Laguna Caliente,
Poas Volcano

VOLCANIC FORM: Quaternary Stratovolcano
 
 
 

Latitude	Longitude	Elevation	Lake diameter	Temp. (oC)	pH
10o 12' N	84o 14' W	2300 m	variable  (300 m when full)	58 - 64	< 0

RECENT ACTIVITY:

• constant fumarolic activity and phreatic explosions
• 1953 - magmatic eruption and lake dessication
• intense phreatic activity 1972 - 74 and 1976 - 79

• 1983 - lake volume begins to decrease
• 1986 - lake temperature begins to increase; rate of lake volume decline accelerates
• 1987 - phreatic eruptions from Laguna Caliente, reaching 5 - 100 m in height
• April 1989 - complete dessication of lake; phreatic explosions of mud, sulfur, lake sediments up to 2 km in height
• May 1989 - lake reforms, but dessicates again during the dry seasons of 1990 and 1991

REFERENCES

Laguna Caliente, situated on Poas Volcano in central Costa Rica, is the most acidic and sulfur-rich crater lake in Central America, and probably the world.  Extensive scientific research has been conducted on Laguna Caliente due to its unique chemistry, recent onslaught of volcanic activity, and its status as one of the most extreme environments in the world.

Recent events at Laguna Caliente have led to breakthroughs in our understanding of hydrothermal processes.  Scientists have long suspected that layers of molten sulfur exist at the bottom of many active crater lakes.  When Laguna Caliente dried up in the late 1980's, these suspicions were confirmed with the discovery of molten sulfur lakes and miniature sulfur volcanos on the crater floor of Laguna Caliente.  The exposure of lake sediments at this time provided further insight into lake chemistry.  Sediments of precipitated sulfur, silica, and gypsum were found on the crater floor, indicating saturation of these minerals in the lake waters.  Banding of these sediments records fluctuations in the saturation of gypsum and silica in the water column, caused by corresponding fluctuations in volcanic activity, temperature, and rainfall (Brantley et. al, 1987).

The Extreme Environment of Poas

The gases shooting into Laguna Caliente acidify the lake water and the surrounding environment.  The northwestern flank of Poas Volcano is the area most intensely affected by the acidity.  Vapors of SO₂, CO₂, HCl, HF, and H₂S evading from the crater are carried in a northwestly direction by dominants winds, causing acid rain with pH recorded as low as pH 2.  As a result, the northwest flank of Poas has become almost completely devegetated.  In addition, groundwater seepage from the crater lake discharges at springs on the northwestern flank of Poas, which feed and acidify the Rio Agrio watershed below (Brantley et. al, 1992).
 
 

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1. Title: The chemical and hydrologic structure of Poas Volcano, Costa Rica.
Authors: Rowe, G.L; Brantley, S.L; Fernandez, J.F; Borgia, A.
Source: Journal of Volcanology and Geothermal Research
Volume: 64, no. 3 - 4
Year: 1995

2. Title: Toxic Waters of Poas Volcano.
Authors: Brantley, S.L; Rowe, G.L; Konikow, L.F; Sanford, W.E.
Source: National Geographic Research & Exploration
Volume: 8, no. 3
Year: 1992

3.  Title: Using crater lake chemistry to predict volcanic activity at Poas Volcano, Costa Rica.
Authors: Rowe, G.L; Ohsawa, S; Takano, B; Brantley, S.L; Fernandez, J.F; Barquero, J.
Source: Bulletin of Volcanology
Volume: 54, no. 6
Year: 1992

4.  Title: Poas volcano crater lake acts as a condenser for acid metal-rich brine.
Authors: Brantley, S.L; Borgia, A; Rowe, G.L; Fernandez, J.F; Reynolds, J.R.
Source: Nature
Volume: 330
Year: 1987