Report on Guagua Pichincha (Ecuador) — 30 April-6 May 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 30 April-6 May 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, 30 April-6 May 2003. Smithsonian Institution and US Geological Survey.
0.171°S, 78.598°W; summit elev. 4784 m
All times are local (unless otherwise noted)
This week Guagua Pichincha was marked by low-to-modest seismicity, which included earthquakes on 30 April and 1 May with magnitudes less than 3. Both had epicenters within an earthquake swarm N of Quito. Episodes of harmonic tremor appeared, most noteworthy on 4 and 5 May with each episode lasting under 40 minutes. Cloud cover obscured the crater area for much of the week (during 30 April and on 2 and 4 May), and civil defense observers monitoring the volcano noted little in the way of sulfurous odors and no noise. Improved visibility on 3 May enabled these observers to see modest fumaroles, with condensate visible at 3 to 100 m heights. This week's observations were similar to those of January, February, and March 2003.
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.