Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued during 18-24 June. The number of seismic events associated with fluid movement increased in both magnitude and number compared to the previous week. There was an increase in the number of long-duration seismic signals. Some of these signals were associated with ash emissions observed by officials at Parque Nacional Natural de Los Nevados and area residents. Seismicity associated with rock fracturing was stable in both the number and magnitude of events compared to the previous week; these earthquakes at depths of 1-7 km below the summit were primarily located within 10 km of Arenas Crater, particularly to the SE and ESE. The largest event was an M 1.1 which was detected at 2358 on 18 June and was located at a depth of 2 km. Seismic signals indicating lava-dome activity notably increased; on 24 June a period of dome-related seismicity was characterized as having the longest duration and highest number of events since 2015, the year this type of seismicity was first detected. Sulfur dioxide emissions were variable and gas plumes rose as high as 1.4 km above the crater rim and drifted NW, W, and SW. Thermal anomalies on the crater floor were identified in satellite data, though weather conditions often inhibited views. The Alert Level remained at Yellow (the second level on a four-level scale), and the public was warned to stay out of the restricted areas around Arenas Crater.

Geological Summary. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Source: Servicio Geológico Colombiano (SGC)