Servicio Geológico Colombiano’s (SGC) reported that the eruption at Nevado del Ruiz continued during 11-18 April and was characterized by gas, steam, and ash emissions, thermal anomalies at the lava dome in Arenas Crater, and elevated seismicity. Seismic signals indicating rock-fracturing events continued to be located 2-6 km SW of Arenas Crater at depths of 2-4 km, though on 12 and 16 April signals were also located in the NE sector of the volcano at depths of 0.5-5 km. The number of daily events fluctuated through the week. Additionally, signals indicating fluid movement fluctuated in intensity and were associated with daily ash emissions. On 11 April ash-and-gas plumes rose as high as 2.5 km above the crater rim and drifted SW and NW, causing ashfall in the municipalities of Villamaría (Caldas) and Filandia (Quindío). Ash-and-gas plumes that rose as high as 1.8 km drifted SW and NW on 12 April, and 1.5 km high plumes drifted SW on 13 April. During 0759-1113 on 14 April and from 1515 on 14 April to 1257 on 15 April seismicity activity intensified and corresponded to continuous ash emissions that rose as high as 1.5 km and drifted SW. These emissions were visible from the municipalities of Murillo and Manizales. Later that day gas-and-ash plumes rose to 1.6 km and drifted NW. According to a news article 87 people had self-evacuated after the government called for the voluntary evacuation of around 2,500 families on 5 April. The Alert Level remained at Orange, Level II (the second highest level on a four-level 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.

Sources: Servicio Geológico Colombiano (SGC), CNN