Geologic Background:
Volcan Copahue is a composite cone constructed
along the Chile-Argentina border within an 8-km-wide
caldera formed 0.6 million years ago near the NW margin
of the Pliocene, 20 x 15 km Del Agrio caldera(4.5 million
years old). The eastern summit crater, part of a
2-km-long, ENE-WSW line of nine craters, contains a briny
crater lake (also referred to as Del Agrio) and displays
intense fumarolic activity. Infrequent explosive
eruptions have been recorded since the 18th century.
Copahue is on the Chilean/Argentinian border, at the
northern end of the NNE-SSW trending Liquine-Reloncavi
fault zone and at or just south of the intersection of
that fault zone with a transverse, NW-SE fault zone.
The Trapa-Trapa caldera (7 km in diameter) forms a
semicircle north of the currently active
andesitic-dacitic composite volcano whose summit includes
9 mostly ice-filled craters in a ENE-WSW line about 2 km
long. Intense solfataric activity has occurred in the
eastern crater, which is filled with hot briny water.
Historic Activity:
- The last eruption from Copahue was reported in 1937,
and other eruptions may have occurred in 1867, 1759, and
1750.
- A strong increase in solfataric activity took place
in 1941-44.
Recent Activity:
- A series of explosion started on July 31, 1992.
Associated with the explosions were small debris flows,
ash falls, and strong sulfur odors. Tephra from repeated
moderate explosions was generally carried eastward, and
mudflows extended several kilometers down streams
draining the glaciated summit area. Airfall from the
largest explosion, on Aug. 2, covered about 88 sq. km.
and debris flows were generated within the valleys of the
Agrio (Argentina) and Lomin (Chile) rivers.
- An eruption began on July 1, 2000. This eruption is
considered to be the most vigorous activity in the past
century. Activity was continuing in September.
Data Sources:
- Global Volcanism Network (V. 17, No. 6 to V. 25, No.
9).
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