Geologic Background:
Villarrica, one of Chile's most active
volcanoes, rises above the lake and town of the same
name. It is situated at the intersection of the major
NNE-SSW Liquine-Reloncavi transcurrent fault zone and a
northwest trending alignment of volcanoes with Villarrica
at its center. It is the westernmost of three large
stratovolcanoes that trend perpendicular to the Andean
chain. The symmetrical, mafic cone of Villarrica has
largely filled a 9 km x 6 km diameter caldera, which
formed during or following eruption of silicic dacite.
The rim of a smaller caldera appears at the 2400-m level
on Villarrica stratovolcano as a slight irregularity in
that volcano's symmetry .The 6-km wide caldera formed
during the late Pleistocene, >0.9 million years ago.
While the 2-km-wide postglacial caldera is located at the
base of the presently active, dominantly
basaltic-to-andesitic cone at the NW margin of the
Pleistocene caldera. About 25 scoria cones dot
Villarica's flanks. Plinian eruptions and pyroclastic
flows have been produced during the Holocene from this
dominantly basaltic volcano, but historical eruptions
have consisted largely of mild-to-moderate explosive
activity with occasional lava effusion. Lahars from the
glacier-covered volcano have damaged towns on its flanks.
Historic Activity:
- Villarrica has erupted over 60 times since 1558.
Villarrica erupts frequently without regard to the length
of time since the previous eruption. Typically, eruptions
exhibit subterranean noises, loud and repeated bangs from
the crater, columns of smoke and vapor, fountains of
incandescent debris, ash columns that rise several
kilometers above the summit, and lava flows.
Recent Activity:
- During activity, which began in October 1984 and
continued through November 1985, Strombolian activity
ejected incandescent material to 100-400 m heights. Lava
travelled about 2 km down the NE flank, melting a channel
through glacial ice and producing several small lahars.
Mudflows down the volcano's steep flanks have caused
fatalities during 4 eruptions this century.
- An increase in fumarolic activity and weak explosions
were observed in the crater during August-September 1991.
On Aug. 30 small ash emissions and continuous explosions
were observed. A weak emission of gray ash and a white
gas plume 1 km high were observed on Sept. 17, 1991.
- Phreatic explosions 300 to 400 m high were observed
from a town 15 km from the volcano on Sept. 11, 1992.
Explosions began on Nov. 3, 1992, and built two small
pyroclastic cones. Weak explosions during December.
- In Sept, 1994, over a Å 3.5 hours period, four
explosions and accompaning ash falls were reported.
Between Dec. 25-30, 1995 several dark plumes of ash were
reported erupted from the crater.
- Seismicity at Villarrica increase above background
starting on Sept. 7, 1996. On Sept. 14, emissions of gas
and ash were generated by four rhythmic explosions.
Seismicity again began to increase on Sept. 26 and
continued into October. During October and November a
rapidly convecting lava lake nearly filled the central
crater pit.
- Strombolian explosions from a vent on the crater
floor continued through August 1997.
- Activity in crater from late March through November
1998
- Small ash explosions mid- 1999.
- Continuing activity of summit lava lake from January
through Decmber 2000. Increase in ash eruptions in Sept
and Oct. Explosions from Oct to Dec.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 8, No. 10 to V. 10,
No. 11)
- Global Volcanism Network (V. 16, No. 8 to V. 25, No.
10).
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