The IG reported that in comparison to November the number of long-period earthquakes, which has been shown at Guagua Pichincha to reflect the amount of lava dome growth, and the number of rockfalls decreased in December. Activity has remained relatively constant, with a daily average of 514 earthquakes.

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)