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Report on Arenal (Costa Rica) — September 1990


Bulletin of the Global Volcanism Network, vol. 15, no. 9 (September 1990)
Managing Editor: Lindsay McClelland.

Arenal (Costa Rica) More frequent explosions; lava extrusion continues

Please cite this report as:

Global Volcanism Program, 1990. Report on Arenal (Costa Rica) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 15:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199009-345033


Costa Rica

10.463°N, 84.703°W; summit elev. 1670 m

All times are local (unless otherwise noted)

Strombolian, effusive, and fumarolic activity continued through September. During August, lava descended the SW and S flanks and small nuées ardentes originating from the crater were periodically observed. Explosive activity produced an ash column (to 1 km above the crater) that was carried predominantly NW, W, and SW by the wind, and ejected blocks and bombs to 800 m from the crater. Flank vegetation continued to be affected by ashfall. Heavy rainfall and steep slopes caused small avalanches in the Calle de Arenas (E flank) and Guillermina (NE flank) quebradas (streams), and the Agua Caliente river (SW flank).

Explosive activity increased . . . to a maximum of 63 explosions/day, on 18 September. An average of 40/day were recorded during the last half of September. On 27 September, an increase in volcanic tremor was detected, with episodes of continuous tremor lasting up to 10 hours.

Geological Summary. Conical Volcán Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1670-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. Arenal lies along a volcanic chain that has migrated to the NW from the late-Pleistocene Los Perdidos lava domes through the Pleistocene-to-Holocene Chato volcano, which contains a 500-m-wide, lake-filled summit crater. The earliest known eruptions of Arenal took place about 7000 years ago, and it was active concurrently with Cerro Chato until the activity of Chato ended about 3500 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. An eruptive period that began with a major explosive eruption in 1968 ended in December 2010; continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows characterized the eruption from vents at the summit and on the upper western flank.

Information Contacts: G. Soto and R. Barquero, ICE; J. Barquero, E. Fernández, and V. Barboza, OVSICORI.