Logo link to homepage

Report on Merapi (Indonesia) — June 2002

Bulletin of the Global Volcanism Network, vol. 27, no. 6 (June 2002)
Managing Editor: Richard Wunderman.

Merapi (Indonesia) Pyroclastic flows and lava avalanches occur during February-June 2002

Please cite this report as:

Global Volcanism Program, 2002. Report on Merapi (Indonesia). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 27:6. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200206-263250.

Volcano Profile |  Complete Bulletin


Merapi

Indonesia

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

All times are local (unless otherwise noted)


From 25 February through 16 June 2002 a generally white, variably dense, low-pressure plume rose 150-820 m above the summit of Merapi. Seismicity was dominated by avalanche earthquakes (table 14). During the week of 25-31 March, one shallow volcanic earthquake was reported. The Volcanological Survey of Indonesia (VSI) reported that Merapi emitted varying amounts of SO2 (table 15).

Table 14. Seismicity (low-frequency, avalanche, and multiphase) and crater characteristics at Merapi during 25 February-16 June 2002. Magnetic field strength was measured at Pusang-Lempong and is reported in nanoteslas (nT). "--" indicates that the information was not reported. Courtesy VSI.

Date Low-frequency events Avalanche events Multiphase events Magnetic field strength Gendol crater Woro crater
25 Feb-03 Mar 2002 -- -- -- -- -- 571°C
04 Mar-10 Mar 2002 -- 666 -- -- -- --
11 Mar-17 Mar 2002 5 652 -- -- -- --
18 Mar-24 Mar 2002 1 609 -- -- -- --
25 Mar-31 Mar 2002 60 575 -- -- -- --
01 Apr-07 Apr 2002 135 539 1 -- -- --
15 Apr-21 Apr 2002 46 364 -- 3.09 nT -- --
22 Apr-28 Apr 2002 19 367 1 0.32 nT -- --
29 Apr-05 May 2002 9 383 13 -3.22 nT 737-742°C 421-434°C
06 May-12 May 2002 13 353 -- 4.64 nT 737-746°C 398-431°C
13 May-19 May 2002 2 345 2 8.28 nT 734-748°C 406-430°C
20 May-26 May 2002 -- 308 15 -1.02 nT 734-749°C 421-431°C
27 May-02 Jun 2002 8 310 6 -1.47 nT 620-750°C 354-430°C
03 Jun-09 Jun 2002 9 268 6 -1.65 nT 741-756°C 423-435°C
10 Jun-16 Jun 2002 -- 281 5 1.65 nT 736-755°C 423-434°C

Table 15. COSPEC-measured SO2 gas emission at Merapi during 3 March-16 June 2002. "--" indicates that the information was not reported. Courtesy VSI.

Date Average SO2 emission (ton/day) Range (ton/day) Max. avg. (ton/day)
03 Mar-10 Mar 2002 156 96-254 196
11 Mar-17 Mar 2002 131 87-173 138
18 Mar-24 Mar 2002 146 103-206 --
25 Mar-31 Mar 2002 133 74-172 136
01 Apr-07 Apr 2002 107 73-145 108
15 Apr-21 Apr 2002 124 105-167 --
22 Apr-28 Apr 2002 155 97-219 182
29 Apr-05 May 2002 156 109-245 173
06 May-12 May 2002 166 123-210 169
13 May-19 May 2002 90 43-182 145
20 May-26 May 2002 140 64-206 160
27 May-02 Jun 2002 131 62-216 167
03 Jun-09 Jun 2002 141 85-196 167
10 Jun-16 Ju 2002 125 42-218 161

In total, 69-108 lava avalanches per week were observed during mid-February through late March. The avalanches generally traveled 2.5-2.75 km towards the upstream ends of the Senowo, Sat, and Lamat rivers, and partly to the Bebeng river. During 25 February-3 March, a total of four minor pyroclastic flows traveled to the upstream part of the Bebeng river to a maximum distance of 1.0 km (3 on 25 February and 1 on 3 March). Field observations of the summit on 28 February revealed very thin solfatara sublimation at Gendol and Woro craters. Temperatures at the craters were 354-755°C (table 14). No further pyroclastic flows occurred until 29 and 30 March, when 7 and 2 flows, respectively, traveled 1.8 km down to the upstream ends of the Sat and Senowo rivers. Low-frequency (LF) earthquakes, which had been recorded during the previous few weeks, increased (table 14), and high-intensity rain fell but did not trigger lahars.

Table 15 shows Merapi's SO2 fluxes. The molar concentrations of volcanic gases from Gendol crater on 28 February were as follows: 0.21% H2, 0.02% (O2 + Ar), 0.54% N2, 3.87% CO2, 0.01% CO, 1.00% H2S, 5.49% HCl, 88.86% H2O. One pyroclastic flow was reported during 25-31 March.

During early April, two minor pyroclastic flows traveled 1.3 km toward the Sat river. Activity at Merapi increased significantly; LF earthquakes reached 135 events within the week. The most intense rain was ~65 mm/hour near the Babadan post observatory on 4 April, but it did not trigger lahars. On 14 April, two minor pyroclastic flows reached 1.8 km maximum distance. Seismicity began to decrease but was still higher than normal. Deformation data from Reflector 4 at the Babadan post observatory indicated 7 mm of deflation, and the lava dome morphology did not change.

No further pyroclastic flows were reported through at least mid-June. Seismicity and general activity at Merapi was reportedly decreasing. Merapi remained at Alert Level 2 throughout the report period.

Geologic Background. 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 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive 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 during historical time.

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