emissions began again in early June 2017. Distinct ash emissions decreased after July, and crater incandescence was no longer reported. However, persistent tremor and degassing with sporadic ash continued through 2017.

This report through December 2017 is based on information obtained from the Buenos Aires Volcanic Ash Advisory Center (VAAC), the Southern Andes Volcanological Observatory (OVDAS), and the Servicio Nacional de Geología y Minería (National Geology and Mining Service) (SERNAGEOMIN). Volcano Alert Levels are set by SERNAGEOMIN (on a four-color scale) and by the Chilean Oficina Nacional de Emergencia del Ministerio del Interior (National Office of Emergency of the Interior Ministry) (ONEMI), on a three-color scale), for alerts to individual communities in the region.

OVDAS-SERNAGEOMIN reported that webcams recorded an increase in ash emissions on 4 June 2017. There were no significant changes in the magnitude or number of earthquakes recorded by the seismic network. The report noted that due to inclement weather making visual observations difficult, the observatory did not know if the ash emission began in the early hours of 4 June, or the day before. On the same day, OVDAS-SERNAGEOMIN raised the Alert Level to Yellow; ONEMI set a Yellow Alert for the communities of Villarrica, Pucón, and Curarrehue in La Araucanía, and for Panguipulli in Los Ríos.

During 5-15 June 2017 the seismic network detected long-period earthquakes. Gas plumes constantly rose from El Agrio crater and on several days contained ash. The highest plume, detected on 5 June, rose 300 m and drifted E.

The Buenos Aires VAAC reported that on 1 July the webcam recorded a steam-and-gas plume with minor ash near the summit. Webcam and satellite images analyzed by the Buenos Aires VAAC showed that during 7-8 July steam plumes with minor amounts of ash rose to altitudes of 4-4.3 km altitude and drifted ESE. During 16-17 July similar plumes rose to altitudes of 3-3.4 km and drifted N and NW. According to ONEMI, OVDAS-SERNAGEOMIN reported that during 16-31 July surficial activity had decreased. The webcam recorded constant gas emissions with sporadic ash rising no more than 280 m from El Agrio crater. Crater incandescence was visible during clear weather. The Alert Level remained at Yellow, and SERNAGEOMIN recommended no entry closer than 1 km of the crater. ONEMI continued an Alert Level of Yellow for the municipality of Alto Biobío.

In August, activity continued to decrease. Degassing was constant and sometimes contained ash. Plumes did not exceed 500 m in height and incandescence was absent. During the first half of the month, 23 seismic events occurred, 20 of which were volcanic-tectonic; tremor associated with the degassing was constant. During the latter half of August, SERNAGEOMIN lowered the Alert Level to Green. Because gas emissions continued, SERNAGEOMIN suggested that the public stay beyond a radius of 500 m of the active crater.

SERNAGEOMIN reports for November and December indicated that some seismic activity continued. In November, 337 earthquakes occurred, 261 of which were volcanic-tectonic. Tremor associated with degassing continued, and incandescence was reported on some days. Based on satellite and webcam views, the Buenos Aires VAAC reported that during 21 and 24-27 November diffuse steam plumes containing minor amounts of ash rose and drifted E and NE. Plumes rose to altitudes of 3.3-3.6 km during 25-26 November.

On 2 December, one volcanic-tectonic earthquake occurred at 1758 local time. More than 20 volcanic-tectonic earthquakes occurred about 2245 on 5 December. The SERNAGEOMIN report for December noted persistent tremor associated with gas and ash emissions, and that constant gas plumes with sporadic ash rising to a maximum height of 1,300 m above the summit was recorded by the web camera. The Alert Level remained Green through December 2017.

Geological Summary. Volcán Copahue is an elongated composite cone constructed along the Chile-Argentina border within the 6.5 x 8.5 km wide Trapa-Trapa caldera that formed between 0.6 and 0.4 million years ago near the NW margin of the 20 x 15 km Pliocene Caviahue (Del Agrio) caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains a briny, acidic 300-m-wide crater lake (also referred to as El Agrio or Del Agrio) and displays intense fumarolic activity. Acidic hot springs occur below the eastern outlet of the crater lake, contributing to the acidity of the Río Agrio, and another geothermal zone is located within Caviahue caldera about 7 km NE of the summit. Infrequent mild-to-moderate explosive eruptions have been recorded since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.

Information Contacts: Servicio Nacional de Geología y Minería, (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); Oficina Nacional de Emergencia - Ministerio del Interior (ONEMI), Beaucheff 1637/1671, Santiago, Chile (URL: http://www.onemi.cl/); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/).