Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued during 31 December 2024-6 January 2025. The number of seismic events associated with fluid movement decreased in both number and intensity compared to the previous week, though seismicity indicating continuous ash-and-gas emissions increased (notably on 6 January). Webcam images confirmed several ash emissions and higher-temperature ejecta associated with some of these events; plumes drifted NW, W, and WSW following ash-and-gas emissions that rose 2-2.1 km above the summit at 0814 on 1 January and at 0003 on 3 January. Seismicity associated with rock fracturing decreased in both number and magnitude compared to the previous week. The earthquakes were located below Arenas Crater and the NE, E, SE, SW, and NW flanks within 11 km, and had depths less than 5 km. The largest event, an M 1.2, was recorded at 1551 on 2 January and was located 3 km SW of the crater at a depth of 4 km. Low-energy thermal anomalies on the crater floor were identified in satellite data when weather permitted. Sulfur dioxide emissions detected in satellite data were higher than the previous weeks. 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)