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Report on Irazu (Costa Rica) — March 1992

Bulletin of the Global Volcanism Network, vol. 17, no. 3 (March 1992)
Managing Editor: Lindsay McClelland.

Irazu (Costa Rica) Earthquakes in three epicentral zones; fumarolic activity

Please cite this report as:

Global Volcanism Program, 1992. Report on Irazu (Costa Rica). In: McClelland, L (ed.), Bulletin of the Global Volcanism Network, 17:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199203-345060.

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Irazu

Costa Rica

9.979°N, 83.852°W; summit elev. 3432 m

All times are local (unless otherwise noted)


Fumarolic activity continued in March. The crater lake's water level was several centimeters lower than in February, with an average temperature of 28°C and a pH of 3.7 on 2 April. The 141 earthquakes recorded in March (at station IRZ2, 5 km W of the crater), included M 2.0-2.5 events on 2, 15, and 21-22 March. The larger earthquakes were centered 6-7 km NW, 1.5 km SE, and 3 km NE of the crater, at 0-17 km depth. Low-frequency seismicity continued beneath the crater.

Geologic Background. Irazú, one of Costa Rica's most active volcanoes, rises immediately E of the capital city of San José. The massive volcano covers an area of 500 km2 and is vegetated to within a few hundred meters of its broad flat-topped summit crater complex. At least 10 satellitic cones are located on its S flank. No lava flows have been identified since the eruption of the massive Cervantes lava flows from S-flank vents about 14,000 years ago, and all known Holocene eruptions have been explosive. The focus of eruptions at the summit crater complex has migrated to the W towards the historically active crater, which contains a small lake of variable size and color. Although eruptions may have occurred around the time of the Spanish conquest, the first well-documented historical eruption occurred in 1723, and frequent explosive eruptions have occurred since. Ashfall from the last major eruption during 1963-65 caused significant disruption to San José and surrounding areas.

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI; G. Soto and R. Barquero, ICE; Guillermo Alvarado, GEOMAR, Christian-Albrechts-Universität, Germany; Mario Fernández, Sección de Sismología y Vulcanología, Escuela Centroamericana de Geología, Univ de Costa Rica.