The IG reported that although visual observations were occasionally limited due to cloud cover during 14-20 May, ash and steam plumes from Tungurahua were spotted most days and rose to altitudes of 6-8 km (19,700-26,200 ft) a.s.l. Ashfall was reported in areas within 8 km to the SW and W during 14-15 and 17-18 May. On 15 May, Strombolian activity was observed and blocks rolled down the flanks. On 17 and 18 May, “cannon shots” and explosions vibrated large windows in areas to the SW and W. Roaring noises were occasionally heard. On 18 May, a lahar possibly descended a drainage to the W. On 19 May, numerous incandescent blocks rolled about 1.6 km down the flanks following a large explosion. Roaring and “cannon shot” noises were audible and windows vibrated in nearby areas after the large explosion and several others that followed throughout the night. Ashfall was reported in areas W and NW during 19-20 May.
Based on information from IG, the Washington VAAC reported that on 20 May an ash plume rose to an altitude of 7.9 km (26,000 ft) a.s.l. and drifted NW.
Source: Instituto Geofísico-Escuela Politécnica Nacional (IG) – “Reports provided courtesy of the Smithsonian’s Global Volcanism Program and the US Geological Survey’s Volcano Hazards Program.”