On 15 February Servicio Geológico Colombiano’s (SGC) reported that during the previous week seismicity at Nevado del Ruiz was at similar levels to the weeks before, characterized by periods of continuous volcanic tremor, harmonic tremor, long-period events, and very-long-period earthquakes, indicating movement of fluids. These earthquakes occurred in the vicinity of Arenas Crater. Additional earthquake signals indicating rock fracturing were located at Arenas Crater and in areas to the SE and had decreased in size and frequency since the previous week. Two periods of “drumbeat” seismicity, indicting growth of the lava dome, were recorded on 10 February. Gas-and-ash emissions were periodically visible in webcam images. A small explosion on 11 February generated an ash plume that rose above the crater. According to the Washington VAAC an ash plume rose to 7 km (23,000 ft) a.s.l. and drifted N at 1130 that same day. The Alert Level remained at 3 (Yellow; the second lowest level on a four-color scale).

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.

Sources: Servicio Geológico Colombiano (SGC), Washington Volcanic Ash Advisory Center (VAAC)