Based on information from the IG, the Washington VAAC reported that a moderate ash emission at 2145 on 18 March produced an ash cloud that rose to a height of ~5.8 km a.s.l. The ash cloud was not visible on GOES-8 imagery. According to the IG, during the week a large number of earthquakes, especially long-period events, were registered. The detection of a small number of rockfalls confirmed that lava dome 9 continued to slowly grow. 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)