Report on Irazu (Costa Rica) — July 1992
Bulletin of the Global Volcanism Network, vol. 17, no. 7 (July 1992)
Managing Editor: Lindsay McClelland.
Irazu (Costa Rica) Continued thermal activity and seismicity; crater lake rises
Please cite this report as:
Global Volcanism Program, 1992. Report on Irazu (Costa Rica). In: McClelland, L. (ed.), Bulletin of the Global Volcanism Network, 17:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199207-345060.
9.979°N, 83.852°W; summit elev. 3432 m
All times are local (unless otherwise noted)
The level of the turquoise-green crater lake continued to rise. The subaqueous fumaroles on the lake's N and SE sides remained active, but fumarolic activity on the N and NW sides of the crater has diminished considerably. The seismic station (IRZ2) 5 km WSW of the main crater registered 33 low-frequency events in July, about the same number as in June. On 9 July at 0627, a M 2.5 earthquake occurred 6.6 km SE of the main crater at 5 km depth.
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.