Global Volcanism Program | Report on Merapi (Indonesia)

Report on Merapi (Indonesia) — July 2001

Bulletin of the Global Volcanism Network, vol. 26, no. 7 (July 2001)
Managing Editor: Richard Wunderman.

Merapi (Indonesia) Volcanism continues at decreased intensity; Alert reduced from 4 to 2

Please cite this report as:

Global Volcanism Program, 2001. Report on Merapi (Indonesia) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 26:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200107-263250

Merapi

Indonesia

7.54°S, 110.446°E; summit elev. 2910 m

All times are local (unless otherwise noted)

After the large 10 February eruption (see BGVN 26:01), volcanic activity, including lava avalanches and pyroclastic flows, continued but decreased in intensity. Pyroclastic flows entered the Sat, Lamat, Senowo, and Bebeng rivers to a maximum runout distance of 2-3 km. High fumarole temperatures around the summit indicated that magma remained near the surface. The W and S sides of "lava dome 2001" grew and covered "lava dome 1997" to the S. Several fumaroles appeared to mark a fracture in the area of the 10 February eruption. Fractures formed in a similar manner prior to the November 1994 eruption.

The hazard status was at its highest level, 4 (on a scale of 1-4), through the week of 21-27 February 2001. The Alert Level was reduced to 3 the following week, and then to 2 during 7-13 March, where it remained through August.

Over the interval 14 February to 28 August, ash emissions rose up to ~150 m above the summit, and fumaroles emitted gas that rose up to ~950 m above the summit. Superficial earthquakes dominated the seismicity, though over time they continued to decrease in number and amplitude. Observations on 10 and 17 March revealed that high-pressure fumaroles appeared on most of the dome's surface. An observer reported that on 13 April a small amount of ash fell around the Babadan Post Observatory ~7 km W of the volcano. Activity at Merapi increased during 23-29 April, with reports of several medium-sized pyroclastic flows. Table 10 provides a more detailed description of weekly activity at Mt. Merapi from 14 February through 28 August.

Table 10. Summary of activity at Merapi from 14 February through 28 August 2001. Courtesy of VSI.

Interval	Description of Activity
14 Feb-20 Feb 2001	Lava and pyroclastic flows continued but decreased in intensity, pyroclastic flows entered the Sat, Lamat, Senowo, and Bebung rivers. Maximum runut 2-3 km. Flows traveled 1.5-2.5 km to the WSW for 1-2 hours. High temperatures around Merapi indicated that magma was near the surface; the W and S sides of "lava dome bgvn_2001" grew and covered "lava dome 1997" to the S; several fumaroles appeared to mark a fracture along where the 10 February eruption occurred.
21 Feb-27 Feb 2001	Volcanic activity decreased. Daily ash emissions rose to ~150 m above the summit.
07 Mar-13 Mar 2001	Volcanic activity decreased, 100 avalanches per day. Maximum runout of 2.3-2.5 km SW. On 6 March a pyroclastic flow deposited material up to 1.5 km down the Sat river.
14 Mar-20 Mar 2001	Volcanic activity continued, hot avalanches continued to enter the Sat, Senowo, Bebeng, and Lamat rivers. Maximum runout of 2.5 km in the Sat river, pyroclastic flows up to 2.75 km down the Sat, Senowo, and Bebeng rivers. Superficial earthquakes dominated the seismicity but decreased. On 19 March high-pressure fumaroles appeared on most of the dome's surface.
21 Mar-27 Mar 2001	Volcanic activity continued. hot avalanches continued to enter the Sat, Senowo, Bebeng, and Lamat rivers. Maximum runout of 3 km in the Sat river. Pyroclastic flows traveled up to 1 km down the Sat, Senowo, and Bebeng rivers. Superficial earthquakes dominated the seismicity but decreased. On 17 March a summit visit revealed that high-pressure fumaroles remained on most of the dome's surface.
11 Apr-17 Apr 2001	Volcanic activity continued. Lava avalanches continued to enter upstream areas of the Sat, Senowo, Lamat, and Bebeng rivers. Maximum runout of 2.5 km in the Sat river; an observer reported that 10 pyroclastic flows traveled down the Sat, Senowo, and Bebeng rivers, reaching as far as 2.3 km in the Sat river. Fumaroles emitted steam and gas up to 950 m above the volcano's summit; number and amplitude of earthquakes was high but decreasing, seismic activity was dominated by avalanche earthquakes.
18 Apr-24 Apr 2001	Lava avalanches continued to fill the upstream areas of the Sat, Senowo, Lamat, and Bebeng rivers. Maximum runout of 2 km in the Sat river; 11 pyroclastic flows entered the Sat and Lamat rivers, reaching as far as 3 km. Avalanche earthquakes dominated the seismicity but their amplitude and frequency decreased; on 13 April a small amount of ash fell around the Babadan Post Observatory ~7 km W of the volcano.
25 Apr-1 May 2001	Lava avalanches continued to flow down the Sat, Senowo, Lamat, and Bebeng rivers. Maximum runout of 2 km. Fumaroles emitted gas that rose up to 500 m above the summit, seismic activity dominated by earthquakes.
02 May-08 May 2001	Activity increased, with reports of several medium-sized pyroclastic flows. Four pyroclastic flows were observed traveling into the upper reaches of the Sat, Senowo, Lamat, and Bebeng rivers. Maximum runout of 1.8 km in the Sat river; lava avalanches traveled up to 2.5 km down the Sat river. Superficial earthquakes dominated the seismicity.
11 Jul-17 Jul 2001	Lava avalanches. Maximum runout of 2.5 km SW. Low-pressure emissions from fumaroles rose 700 m above the volcano.
18 Jul-25 Jul 2001	52 lava avalanches. Maximum runout of 2.8 km SW. Emissions from low-pressure fumaroles rose to 755 m above the summit.
22 Aug-28 Aug 2001	Lava avalanches. Maximum runout of 2.8 km to the SW. Seismic activity dominated by avalanche earthquakes.

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/); Darwin VAAC, Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, Northern Territory 0811, Australia; Australian Broadcasting Company; Associated Press; Meteorological and Geophysical Agency of Indonesia (Badan Meteorologi dan Geofisika, BMG), Jalan Angkasa I/2 Kemayoran, Jakarta Pusat 10720, Indonesia (URL: http://www.bmg.go.id/).