Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued at low levels during 23-29 January. Seismic events indicating rock fracturing increased in number, though the intensity of the signals was similar to the previous week. These events were mainly located in areas up to 6 km to the NE and SSE of Arenas Crater, and at depths of 1-7 km. The largest event, a M 1.3, occurred at 2105 on 24 January and was located about 1 km SSE of the crater and at a depth of 3 km. Seismicity associated with gas-and-ash emissions remained at similar numbers as the previous week but were less intense. Gas-and-ash emissions drifted NW and N and rose to a maximum height of 1.8 km above the summit, recorded on both 25 and 29 January. Sulfur dioxide emissions varied but decreased overall. 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)