Geologic Background:
Lascar is the most active volcano of the
northern Chilean Andes. The andesitic-to-dacitic
stratovolcano contains six overlapping summit craters
along a NE-SW trend. Prominent lava flows descend its NW
flanks. An older, higher stratovolcano 5 km to the east,
Volcan Aguas Calientes, displays a well-developed summit
crater and probable Holocene lava flow near its summit
(de Silva and Francis 1991). The growth of the Lascar II
stratovolcano ended with eruption of the Tumbres scoria
flow about 9000 years ago, after which growth of Lascar
III began, producing three overlapping craters.
Historic Activity:
- At least 14 eruptions occurred between 1848 and
1974.
Recent Activity:
- Lascar has been almost continuously active since its
1986 eruption, with episodes of dome growth in the summit
crater and small-to-moderater explosions.
- In 1986 single explosive events occurred on September
14, 15, and 16. Prior to the eruptions, a prominent steam
plume, larger than the normal plume, had been present but
no significant seismic activity had been recorded.
- Three explosions in July 1988 sent columns as high as
3 km. Active lava dome in summit crater and steam and ash
emissions were observed from Feb. to April 1989. Strong
steam plumes in Dec. 1989.
- Explosive eruption on Feb. 20, 1990 produced tephra
cloud. By November Lascar had returned to its normal
fumarolic activity.
- An explosion on Oct. 21, 1991 produced a dark gray
column which reached roughly 2000 m high. A second
smaller explosion occurred the next day.
- A new dome was observed forming in crater during late
February and early March 1992. Continued fumarolic
activity. In late March the dome was about 180 m across
and 40 m high. During mid May several large explosions
occurred along with accompaning tephra plumes.
- The largest historical eruption of Lascar began late
on April 18, 1993 and sent ash 20 to 22 km above the
5450-m high crater rim the following day. Pyroclastic
flows traveled 7.5 km NW and light ashfall (<0.1 mm)
were reported in Buenos Aires, Argentina, 1500 km SE of
the volcano. The initial explosions may have been related
to the partial destruction of the dome that had filled
the crater in March 1992. Pyroclastic flow activity
occurred much of the day on April 19. Major explosive
activity resumed early on April 20 and was accompanied by
pyroclastic flows. By the morning of April 21 activity
had returned to normal fumarolic activity. Small
explosions occurred on the 22th, 23rd, 26th and 29th of
April. Large tephra plume to the SSE covered
approximately 20,000 sq km with at least 1 mm of ash and
over 850,000 sq km, including pars of N-central
Argentina, S Paraguay, Uraguay, and S Brazil, were
covered by a thin (<0.1 mm) deposit of ash.
Overflights of the crater identified a new lava dome
(estimated volume of 4,600,000 cu m) on the bottom of the
crater, filling a much larger portion of the crater than
either the 1989 or 1992 domes. The dome grew in <40
hours from April 24-26. By May 19, the dome had begun to
collapse and by Nov. 5 a funnel-shaped depression had
reached an estimated depth of 50-100 m below the surface
of the dome. On Dec. 17, 1993 an eruption produced a
column that rose about 8,000 m above the crater.
- A small short-lived eruption occurred on Feb. 27,
1994. Continued fumarolic activity. Renewed Vulcanian
activity during July 20-26 generated plumes up to Å9,000
m altitude, Å4,000 m above the summit. Two small phreatic
eruptions were observed in Nov. 1994.
- Small eruptive plumes were reported in 1995 on May 10
and June 20.
- Small ash eruption on July 20-21, 2000.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 11, No. 8 to V. 14,
No. 12)
- Global Volcanism Network (V. 15, No. 1 and V. 25, No.
6).
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