GEOLOGIC HISTORY
Merapi, one of the most active volcanoes in Indonesia,
dominates the landscape immediately north of the city of
Yogyakarta in one of the world's most densely populated
areas. The steep-sided modern edifice, its upper part
unvegetated due to frequent eruptive activity, was
constructed to the SW of an arcuate scarp cutting the eroded
older Batulawang volcano. Pyroclastic flows and lahars
accompanying growth and collapse of the steep-sided active
summit lava dome have devastated cultivated lands on the
volcano's western-to-southern flanks and caused many
fatalities during historic times
Historic Activity:
- At least 60 eruptions have occurred from 1006 to
1968.
- Since 1953 activity has been characterized by
extrusion of lava into the summit crater, wtih periodic
lava dome collapse and nuee ardente formation.
Recent Activity:
- Following an explosion in 1969 a lava dome began to
grow in the crater. Growth has continued to occur
periodically since then with incandescent rockfalls from
the dome when it becomes oversteepened.
- During November 1986 a lava flow from the base of the
dome slowly advanced out of the crater on to the SW
flank. The slowly growing lava dome in the summit crater
reached 6,600,000 cubic meters by late 1989, a size
described as "critical" for the collapse-prone dome.
- Seismicity began to increase in late December, 1991,
and glowing rockfalls from a new summit lava dome were
first seen on Jan. 20, 1992. Avalanche- generated
pyroclastic flows began on Jan. 31, were most frequent in
early February, then decreased. No pyroclastic flows have
been observed since mid April. Dome growth continued
through late July, reaching an estimated volume of
10,500,000 cu m. The 1992 dome covered the remnant of the
1957 lava dome that had formed the NW crater rim. Shallow
earthquakes occurred on August 26, 1992 and pyroclastic
flows occurred shortly thereafter. Additional small
pyroclastic flows occurred on August 28 and during Nov.
Pyroclastic flows were seen between the end of December
and Feb. 6, 1993.
- Seismic and visual activity had decreased since the
beginning of 1993. In the interval from May-November
1993, 3-10 avalanches/month were reported as compared to
10 avalanches/day during dome growth in 1992 and early
1993.
- The number of pyroclastic flows and glowing rockfalls
began to increase in January 1994 and outward tilt was
recorded. Based on these monitoring data the
Volcanological Survey of Indonesia raised the hazard
status to "First Alert Level". An eruption on July 16 was
preceded by increased tilt several days before the
eruption. Collapse of the active summit dome on Nov. 22
produced pyroclastic block-and-ash flows and glowing
surges that traveled SSW up to 7.5 km from the summit. As
of Nov. 28, 41 people had died and another 43 vere at
hospitals in serious condition.As of Dec. 19 the death
toll was 60. Continuing small eruptions through Dec. 7
sent pyroclastic flows up to 1.5 km down the Boyong
River.
- During August-October 1995 pyroclastic flows
continued flowing down the Boyong River and others
entered the Krasak and Bebeng Rivers and reached upto 2.5
km from source.
- Ash emissions and lava avalanches from March to May
1999.
- During 2000 a new lava dome formed resulting in lava
avalanches and landslide.
- During Jan 2001 the new dome continued to grow,
resulting in over 30 pyroclastic flows. A major eruption
occurred on Feb 10 with the collapse of the 1998 lava
dome. Activity continued at a declining rate for the
remainder of the year, with small dome collapses and
pyroclastic flows.
Data Sources
- Smithsonian's SEAN Bulletin (V. 1, No. 6 to V. 14,
No. 11)
- Global Volcanism Network (V. 15, No. 7 to V. 26, No.
10).
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