Report on Irazu (Costa Rica) — June 2000
Bulletin of the Global Volcanism Network, vol. 25, no. 6 (June 2000)
Managing Editor: Richard Wunderman.
Irazu (Costa Rica) Feeble microseismicity continues into early 2000
Please cite this report as:
Global Volcanism Program, 2000. Report on Irazu (Costa Rica). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 25:6. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200006-345060.
9.979°N, 83.852°W; summit elev. 3432 m
All times are local (unless otherwise noted)
This report covers January-June 2000. In January seismographic station IRZ2 (5 km SW of the active crater) recorded seven small-magnitude earthquakes. During February and March no activity was recorded. In April, May, and June, respectively, IRZ2 recorded 10, 12, and 30 earthquakes. The latter month included low-frequency events.
During May the level of the crater lake decreased by 50 cm. During the dry period, the lake's color was yellow/green, and a significant amount of algae covered its surface. On the lake's NE and S shore lines constant bubbling continued; the temperature of the lake was 18°C. The E, N, and W crater walls continued sliding toward the lake. Fumarolic activity on the NE flank continued at a low level.
In June the crater lake's surface rose 40 cm in comparison to May. The lake color was now green and its surface was still covered by abundant algae. The NE crater wall continued sliding, partly covering some fumaroles while others completely disappeared. Also, along the NE wall three new thermal features appeared with temperatures that fluctuated between 22 and 54°C. On the NE and S shore the bubbling stopped during June.
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: Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.