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Report on Irazu (Costa Rica) — March 1995


Bulletin of the Global Volcanism Network, vol. 20, no. 3 (March 1995)
Managing Editor: Richard Wunderman.

Irazu (Costa Rica) Lake rises one meter

Please cite this report as:

Global Volcanism Program, 1995. Report on Irazu (Costa Rica) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 20:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199503-345060


Costa Rica

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

All times are local (unless otherwise noted)

"Irazú remains calm [in February]. Fumarolic activity is still weak in the main crater and on the NW flanks. The lake in the main crater has a temperature between 18 and 23°C, and the water surface rose about 1 m with respect to the same date last year. The lake holds an estimated 430 million m3 of water. Acidity and temperature of hot springs surrounding the volcano remain unchanged."

On 17 April Soto added that "tectonic-like seismic events have been recorded in the vicinity of the volcano during 1995 (8 in January, 8 in February, 14 in March . . . )." The hypocenters were located within 20 km of the main crater. The biggest earthquake took place on 21 March, about 15 km from the main crater.

Geological Summary. 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: G. Soto, ICE.