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 Merapi 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 elevation). 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 (Sumatra). 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.