INGEOMINAS reported that during 13-14 April seismicity associated with fluid movement beneath Nevado del Ruiz was detected along with volcano-tectonic earthquakes. The earthquakes were located NW of Arenas Crater at depths between 5 and 9 km; the largest was a M 2.6, felt by officials of Los Nevados National Park in the area of Brisas (50 km SW). During the early morning of 14 April webcams recorded a gas-and-ash plume that rose 630 m and drifted NW. On 15 April a M 3 volcano-tectonic earthquake was located NW of Arenas Crater at a depth of 6.6 km. Later that day a M 2.5 volcano-tectonic earthquake was located again NW of Arenas Crater at a depth of 5.78 km. On 16 April at 0714 a M 3.2 earthquake was located in the same area at a depth of 6.22 km. Earthquakes continued to be felt by officials in the National Park. A gas-and-steam plume rose 1 km above the crater and drifted SW. Sulfur dioxide emissions were significant and deformation was detected. The Alert Level remained at III (Yellow; "changes in the behavior of volcanic activity").

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)