Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that during 4-10 October the number and magnitude of volcano-tectonic earthquakes at Nevado del Ruiz increased compared to the previous week. Long-period and very-long-period signals as well as pulses of tremor were also recorded. Significant amounts of water vapor and gas rose from the crater. At 1746 on 5 October an episode of volcanic tremor was associated with ash emissions recorded by area webcams. Gas, steam, and ash plumes rose 2 km above the crater on 8 October and drifted NE. 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)