Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued during 19-25 November. The number of seismic events associated with fluid movement decreased in number but increased in magnitude compared to the previous week. Additionally, the number of low-level, long-duration events increased. Webcam images confirmed several ash emissions and higher-temperature ejecta associated with some of these events, though weather clouds sometimes obscured views. Seismicity associated with rock fracturing remained similar in number but decreased in magnitude compared to the previous week. The earthquakes were less than M 1, located below Arenas Crater and the SSW, NE, and SE flanks within 10 km, and had depths of 1-7 km. Low-energy thermal anomalies on the crater floor were identified in satellite data when weather permitted. Gas plumes rose up to 1.3 km above the crater rim and drifted SW on 21 and 24 November. Sulfur dioxide emissions detected in satellite data were similar to previous weeks. 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, not to spend long periods of time on the Murillo-Cerro Gualí Road, and to avoid drainages in the high-threat zones.

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)