IG reported that during the previous months activity at Reventador was characterized by an average of 50 explosions per day and long-period earthquakes indicating fluid movement. Ash plumes from explosions rose as high as 2 km above the crater rim, and small pyroclastic flows descended the flanks in almost all directions. However, at 1701 on 22 June the pattern of activity changed. Seismic signals indicating emissions became continuous, and spasmodic tremor emerged which was composed of numerous small explosions. Concurrent to the change in seismicity, small-to-moderate pyroclastic flows descended 4 km down the NE flank, and plumes with low-to-moderate ash content rose 2.5 km and drifted W. Pyroclastic-flow deposits were also noted in the upper basin of El Reventador river, E of the cone. During 22-23 June incandescent blocks rolled 500 m down the flanks, steam-and-ash plumes rose 2 km, and several pyroclastic flows traveled 900 m NE. Cloud cover sometimes prevented visual observations during 24-27 June though sometimes gas-and-ash plumes were seen rising no higher than 500 m above the crater rim. Incandescent blocks continued to descend the flanks, traveling as far as 650 m. “Cannon shot” sounds were heard at night during 24-25 June. During 26-27 June several episodes of incandescence at the crater were noted, and a lava flow traveled 2 km down the NE flank.

Geological Summary. Volcán El Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic stratovolcano has 4-km-wide avalanche scarp open to the E formed by edifice collapse. A young, unvegetated, cone rises from the amphitheater floor to a height comparable to the rim. It has been the source of numerous lava flows as well as explosive eruptions visible from Quito, about 90 km ESE. Frequent lahars in this region of heavy rainfall have left extensive deposits on the scarp slope. The largest recorded eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN)