Geologic Background:
Poás, one of the most active volcanoes of
Costa Rica, is a broad, well-vegetated volcano with a
summit area containing three craters along a N-S line.
The frequently visited multi-hued summit craters of one
of Costa Rica's most prominent natural landmarks are
accessible by vehicle. The 2708-m-high complex
stratovolcano is constructed within eroded remnants of
nested 7- and 3-km-wide calderas. A N-S-trending fissure
extending to the lower north flank has produced the Congo
stratovolcano and several maars. The southernmost of two
summit crater lakes, Botos, is cold and clear, and last
erupted about 7500 years ago. The other is warm and acid
and has been the site of frequent phreatic and
phreatomagmatic eruptions since the first historical
eruption was reported in 1828. Poás eruptions
often include geyser-like ejection of crater lake water.
Historic Activity:
- Most of the 34 eruptions since 1828 have been from
the northern crater lake, and the 1910 event produce a
geyser >4 km high.
Recent Activity:
- Phreatic eruptions, the first since September 1980,
began in June 1987 and continued through 1997. During wet
periods activity consisted of geyser-like eruptions with
typical eruptions reaching upto 75 meters above the lake.
During dry period, when the lake would dry up the
activity was limited to fumarolic activity.
- Continued fumarolic activity and increased seismicity
were reported during January-June 2000.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 8, No. 3 to V. 14,
No. 11)
- Global Volcanism Network (V. 15, No. 1 to V. 25, No.
3).
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