Servicio Geológico Colombiano’s (SGC) reported that during 8-14 November seismicity associated with rock fracturing at Nevado del Ruiz increased in number and energy compared to the previous week. Some of the signals were associated with gas-and-ash emissions. The hypocenters were located 0.6-7 km deep. The largest event was an M 3.1 that was recorded at 0225 on 10 November at a depth of 3.6 km below the crater and 2.7 km SW of the crater. The Washington VAAC reported ash plumes that rose to 6.4-7.3 km altitude (21,000-24,000 ft) and drifted S and SE on 11 November, based on satellite and webcam images. During 13-14 November ash plumes rose to 6.7 km altitude (22,000 ft) and drifted NE based on satellite and webcam images. Several low-to-moderate thermal anomalies in Arenas Crater were identified in satellite images. Gas-and-steam plumes (mainly sulfur dioxide) continued to be emitted, rising as high as 1.8 km above the summit on 8 November and drifting NW, SW, SE, and NE. The Alert Level remained at 3 (Yellow; the second lowest level on a four-color scale).

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.

Sources: Servicio Geológico Colombiano (SGC), Washington Volcanic Ash Advisory Center (VAAC)