Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued during 9-15 July. The number of seismic events associated with fluid movement decreased in both magnitude and number compared to the previous week but were variable throughout the week. Through webcams and visual observations by officials at Parque Nacional Natural de Los Nevados, several as emissions associated with these events were confirmed. Seismicity associated with rock fracturing decreased in the number of events but maintained similar magnitudes compared to the previous week; these earthquakes at depths of 1-7 km below the summit were primarily located within 4 km of Arenas Crater and the NE sector. The largest events were M 1.2 which were detected at 0319 on 13 July (about 1 km NW and 2 km deep) and 1222 on 14 July (to the N and 4 km deep). Seismic signals indicating lava-dome activity increased but remained of short duration and low energy level. Sulfur dioxide emissions were variable, and gas plumes rose as high as 1.5 km above the crater rim and drifted NW, W, and WSW. 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)