The IG indicated that they detected seismic signals from a very minor Guagua Pichincha eruption on 17 April. The volcanologist on duty saw no visual signs of ash, implying that the seismic signals resulted from a very weak eruption with products confined to the summit crater. The IG also noted seeing similar seismic signals sporadically over the previous few days. The signals were thought to result from out-gassing, a class of behavior that if more energetic could generate larger ash clouds of impact to local residents and aviators. The IG also reported several volcano-tectonic earthquakes, seismic signals of rockfalls, and one long-period earthquake.

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.

Sources: Instituto Geofísico-Escuela Politécnica Nacional (IG), Washington Volcanic Ash Advisory Center (VAAC)