Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that during 23-29 May seismicity at Nevado del Ruiz continued to indicate unrest. Five episodes of drumbeat seismicity (low-energy long-period events) were recorded between 1343 and 1930 on 29 May, likely signifying growing lava domes. Significant amounts of water vapor and gas continued to be emitted. Gas, steam, and ash plumes rose 880 m above the crater rim on 27 May and drifted NW and SW. A thermal anomaly was identified on 28 May. The Alert Level remained at III (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)