Geologic Background:
The 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 was constructed to the NW
of the older Chato volcano, which contains a 500-m-wide
summit crater. The activity of Chato ended about 3500
years ago, and the oldest known Arenal rocks are only
2900 years old. 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.
The volcano lies directly adjacent to Lake Arenal, a
dammed reservoir for generating hydroelectric power. The
volcano has been watched by many tourists from a mountain
lodge 2.8 km S of the vent that enables visitors to hear,
to see, and occasionally to smell its dynamism. The town
of La Fortuna is located 7 km NE of the volcano. The
Arenal Observatory is 2.7 km S of the summit.
Historic Activity:
- No known activity within historic times prior to
1968.
- Arenal's most recent eruptive period began with a
major explosive eruption in 1968. Continuous explosive
activity accompanied by slow lava effusion and the
occasional emission of pyroclastic flows has occurred
since then from vents at the summit and on the upper
western flank. An explosive episode devastated the W
flank and caused 78 deaths.
Recent Activity:
- Activity has been nearly continuous since 1968 with
strombolian eruptions and extrusion of more than 40
discrete lava flows from the summit area.
- Small pyroclastic flows in 1999 and 2000.
- On August 23, 2000 a large pyroclastic flow was fed
by a substancial ash column.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 8, No. 3 to V. 14,
No. 11)
- Global Volcanism Network (V. 15, No. 1 to V. 25, No.
8).
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