Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued during 19-25 March. Seismicity associated with fluid movement decreased in both the number of events recorded and seismic energy released; most of these signals were associated with pulsating emissions of ash and gas. At 0516 on 22 March a seismic signal was associated with an ash emission that rose 1,100 m above the crater and drifted 1,400 m to the SW and W; this was the highest intensity signal this year. Several ash emissions were seen with a webcam. Seismicity associated with rock fracturing decreased in the number of events but increased in seismic energy released. These earthquakes at depths of 1-6 km below the summit were primarily located on the E flank, 3-5 km from the Arenas Crater, with additional events in other areas within 10 km of the crater. The largest event of the period was M 2.0 at 1217 on 24 March. Several 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.

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)