Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued during 15-21 October. The number of seismic events associated with fluid movement increased in both magnitude and number compared to the previous week, especially from seismic signals related to pulsating ash emissions, but were variable between low and moderate levels throughout the week. Webcam images confirmed ash emissions associated with some of these events. The highest temperature recorded for the week was on 16 October, associated with an ash emission at 0452 that rose 1.3 km above the crater. Another ash emission rose 2.2 km above the crater at 1637 on 19 October. Ashfall was reported in Cabaña de Brisas (NW), Aguacerales, and Recreo (Caldas and Tolima). Seismicity associated with rock fracturing remained similar in the number of events and magnitude compared to the previous week, with depths ranging from less than 1 km down to 8 km below the summit. The largest event was an M 1 which was detected at 1725 on 20 October. Sulfur dioxide emissions were variable, and drift directions were not towards measuring stations; satellite measurements indicated a slight decrease in emissions. Low-to-moderate thermal anomalies on the crater floor were identified in satellite data. 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)