Miravalles Volcano, Costa Rica

Volcano Type: Stratovolcano
Volcano Status: Historical
Last Known Eruption: 1946
Summit Elevation: 2028 m 6,653 feet
Latitude: 10.748°N  10°44’54″N
Longitude: 85.153°W 85°9’10″W

Miravalles is a 2028-m-high andesitic stratovolcano that is one of five post-caldera cones along a NE-trending line within the broad 15 x 20 km Guayabo (Miravalles) caldera. The caldera was formed during several major explosive eruptions that produced voluminous dacitic-rhyolitic pyroclastic flows between about 1.5 and 0.6 million years ago. Growth of post-caldera volcanoes in the eastern part of the caldera that overtopped much of the eastern and southern caldera rims was interrupted by edifice collapse that produced a major debris avalanche to the SW. Morphologically youthful lava flows cover the western and SW flanks of the post-caldera Miravalles complex, which rises above the town of Guayabo on the flat western caldera floor. The only reported historical eruptive activity was a small steam explosion on the SW flank in 1946. High heat flow remains, and Miravalles is the site of the largest developed geothermal field in Costa Rica.

Miravalles Volcano

Miravalles (2,208 meters) is an andesitic stratovolcano that is one of five post-caldera cones along a northeast-trending line within the Pleistocene, 15 x 20 kilometer Miravalles caldera. Morphologically youthful lava flows cover the western and SW flanks of the volcano. The only reported historical eruptive activity was a small steam explosion in 1946, although high heat flow remains and a geothermal field is located within the caldera.

Miravalles is situated along the volcanic front of Central America, just southeast of a postulated boundary between eastern Nicaragua and Costa Rican segments of the Cocos-Caribbean subduction zone (Stoiber and Carr, 1973).

Miravalles Volcano

Miravalles Caldera formed approximately 500,000 +/- 150,000 years ago (Tournon, 1984), after eruption of voluminous silicic ash flows. An andesitic stratovolcano of the same name grew within the caldera (Healy, 1969). At least five cones are recognizable in the summit area, distributed along a northeast-trending line (probable fault). The modern intracaldera cone may be the second of two; a previous postcaldera cone was destroyed (R. Fournier, oral commun., 1987). Melson and others (1986) note a preliminary age of 8,000 (?) years B.P. for a major plinian eruption from Miravalles, and an age of 7,000 (?) years B.P. for a large debris avalanche from Miravalles. A geothermal field is situated between the caldera scarp and Miravalles stratovolcano.

Miravalles Volcano

No significant eruption has occurred at Miravalles in historical time. However, on 14 September 1946, a small steam eruption occurred high on the south flank of the volcano, near the summit crater. Weak earthquakes were felt at the time. An explosion crater 20 meters in diameter formed, and steam, mud, and ash were thrown 100 meters high (Hantke, 1951, citing a letter from Sigismund von Preussen of the town of La Barranca). The hydrothermal field is a hot-water-dominated system, with a vapor-dominated cap (few tens of meters thick) in some parts of the geothermal field. Changes in the vapor-dominated cap can give rise to surface hydrologic changes and small blowouts. Fumarolic activity has reportedly decreased in recent years (as of late 1987) (R. Fournier, oral commun., 1987).

Miravalles Volcano

Miravalles Volcano

Originally posted 2010-07-06 10:53:25.