Report on Galunggung (Indonesia) — June 1982

Scientific Event Alert Network Bulletin, vol. 7, no. 6 (June 1982)
Managing Editor: Lindsay McClelland.

Galunggung (Indonesia) Explosions continue; most of 1918 dome destroyed; 40,000 evacuated

Please cite this report as:

Global Volcanism Program, 1982. Report on Galunggung (Indonesia). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 7:6. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.SEAN198206-263140.

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Galunggung

Indonesia

7.25°S, 108.058°E; summit elev. 2168 m

All times are local (unless otherwise noted)


Intermittent explosions began 5 April, destroying ~ 90% of Gunung Jadi, the lava dome extruded . . . in 1918. Lahars and nuées ardentes flowed SE through the breach onto the upper portion of the major prehistoric landslide deposit. The highest reported ash column reached 16.5 km, pitting the windshield of a passing airplane. Ash fell as far away as the Yogyakarta-Solo area, ~ 300 km to the E.

The ten eruptive episodes that had occurred as of late June were separated by quiescent periods that ranged from three days (early in the eruption) to three weeks (before the 24-27 June explosions). Nuées ardentes produced by the first five explosions (5, 8, 20-21, and 24 April, and 6 May) traveled a maximum of 5 km. After the 6th eruptive episode, on 13 May, ~ 90-95% of the 1918 lava dome was still intact, with destruction limited to weak zones on its NW and SE margins, but the next explosions, on 17-19 May, left only ~10% of the old dome in the crater.

The 24-27 June explosions dropped 8-18 cm of ash and lapilli on villages 7-10 km W of the volcano, destroying hundreds of houses. Indonesian newspapers reported that people a few km from the crater heard thundering sounds and saw glow over the volcano before the explosions began. Residents of Tasikmalaya (17 km ESE of the volcano) saw incandescent tephra ejection at 1900, 1910, and 1930. At 2050, a British Airways jumbo jet with 240 persons on board, flying roughly 150 km WSW of Galunggung at ~11 km altitude, encountered an ash cloud that stalled all four of its engines and abraded its windshield and wing surfaces. St. Elmo's fire was noted in the cockpit as the jet flew through the ash cloud. The aircraft lost 7.5 km of altitude before the engines could be restarted, but it landed safely in Jakarta. Light ashfall began about midnight in Bandung, stopping by morning, but the city remained in semi-darkness into the afternoon. Images from the Japanese GMS and the NOAA 7 polar orbiter showed that the eruption cloud moved W then curved toward the S with its distal end reaching a point roughly 850 km S of Galunggung.

A similar explosion occurred at about 1000 on 25 June. Five hours later, data from infrared satellite imagery showed that the top of the cloud produced by this explosion had a temperature of -65°C, corresponding to an altitude of ~13.5 km, well below the tropopause at 15.3 km (-76°C). Winds at 13.5 km were from the NNE, and satellite images showed that the cloud moved toward the SSW to roughly 900 km from the volcano, before dissipating by 1500 the next day.

Chemical analyses show a consistent decline in SiO2 content, from 55.7 weight % in samples from the first explosion to 49.2% in the June tephra. A significant increase in MgO, FeO, and CaO content was also noted between early April and late June. The seismic record has shown continuous tremor (amplitude 2 mm at magnification 2,000x) and specific precursory signatures before explosions. According to a preliminary estimate of the VSI, magma was located about 3 km below the surface in late June. The VSI indicated that the interval from 27 June until the next explosive episode might last 1-3 weeks but that quiescent intervals may tend to increase in length.

Three additional explosions were seen on satellite imagery 13-15 July. On a GMS image returned 13 July at 2300, a plume that appeared to be several hours old extended S from Galunggung, then curved SE. A Singapore Airlines jumbo jet carrying 230 passengers flew into this cloud at about 9 km altitude. Three of its four engines stalled, but after losing ~2.4 km of altitude, pilots restarted one engine and landed safely in Jakarta. Air traffic has now been rerouted away from Galunggung. A much smaller cloud emerged from the volcano shortly before 0700 the next day and moved SE. By 1900, the distal end of the first plume was about 850 km ESE of Galunggung and the second, narrower, plume extended nearly 600 km SE. A third explosion at about 1800 on 15 July appeared comparable in size to the first. By 2300, the cloud had moved ~ 500 km to the S.

A volcanic hazard map prepared in 1974 has been used successfully by volcanologists and civil authorities to delineate danger zones at Galunggung, including areas at risk from lahars produced by rainfall on recent ejecta. After the 24-27 June activity, the number of evacuees had climbed to 40,000, living in temporary government barracks. Of the 27 deaths associated with the eruption, only three have been caused directly by pyroclastic material.

Geologic Background. The forested slopes Galunggung in western Java are cut by a large horseshoe-shaped caldera breached to the SE that has served to channel the products of recent eruptions in that direction. The "Ten Thousand Hills of Tasikmalaya" dotting the plain below the volcano are debris-avalanche hummocks from the collapse that formed the breached caldera about 4200 years ago. Although historical eruptions, restricted to the central vent near the caldera headwall, have been infrequent, they have caused much devastation. The first historical eruption in 1822 produced pyroclastic flows and lahars that killed over 4000 people. More recently, a strong explosive eruption during 1982-1983 caused severe economic disruption to populated areas near the volcano.

Information Contacts: A. Sudradjat, VSI; D. Haller, M. Matson, and J. Paquette, NOAA; W. Smith, FAA; M. Krafft, Cernay; Sinar Harapan, Jakarta.