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Report on Irazu (Costa Rica) — February 1992

Bulletin of the Global Volcanism Network, vol. 17, no. 2 (February 1992)
Managing Editor: Lindsay McClelland.

Irazu (Costa Rica) Fumarolic activity in and around crater lake; continued seismicity; deflation

Please cite this report as:

Global Volcanism Program, 1992. Report on Irazu (Costa Rica). In: McClelland, L (ed.), Bulletin of the Global Volcanism Network, 17:2. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199202-345060.

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Costa Rica

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

All times are local (unless otherwise noted)

Fumarolic activity continued in February. Although the water level continued to drop, the crater lake remained larger than it had been in November (figure 5 and table 3). Water temperatures (measured by UNA) on the N side of the lake near the most active subaqueous fumaroles ranged from 37°C to 73°C; bubbling springs near the edge of the lake were <91.5°C (ICE). Subaqueous fumaroles on the SE and NE sides of the lake were less active than those on the N side. Subaerial fumaroles N and NW of the lake had temperatures of 88-90°C and a condensate pH of 4.05. Fumaroles on the NNW and NW flanks of the volcano seemed stable. Temperature decreased with elevation, from a maximum of 95°C at 2,900 m.

Figure (see Caption) Figure 5. Oblique view of the crater lake at Irazú, 25 February 1992. Courtesy of ICE.

Table 3. Crater lake characteristics at Irazú, November 1991 and February 1992. Courtesy of ICE.

[Skip text table]
    Date         Diameter  Max.         Est.     Avg.   Min.
                           Depth       Volume      Temp.   pH

    19 Nov 1991   195 m    14.35 m   280,000 m^3   26.7 C   2.85
    12 Feb 1992   202 m    15.25 m   330,000 m^3   28.3 C   3.23

A monthly total of 234 earthquakes was recorded in February (at UNA station IRZ2, 5 km WSW of the crater), with a maximum of 37 on 21 February. Nine high-frequency earthquakes were recorded in February. Measurements of two geodetic lines across the summit on 13 February indicated contractions of 6.4 ppm in an E-W direction and 15.8 ppm in a N-S direction, since 10 October 1991 (UNA).

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, V. Barboza, and R. Van der Laat, OVSICORI; G. Soto and R. Barquero, ICE.