Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued at moderate levels during 2-8 January. Seismic events indicating rock fracturing increased in both number an intensity. These events were located in areas up to 4 km in various directions from Arenas Crater at depths of 1-7 km. The seismic activity was most notable on 3 and 5 January; the largest earthquake, a M 3.9, was recorded at 1103 on 3 January and felt by officials of the Parque Nacional Natural Los Nevados, SGC personnel in the field, and residents in Manizales (27 km NW). Seismicity associated with ash-and-gas emissions decreased in both size and number. The maximum height of the ash-and-gas emissions was 1.8 km above the summit, recorded on 6 January. Emissions during the week drifted NW, W, and SW, causing ashfall near the volcano and occasionally in Manizales. The Alert Level remained at Yellow, Level III (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)