Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued at low-to-moderate levels during 19-25 December. Seismic events indicating rock fracturing increased in both number an intensity. These events were located in areas up to 11 km in various directions from Arenas Crater, though mainly on the E flank, at depths of 1-9 km. The seismic activity was most notable during 24-25 December; earthquakes at 1402, 1403, and 1715 on 24 December and at 0813 on 25 December were felt in parts of La Cabaña and the Lagunilla River drainage in the department of Tolima. Seismicity associated with activity at the lava dome had also intensified, beginning at 2301 on 24 December. Ash-and-gas emissions were seismicity detected during the week as well as occasionally visible in webcam images. The maximum height of the ash-and-gas emissions was 1.9 km above the summit, recorded on 22 December. Emissions drifted SE during the first part of the week and SW and NW during the second part of the week, generating ashfall near the volcano and occasionally in Manizales (27 km NW). The Alert Level remained at Yellow, Level III (the second level on a four-level scale), and the public was warned to stay out of the restricted areas around Arenas Crater.

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)