Poas, Costa Rica
Location: 10.2N, 84.2W
Elevation: 8,870 feet (2,704 feet)
Poas is a stratovolcano with several eroded calderas, cones, and two
crater lakes at or near its summit. Poas has erupted at least 39 times
since 1828 and is in state of nearly continuous mild activity. Most of
the eruptions are
phreatic,
caused by the interaction
of lava and the water in the crater lake. Explosions vary in strength.
Some explosions eject material about 1,500 feet (500 m) above the lake.
This photo, taken on May 24, 1992, shows one of the craters at the
summit. Note the steam rising from the active crater lake. The lake
(and steam) is very acidic, with a pH less than one. Temperatures as
high as 185 F (85 C) have been measured at the crater lake. Photograph
copyrighted and provided by
Steve O'Meara
of Volcano Watch International.
Boiling crater lake at Poas, 1986. Photograph by Mike Lyvers.
In 1989, the crater lake at Poas gradually drained away. Later,
researchers found a pool of liquid sulphur about 6 feet (2 m) in
diameter. This was the first observation of a liquid sulphur lake on the
surface of the Earth. The sulphur is probably remobilized
fumarole
deposits. Sulphur volcanoes are active on Jupiter's moon
Io.
This photo shows the second crater lake on Poas. This lake is clear.
Photograph copyrighted and provided by Donna Donovan-O'Meara of
Volcano Watch International.
Poas Crater, February 2, 1998. Photo courtesy of Adrian Vargas.
As of late 1995 intense fumarole activity continues at the summit of Poas
near the crater lake.
Sources of Information:
Brown, G., Rymer, H., Dowden, J., Kapadia, P., Stevenson, D., Barquero,
J., and Morales, J.D., 1989, Energy budget for Poas crater lake:
implications for predicting volcanic activity: Nature, v. 339, p. 370-373.
Bulletin of Global Volcanism Network, 1995, v. 20, p. 2.
Global Volcanism Network, 1992, Summary of Recent Activity: Bulletin of
Volcanology, v. 55, p. 615-617.
McClelland, L., Simkin, T., Summers, M., Nielsen, E., and Stein, T.C.,
1989, Global Volcanism 1975-1985: Englewood Cliffs, New Jersey, Prentice
Hall, 655 p.
Neshyba, S., Fernendez, W., and Diaz-Andrade, J., 1988, Temperature
profiles from Poas crater lake: Eos, p. 588.
Oppenheimer, C., and Stevenson, D., 1989, Liquid sulphur lakes at Poas
volcano: Nature, v. 342, p. 790-793.
Simkin, T., and Siebert, L., 1994, Volcanoes of the World: Geoscience
Press, Tucson, Arizona, 349 p.
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