The IG reported that during the week of 18-24 March a total of 806 long-period earthquakes were registered. However, 460 of those occurred on the 18th along with a moderate ash emission. Long-period event counts were below 20/day as of 21 March. Visual observations made by the Guards of the Refuge revealed that fumarolic activity increased, with higher steam columns on 18, 22, and 23 March, and a stronger sulfur smell until 22 March. No rockfall sounds were heard. The small number of rockfall signals detected as of 26 March suggests that lava dome 9 is stable. The volcano remained at Alert Level Yellow.

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