Conical Volcan Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1657-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.
Arenal's most recent eruptive period began on July 29, 1968 at 7:20 AM when "Cerro" Arenal--as it was called by local residents--explosively blew the west side off the volcano. Two villages at the foot of the volcano-- Pueblo Nuevo and Tabacon--were completely destroyed and 78 people died. Between July 29 and 31 three new craters were formed on the western flank of the volcano and a fifteen-square kilometer area (5.8 square miles) was devastated.
