Geologic Background:
Llaima is one of the largest volcanoes in the
Andes, covering an area of about 500 sq km and occupying
a volume of about 400 cu km. It contains two historically
active craters, one at the summit and the other to the
SE. This glacier-capped stratovolcano is one of the most
active in Chile. Summit elevation of 3,125 m. Llaima is a
complex composite-shield volcano, with a buried caldera
and 40 parasitic scoria cones. The Holocene edifice built
primarily of accumulated lava flows was constructed over
an 8-km-wide caldera that formed about 13,200 years ago,
following the eruption of the 24 cu km Curacautin
Ignimbrite. Llaima is chiefly composed of basaltic to
andesitic lava flows, but other noteworthy products
include an older, andesitic pyroclastic-flow deposit (Å24
cu km) and primarily dacitic pumice fall deposits (Å4 cu
km), the most silicic product in the volcano's history.
The pyroclastic flow deposit and dacitic pumice deposit
are older than about 8,800 and 7,200 years, respectively.
The later forms a layer over 50 cm thick in part of the
region between the Chile-Argentina border and Lake
Alumine. Following the end of an explosive stage about
7200 years ago, construction of the present edifice
began, characterized by strombolian, hawaiian, and minor
subplinian eruptions. More than 40 scoria cones dot the
volcano's flanks.
Approximately 10,000 people live in the area.
Melipueco (population 3,000-4,000), ~20 km SSE of the
summit crater at the foot of the volcano, is built on
recent lahar deposits and 30,000 year-old pyroclastic
deposits. Curacautín (population ~10,000) is
roughly 35 km NW of the summit. The nearest city, Temuco
(population 200,000) is 80 km away.
Historic Activity:
- Frequent moderate explosive eruptions with occasional
lava flows have been recorded since the 17th century.
- More the 30 eruptions have been reported from Llaima
since its first historic activity in 1640. The most
vigorous of the 20th century were in 1927 and 1957, while
the most recent ejected a dense ash column on April 20,
1984.
- Approximately 10,000 people live in the area.
Melipueco (population 3,000-4,000), about 20 km SSE of
the summit crater at the foot of the volcano is built on
recent lahar deposits and 30,000 year-old pyroclastic
deposits. Curacautin (population about 10,000) is roughly
35 km NW of the summit. The nearest city, Temuco
(population 200,000) is 80 km away.
Recent Activity:
- A small explosion on Feb. 25, 1990 was followed ty
the ejection of a glowing column from the main
crater.
- Three explosions from the summit crater were observed
between Aug. 23 and Sept. 2, 1992. The explosions fed a
plume 45 km long.
- At about 0600 on May 17, 1994 a
Strombolian-to-subplinian eruption with associated lahars
and flooding occurred. The eruption produced a column
composed of ash, gases, and steam that reached about
4,000 to 5,000 m above the summit. Tephra fell over a
cigar-shaped zone trending about ESE in to Argentina. The
1 mm isopach was about 300 km downwind. Eruption
continued till May 19. On Aug. 25 a new eruptive episode
began with seismic activity and explosions from the
principal crater. Low level activity with eruptive
columns upto 700 m above the crater continued till Aug.
30 when the eruptive columns increased to upto 4 km above
the crater.
- Only fumarolic activity was observed in Feb. 1995. On
Oct. 12, 1995 a M 4.0 earthquake occurred about 160 km
east of Llaima. The following day, Llaima began emitting
steam and ash and on Oct. 21 the largest explosions
occurred. Activity ended on Oct. 22.
- During 1997, basicly stable with occasional phreatic
explosions.
- Small explosions and ash columns in April 1998.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 13, No. 4)
- Global Volcanism Network (V. 15, No. 1 to V. 24, No.
1).
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