On 10 May Servicio Geológico Colombiano’s (SGC) reported that during the previous week the number of seismic signals indicating both rock fracturing and fluid movement at Nevado del Ruiz had increased compared to the week before. Several episodes of drumbeat seismicity were recorded on 5 and 8 May, indicting growth of the lava dome. Some low-temperature thermal anomalies were also identified at Arenas Crater. Gas-and-ash emissions were periodically visible in webcam images. A small ash emission on 3 May caused minor ashfall in the municipalities of Manizales (25 km N), Dosquebradas (40 km W), Santa Rosa, and Pereira (40 km WSW). At 0857 on 9 May an ash plume drifted NW, W, and SW, causing ashfall in Manizales, Villamaría (28 km NW), and Chinchiná (30 km WNW) in the department of Caldas, and in Pereira, Dosquebradas, and Santa Rosa de Cabal (33 km W) in the department of Risaralda. 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.

Source: Servicio Geológico Colombiano (SGC)