Report on Lewotobi (Indonesia) — June 2003
Bulletin of the Global Volcanism Network, vol. 28, no. 6 (June 2003)
Managing Editor: Edward Venzke.
Lewotobi (Indonesia) Minor explosion and ashfall on 30 May
Please cite this report as:
Global Volcanism Program, 2003. Report on Lewotobi (Indonesia) (Venzke, E., ed.). Bulletin of the Global Volcanism Network, 28:6. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200306-264180
Lewotobi
Indonesia
8.542°S, 122.775°E; summit elev. 1703 m
All times are local (unless otherwise noted)
An explosion on 12 October 2002 at Lewotobi Lakilaki, one of the twin stratovolcanoes that comprise Lewotobi, produced an ash column that rose ~500 m above the volcano (BGVN 27:11). Through at least 24 November, a "thin white low-pressure ash plume" rose 150-250 m above the summit.
No further reports were issued until May 2003, when the Volcanological Survey of Indonesia reported an explosion at 1650 on 30 May 2003. The resulting ash column reached 200 m above the summit and caused ashfall at the observatory, ~5 km from the crater. Visual and seismic data showed no significant increases during the week prior to the explosion (table 1). On 1 June, two explosion earthquakes and two tremor earthquakes were recorded. The hazard status was set at Alert Level 2 (on a scale of 1-4).
Table 1. Seismicity and height of the gas plume at Lewotobi during 20 May-15 June 2003. Courtesy VSI.
| Date | Volcanic EQ | Tectonic EQ | Ash Emissions | Tremor | Plume Height(s) |
| 20 May 2003 | 2 | 1 | -- | -- | 25 m |
| 21 May 2003 | 0 | 0 | -- | -- | -- |
| 22 May 2003 | 4 | 1 | -- | -- | 25 m |
| 23 May 2003 | 9 | 5 | -- | -- | 25 m |
| 24 May 2003 | 6 | 3 | -- | -- | 25 m |
| 25 May 2003 | 5 | 1 | -- | -- | 25 m |
| 26 May 2003 | 0 | 0 | -- | -- | 25 m |
| 27 May 2003 | 2 | 6 | -- | -- | 25 m |
| 28 May 2003 | 0 | 2 | -- | -- | -- |
| 29 May 2003 | 2 | 0 | -- | -- | -- |
| 30 May 2003 | 6 | 3 | -- | -- | 200 m |
| 31 May 2003 | 6 | 0 | -- | -- | -- |
| 01 Jun 2003 | 3 | 1 | -- | -- | -- |
| 02-08 Jun 2003 | 13 | 12 | 29 | 20 | 300 m |
| 09-15 Jun 2003 | 24 | 9 | 40 | 33 | 75 m |
Activity during the week of 2-8 June 2003 was marked by explosions and ash emissions. Ash plumes reached a maximum height of 300 m above the summit. Seven explosions were recorded accompanied by a blasting sound on 3, 5, and 6 June. Ash fell at Bawalatang, Duang, and Boru villages. Shallow volcanic earthquakes were recorded, but were fewer in number compared to the previous week; there was no record of deep volcanic earthquakes, although tectonic earthquakes were recorded.
During the week of 9-15 June, activity was marked by ash emissions, with an ash plume reaching a maximum height of 75 m above the summit. Tremor events were also observed, with the tremor showing an amplitude of 0.5-7 mm. There were no deep volcanic earthquakes recorded, although the numbers of shallow volcanic earthquakes, tremor and ash emissions increased.
Geological Summary. The Lewotobi edifice in eastern Flores Island is composed of the two adjacent Lewotobi Laki-laki and Lewotobi Perempuan stratovolcanoes (the "husband and wife"). Their summits are less than 2 km apart along a NW-SE line. The conical Laki-laki to the NW has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has had observed eruptions in 1921 and 1935. Small lava domes have grown during the 20th century in both of the summit craters, which are open to the north. A prominent cone, Iliwokar, occurs on the E flank of Perampuan.
Information Contacts: Dali Ahmad, Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).
