Global Volcanism Network Bulletin v. 19, no. 7, July 1994

Merapi (Indonesia)  Increased deformation precedes a nuee ardente
Marapi (Indonesia)  Eruption sends ash column to ~6 km above sea
      level; summary of 1993 activity

central Java, Indonesia (7.54S, 110.44E)

A nuee ardente erupted around 1400 on 16 July 1994, an event
preceded by a clear increase in tilt several days before the
eruption. Figure 13 shows tilt measurements during the interval
1-18 July. One set of measurements came from a site on Merapi's
summit (Goa Jepang, ~2,900 m elevation); the other set of
measurements came from a cave on Merapi's S flank (~1,000 m

The daily temperature variation in the cave is <1 deg C, suggesting
little influence from temperature there (left-hand scale). The
daily record of tilt varied significantly less at the cave site
(typically <100 frad) than at the summit site (typically ~150
frad), an observation consistent with the more stable temperature
in the cave.

Tilt began increasing at both sites roughly 5 days prior to the
eruption. During this interval the tilt at both sites correlated
consistently overall, and moderately at the finer-scale. Tilt
ceased to track consistently near the end of the eruption, when the
flank site underwent a dramatic decrease, a turn-around that began
prior to the end of the eruption. Summit tilt measurements in
January 1993 were similar to those presented here but then
measurements at the cave site were a rarity, leaving the increased
tilt without confirmation.

Merapi is one of the most active volcanoes in Indonesia; it sits
immediately N of the large city of Yogyakarta; at least 50,000
people live adjacent to its SW slope. The stratovolcano has an
exposed, summit lava dome, the source of abundant glowing blocks
that continue to tumble down its SW slope. In historical time,
instability of the growing dome has led to nuees ardentes that have
caused many fatalities, disasters described in many popular books
on volcanology. Merapi is occasionally confused with Marapi

Information Contacts: Arnold Brodscholl, Geophysics Laboratory,
Gadjah Mada University, FMIPA-UGM, Sekip Unit III, P.O. Box BLS 21,
Yogyakarta 55281, Indonesia; Subandryo, VSI, Yogyakarta, Indonesia;
Barry Voight, Dept. of Geoscience, Pennsylvania State University,
503 Deike Bldg., University Park, PA 16802 USA.

Figure 13. Tilt at Merapi recorded at both the summit and in a cave
on the S flank. Courtesy of Arnold Brodscholl.