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Report on Arenal (Costa Rica) — April 1986


Scientific Event Alert Network Bulletin, vol. 11, no. 4 (April 1986)
Managing Editor: Lindsay McClelland.

Arenal (Costa Rica) Continued lava production; avalanches from flow fronts

Please cite this report as:

Global Volcanism Program, 1986. Report on Arenal (Costa Rica) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 11:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198604-345033


Costa Rica

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

All times are local (unless otherwise noted)

"Arenal remained very active, with emission of lava from Crater C at 1,450 m elevation. Lava advanced towards the N, NW, W, SW, and S, with flow fronts reaching 900 m elevation. Frequent avalanches, from continuous to every 15 minutes or so, occurred from the flow fronts. Sporadic explosions ejected pyroclastic materials, with some blocks and bombs falling at 800 m elevation. Ash was carried by winds, mainly toward the W and SE, to 4 km distance. Gas and vapor emission was continuous."

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: J. Barquero and E. Fernández, OVSICORI.