Report on Irazu (Costa Rica) — August 1992
Bulletin of the Global Volcanism Network, vol. 17, no. 8 (August 1992)
Managing Editor: Lindsay McClelland.
Irazu (Costa Rica) Seismicity decreases; gas emission continues
Please cite this report as:
Global Volcanism Program, 1992. Report on Irazu (Costa Rica). In: McClelland, L (ed.), Bulletin of the Global Volcanism Network, 17:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199208-345060.
9.979°N, 83.852°W; summit elev. 3432 m
All times are local (unless otherwise noted)
Activity in the main crater remained stable in August, with weak vapor emission from sediment fans on the N side of the crater lake and active fumaroles in the NE part of the lake. The lake remained green, and its level has varied by only a few centimeters in recent months. Erosion of the crater walls carried sediment to fans on its N, W, and E sides. Temperature and pH of springs monitored around the volcano had not changed from previous months. The number and energy release of local seismic events have decreased considerably in the past 3 months. A UNA seismic station (IRZ2) 5 km WSW of the main crater registered 27 small events in August, down from 33 in July.
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: G. Soto and R. Barquero, ICE; E. Fernández, J. Barquero, and V. Barboza, OVSICORI.