Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued during 4-10 February. Seismic data indicated that events associated with fluid movement increased in both number and intensity compared to the previous week. Webcam images, observations from residents, and reports from the Parque Nacional Natural Los Nevados confirmed some ash emissions and higher-temperature ejecta were associated with some of these events. Notably, Long-duration seismic signals associated with continuous ash emissions were only recorded on 4 February. Gas-and-ash plumes rose as high as 1.5 km above the summit and drifted NW, W, and SW; taller plumes, recorded during 9-10 February, rose as high as 2 km as they drifted downwind. Seismicity associated with rock fracturing was similar in number but higher in magnitude compared to the previous week. The earthquakes were located below Arenas Crater and the NE, E, and ESE flanks within 13 km, and had depths of 1-9 km. Two earthquakes were felt by residents on 6 February: a M 2 that occurred at 0131 and was located 6 km E of the crater at a depth of 3 km and a M 2.3 that occurred at 2024 and was located 5 km ESE of the crater at a depth of 4 km. Low-energy thermal anomalies on the crater floor were identified in satellite data. Sulfur dioxide emissions detected in satellite data continued to be significant. 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, not to spend long periods of time on the Murillo-Cerro Gualí Road, and to avoid drainages in the high-threat zones.

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)