The following is from the Institute of Volcanology, Boletín de Vulcanología, no. 8.

The block lava flow extruded from the W end of the elliptical summit crater since mid-1979 continued to descend the SW flank through April, causing small forest fires. During a period of increased extrusion in February, the lava had overflowed its channel at about 1,200 m elevation and divided into seven subflows, partially covering three earlier flow deposits.

In early May, lava from the same vent began moving down the W flank. This flow, ~60 m wide and 20 m thick, reached the N rim of Crater A (~1,100 m elevation) by early July. An arm of the flow at 900 m elevation was still advancing on 10 July, although feeding from the vent had stopped.

Another flow, the 33rd since nearly continuous extrusion of block lava began in 1968, started to descend the NW flank in early July. On 11 July its front was at ~1,200 m elevation and was continuing to advance.

Further References. Guendel, F. and Malavassi, E., 1980, La actividad del volcán Arenal entre los días 15 al 20 de Agosto de 1980: Boletín de Vulcanología, no. 9, p. 3-4.

Wadge, G., 1983, The magma budget of Volcán Arenal, Costa Rica from 1968-1980: JVGR, v. 19, p. 281-302.

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 H., Univ. Nacional, Heredia.