Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico and Sismológico de Manizales reported that during 8-14 July gas-and-steam plumes rose 600 m above Nevado del Ruiz’s crater and drifted NW. Sulfur dioxide emissions were significant. Seismicity was dominated by volcano-tectonic signals. The earthquakes were located NE, S, and SW of Arenas Crater; the largest was a M (local) 2.1 located SW of Arenas Crater at a depth of 3.4 km. Shallow seismicity associated with fluid movement occurred S and SE of the crater. During 11-12 July continuous volcanic tremor associated with emissions was detected; ashfall was reported in Los Nevados Natural Park and in some parts of Manizales (30 km NW). The Alert Level remained at III (Yellow; "changes in the behavior of volcanic activity").

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)