Based on seismic measurements, the IG reported that an eruption may have occurred at 0030 on 8 December. Throughout the day seismic activity continued at a decreased rate and no ash was observed. The fact that the Washington VAAC did not detect ash in GOES-8 imagery during cloudless conditions supported the theory that an ash-producing eruption did not occur. The IG stated that the high number of earthquakes indicated that lava dome 9 continued to slowly grow.

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)