Report on Guagua Pichincha (Ecuador) — 23 April-29 April 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 23 April-29 April 2003
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2003. Report on Guagua Pichincha (Ecuador). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 23 April-29 April 2003. Smithsonian Institution and US Geological Survey.
0.171°S, 78.598°W; summit elev. 4784 m
All times are local (unless otherwise noted)
During the week Guagua Pichincha continued to display seismic unrest, typically with several earthquakes per day but including 16 long-period earthquakes on 26 April. During 23, 24, 26, and 27 April observers on the mountain typically smelled sulfur, but qualitative assessments of fumarolic output varied. In conditions of poor visibility, observers sometimes heard the sound of gases escaping in the crater. In overview, the volcano's activity has not entirely tapered off.
Geologic Background. Guagua Pichincha and the older Pleistocene Rucu Pichincha stratovolcanoes form a broad volcanic massif that rises immediately to the W of Ecuador's capital city, Quito. A lava dome is located at the head of a 6-km-wide breached caldera that formed during a late-Pleistocene slope failure ~50,000 years ago. Subsequent late-Pleistocene and Holocene eruptions from the central vent in the breached caldera consisted of explosive activity with pyroclastic flows accompanied by periodic growth and destruction of the central lava dome. One of Ecuador's most active volcanoes, it is the site of many minor eruptions since the beginning of the Spanish era. The largest historical eruption took place in 1660, when ash fell over a 1000 km radius, accumulating to 30 cm depth in Quito. Pyroclastic flows and surges also occurred, primarily to then W, and affected agricultural activity, causing great economic losses.