Geologic Background:
Cerro Hudson is the southernmost volcano in the
Chilean Andes related to subduction of the Nazca plate
beneath the South American plate. The massive,
1905-m-high Cerro Hudson covers an area of 300 sq km.
Cerro Hudson lies in a stretch of the southern Andes that
has relatively few active volcanoes. A N-S fault (one of
many extending much of the length of Chile) passes
several kilometers west of Cerro Hudson. The ice-filled,
10-km-wide caldera of the remote Cerro Hudson volcano was
not recognized until its first 20th century eruption in
1971. The caldera is drained through a breach on its NW
rim, which has been the source of mudflows down the Rio
de Los Huemeles. Two cinder cones occur north of the
volcano and another occupies the SW flank. Hudson has
been the source of several major Holocene explosive
eruptions. An eruption about 6700 years ago was one of
the largest known in the southern Andes during the
Holocene; another eruption about 3600 years ago also
produced more than 10 cu km of tephra. Preliminary
tephrachronology indicates that in the last 7,000 years
Hudson has had at least 3 large magnitude eruptions.
Minor Plinian eruptions had a recurrence interval of 500
to 1,000 years.
Historic Activity:
- Hudson last erupted in 1971, producing an ash cloud 7
km high, and extruding lava that melted glacial ice,
triggering a large mudflow down the Huemules River
valley. Following the 1971 eruption, ice melt from
continued fumarolic activity accumulated within the
caldera until January 1973, when it abruptly flowed down
the Huemules River valley.
Recent Activity:
- Eruptive activity began late on August 8, 1991 with a
phreato-magmatic explosion that produced a column 7-10 km
high. Immediately following the initial explosion, a
dense, ash laden column formed, reaching about 12 km.
Activity steadily decreased through Aug. 11 with columns
declining to about 6 km. A second, larger eruption
started on August 12 and continued till August 15 with
produced a major tephra plume reaching 16-18 km altitude.
Tephra fall was reported in the Falkland Island a 1000 km
to the SE. Eruptions were basaltic to andesitic in
composition.
- The eruption produced 1 to 2+ cu. km. (dense rock
equivalent) of magma. The initial Aug. 8-9 eruption was
from a basaltic dike through a fissure 4 km long,
trending through the NW rim of the 10 x 7 km, ice-filled
caldera. The basalt erupted both as a lava fountain and
phreatomagmatically, producing a tephra and ash column 12
km high, scoria flows that covered 10 sq. km. of the
western caldera floor and an unknown area outside of the
caldera, a 4 km long lava flow over Huermules glacier,
and floods down the Rio Sorpresa and Rio Huemules
valleys, and a low volume tephra fall deposit north of
the volcano.
- A small eruption occurred several days before Oct. 6,
1991, emitting ash that was carried 8 km SE.
- In Feb. 1995 there were reports of noises and
sulfurous odors reaching inhabitants 40 to 75 km from the
volcano. Also reports of river level rising and satellite
images showing thermal anomaly in the caldera.
Overflights revealed no surface indications of
activity.
Data Sources:
- Global Volcanism Network (V. 16, No. 7 to V. 20, No.
2).
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