During June 1999-July 2000, Merapi consistently emitted a low-density, sulfur-rich, light-colored gas plume that ranged from 150 to 1,500 m above the summit. Frequent lava avalanches toward the nearby Blongkeng, Lamat, Sat, and Senowo River drainages reached maximum distances of 2 km. Lava avalanches glowed at night, although no incandescence could be observed inside the summit's lava dome. Tiltmeters lacked significant deformational changes, although a summit visit on 13 May 2000 revealed that the 1998 lava dome was growing. Lava avalanches and multi-phase earthquakes dominated seismicity. No lahars were observed during the period.

At the end of July 2000 low-intensity glow from the lava dome was observed. Seismicity increased in the first week of August with a few deep (A-type) and shallow (B-type) earthquakes. Emissions remained similar in consistency to those of the previous months, and rose 160 m above the summit. The hazard level was raised from 1 to 2 (on a 1-4 scale). The following week seismicity continued to increase, exemplified by a M 2.8 B-type event. Gas emissions rose up to 385 m above the summit. During the third week of August, volcanic and seismic activity continued to increase with gas emissions rising 460 m and greater numbers of A- and B-type earthquakes. Surficial events still dominated the overall seismicity. Plumes rose up to 700 m in the final week of August.

Activity remained similar to the previous weeks during September-October. Emissions continued to rise from 250 to 650 m high. The volume of emitted material was estimated to be 169 tons/day at the end of September. Seismicity changed little until late October, when volcanic tremor was recorded.

On 31 October a team from the Merapi Volcano Observatory (MVO) performed summit observations. The team noted that lava avalanches from the 1957 dome had filled the upper stream beds of the Senowo and Trising Rivers. The active 1998 lava dome was lifted on its W side and split in half. A newly formed dome between the two older sides had an elongated E-W-trending shape. Concentric and radial fractures were observed on the N and SW portions of the summit crater, and some fractures showed significant dilation. Radial fractures N of the summit crater and on the floor of Puncak Garuda appeared to have been sutured and then redeveloped to form a normal fault with a total offset of 30 cm. A fracture located between the 1957 and 1948 domes opened 20.5 cm during 14 May-1 November 2000.

High rainfall during the second week in November caused a landslide at the source of the Boyong River near Kaliurang, causing one death. At the end of November, Merapi still emitted a gaseous plume from its summit. Seismographs continued to register A- and B-type earthquakes, although multi-phase earthquakes dominated the record. The volcano remained at Hazard Level 2.

Geological Summary. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities.

Information Contacts: Dali Ahmad, Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).