Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that during 23-29 August seismicity at Nevado del Ruiz slightly increased compared to the week before. Significant amounts of water vapor and gas rose from the crater. Thermal anomalies were detected on 24 and 29 August. A period of tremor that started at 1747 on 26 August was associated with an ash emission that rose 900 m above the crater. A gas-and-ash plume, associated with a seismic signal at 1050 on 27 August, was confirmed by a pilot. Based on webcam images and seismic signals, an ash plume rose 1.3 km and drifted NW on 28 August. Gas, steam, and ash plumes occasionally rose 2.3 km above the crater rim and drifted NW and W on 29 August. 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)