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Report on Irazu (Costa Rica) — May 1993

Bulletin of the Global Volcanism Network, vol. 18, no. 5 (May 1993)
Managing Editor: Edward Venzke.

Irazu (Costa Rica) Fumarolic activity; no deformation

Please cite this report as:

Global Volcanism Program, 1993. Report on Irazu (Costa Rica). In: Venzke, E (ed.), Bulletin of the Global Volcanism Network, 18:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199305-345060.

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Costa Rica

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

All times are local (unless otherwise noted)

Subaqueous fumarolic activity from the N and SE parts of the crater lake continued in April and May. Bubbling was also observed and heard in the NE part of the lake, and observed in some spots in the N and NW sectors. A new area of N-S oriented bubbling sites was recognized along the N edge of the lake. Maximum lake temperature in the NE sector was 90.6°C. The turquoise-green to yellow-green lake has risen about 20 cm since March. New vegetation was observed growing in the lake. Table 5 summarizes lake characteristics during the last 2 years.

Table 5. Characteristics of the crater lake at Irazú since 17 July, 1991. Courtesy of Gerardo Soto, ICE.

Characteristic 17 Jul 1991 19 Nov 1991 03 Jun 1992 01 Dec 1992 11 May 1993
Diameter (m) 150 195 203 210 203
Maximum Depth (m) 4 14.3 15.4 16.1 15.4
Volume (103 m3) 70.7 263 296 320 296
Water Temp (°C) 30 26.7 26.2 23.6 24.7
Minimum pH 3.8 2.8 4.9 5.6 5.4
Fumarole Temp (°C) 92 92.3 90 92.6 91.5

The steaming ground area on the sediment fan N of the lake remains active, with some noise, and a maximum temperature of 89.5°C. Fumaroles on the NE side, in the dike area, were slightly hotter with a maximum of 91.5°C. The acidity and temperature of hot and cold springs around the volcano were unchanged in May.

Measurements of distance (lineal strain) and areal dilatation showed no changes from 13 January to 7 May. Precision leveling lines located 0.5 km and 3 km SE of the main crater also showed no significant changes. The network of dry-tilt stations detected an average tilt of 20 microradians between January and April on the SE flank, which is probably due to local effects. A seismic station 5 km SW of the active crater recorded four high-frequency events and other smaller magnitude microearthquakes.

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, F. De Obaldía, T. Marino, R. Van Der Laat, V. Barboza, and R. Saenz, OVSICORI; G. Soto, ICE.