Geologic Background:
El Misti, Peru's most well-known volcano, is a
symmetrical stratovolcano with nested summit craters that
towers above the city of Arequipa. The modern symmetrical
cone, with a small 1.5-km-wide summit caldera, caps an
older Pleistocene volcano that collapsed, producing
debris avalanches to the west and SW. A large scoria cone
has grown with the 830-m-wide outer summit crater of El
Misti. At least 20 tephra-fall deposits have been
documented during the past 14,000 years, and a
pyroclastic flow traveled 12 km to the south about 2,000
years ago. El Misti's most recent activity has been
dominantly pyroclastic, and strong winds have formed a
parabolic dune field of volcanic ash extending up to 20
km downwind.
Historic Activity:
- The last strong eruption of El Misti occurred between
1438 and 1471 (the reign of the Inca Pachacutec); several
weeks of vigorous tephra emission forced residents of the
region to flee.
- Several smaller explosive eruptions have been
reported since then, most recently in 1870, but some were
probably only periods of increased fumarolic
activity.
Recent Activity:
- New fumaroles were discovered in the summit crater in
July 1985.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 9, No. 5 and V. 10,
No. 12).
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