Tremor was recorded at Guagua Pichincha for ~16 hours after a phreatic eruption on 26 November. Signals from a relatively high number of rockfalls were recorded on seismographs, which is normal after an explosion. Two new craters formed during the explosion N of the 1981 crater. The following day, dark steam was observed rising 5 m above the craters. Volcanic and seismic activity remained at low levels after the 27th, with only low-level fumarolic activity occurring.

Geological Summary. Guagua Pichincha and the older Pleistocene Rucu Pichincha stratovolcanoes form a broad volcanic massif that rises immediately W of Ecuador's capital city, Quito. A lava dome grew at the head of a 6-km-wide scarp formed during a late-Pleistocene slope failure ~50,000 years ago. Subsequent late-Pleistocene and Holocene eruptions from the central vent consisted of explosive activity with pyroclastic flows accompanied by periodic growth and destruction of the lava dome. Many minor eruptions have been recorded since the mid-1500's; the largest took place in 1660, when ash fell over a 1,000 km radius and accumulated to 30 cm depth in Quito. Pyroclastic flows and surges also occurred, primarily to then W, and affected agricultural activity.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)