Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued during 30 April-6 May. The number of seismic events associated with fluid movement remained stable at low-to-moderate levels, though the signal increased in magnitude. Some of these signals were associated with pulsating emissions of ash and gas; ash plumes rose as high as 2 km above the summit on 30 April and drifted NW and WNW. Seismicity associated with rock fracturing was stable in both the number and magnitude of events; these earthquakes at depths less than 5 km below the summit were primarily located within 5 km of Arenas Crater, particularly to the E. The largest event was an M 1.2 which was detected at 1842 on 1 May. Several 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)