IG reported that during 14-21 May seismic data from Reventador?s network indicated a high level of seismic activity, including explosions, long-period earthquakes, harmonic tremor, and signals indicating emissions.
Weather conditions often prevented views of the summit area, although when clear (during 17-18 and 20-21 May) several ash plumes were visible rising as high as 1 km above the crater rim and drifting W and NW.
Crater incandescence was visible on some mornings and evenings.
On 19 May a 500-m-long pyroclastic flow deposit on the N flank was visible.
Blocks were observed rolling 800 m down the flanks on 21 May.
Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)