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Report on Lokon-Empung (Indonesia) — May 2003


Bulletin of the Global Volcanism Network, vol. 28, no. 5 (May 2003)
Managing Editor: Edward Venzke.

Lokon-Empung (Indonesia) Increased explosive activity during January-April 2003; local ashfall

Please cite this report as:

Global Volcanism Program, 2003. Report on Lokon-Empung (Indonesia) (Venzke, E., ed.). Bulletin of the Global Volcanism Network, 28:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200305-266100



1.358°N, 124.792°E; summit elev. 1580 m

All times are local (unless otherwise noted)

During 6 January-4 May 2003, higher-than-normal activity was dominated by deep and shallow volcanic earthquakes (table 5), along with gas-and-ash emissions. Several explosions occurred during a period of increased activity in late January-early April. Throughout the report period, a "white-thick ash" emission rose 25-500 m above Tompaluan crater. The Volcanological Survey of Indonesia (VSI) issued a special report during 1-13 February 2003 that described activity in 2002 and early 2003 leading up to the recent increase in activity (table 6).

Table 5. Seismicity at Lokon during 6 January-4 May 2003. Courtesy VSI.

Date Deep volcanic (A-type) Shallow volcanic (B-type) Emission Tectonic Explosion
06 Jan-12 Jan 2003 1 6 10 13 --
13 Jan-19 Jan 2003 1 3 -- 20 --
20 Jan-26 Jan 2003 8 6 4 23 --
27 Jan-02 Feb 2003 6 4 31 11 --
03 Feb-09 Feb 2003 239 763 4 9 --
10 Feb-16 Feb 2003 32 23 7 14 4
17 Feb-23 Feb 2003 239 763 4 9 1
24 Feb-02 Mar 2003 97 353 52 19 12
03 Mar-09 Mar 2003 -- 3 185 6 2
10 Mar-16 Mar 2003 -- -- 90 14 --
17 Mar-23 Mar 2003 2 4 38 17 --
24 Mar-30 Mar 2003 49 335 33 7 1
31 Mar-06 Apr 2003 7 130 5 18 1
07 Apr-13 Apr 2003 4 15 86 17 --
14 Apr-20 Apr 2003 44 285 -- 17 --
21 Apr-27 Apr 2003 46 98 -- 14 --
28 Apr-04 May 2003 25 71 -- 24 --

Table 6. Summary of a special report of activity at Lokon during 2002-2003. Courtesy VSI.

Date Event
09 Feb 2002 An explosion ejected ash to ~ 1,000 m above the crater. Ash fell on Kakaskasen, Telete, and Rurukan villages in the Tondano District in thicknesses of 0.5-2 cm.
10 Apr 2002 At 2302 volcanic earthquakes began to increase, reaching a total of 184 events. An explosion at the same time ejected ash to ~ 1,000 m and glowing material to 250 m above the crater. Ash fell on some villages in thicknesses of 1-3 mm.
12 Apr 2002 At 1816 an explosion ejected ash to 800 m and glowing material to 150 m. Ash drifted S and fell around Kayawu village.
23 Dec 2002 At 0532 an explosion at Tompaluan crater produced an 800-m-high ash column. Ash drifted S and fell around the edifice. Before the explosion, an increase in seismicity (130 volcanic earthquakes in less than 12 hours) was noted.
03 Feb 2003 Volcanic earthquakes began to increase, with a total of 255 events occurring through 7 February.
08 Feb 2003 Tremor was followed by an explosion at 0443 that ejected ash to 1,400 m above the crater. The ash drifted S and was accompanied by glowing material. Ash fell around Taratara, Waloan, and Kayawu villages, at thicknesses of 0.5-1 cm.
10 Feb 2003 After two days repose, at 2219 an explosion occurred. The height of the ash column could not be observed due to heavy rain near the summit. The explosion was preceded by a booming sound. Based on seismograph recordings, the explosion was of medium-high intensity. Explosion earthquakes stopped at 2335. A phreatic eruption at 1406 lasted for 8 minutes.
12 Feb 2003 A significant increase in volcanic earthquakes, mainly during 0100-1000. An explosion at 1408 was followed by a larger explosion at 1102 (based on seismic data; visual observation obscured by thick fog). At 1133 the explosion diminished. At 1225 continuous tremor began with amplitudes of 13-55 mm that continued until 0046 on 13 February.

On 25 January, there was a felt shock (I on the MMI scale). During late January, ash emissions from the crater thickened and emission earthquakes increased. On 3 February the number of deep volcanic earthquakes began to increase at 0600; by 1000, 35 had occurred.

Ash emissions continued to thicken and deep and shallow volcanic earthquakes increased during early February. Emission earthquakes also increased, indicating some low ash explosions. On 8 February at 0443 an explosion ejected ash and glowing material. A booming sound was heard for 30 seconds. A dense ash cloud reached 1,400 m above the crater. Ash fell over the S part of the crater and around Kayau, Tara-tara I and II, and Woloan II and III villages. Ashfall reached thicknesses of 0.5-1 mm. The Alert Level was increased from 2 to 3 (on a scale of 1-4).

Explosions occurred on 10 February at 1405 and 2219. The maximum amplitude of the explosion earthquakes was 50 mm. The height of the ash column could not be observed due to heavy rain. Explosion activity continued on 12 and 16 February. VSI reported that the Alert Level was increased to 4 on 12 February at 0800. From that time through 1100 on 12 February, shallow volcanic earthquakes increased to a total of 164. An explosion followed at 1102, but the ash column could not be observed due to heavy rain. Tremor was recorded beginning on 13 February with amplitudes of 0.5-38 mm.

VSI reported that during 18-20 February, there were 16 explosions and a "white-gray ash" column rose 500 m. An explosion on 22 February was preceded by a swarm of 224 shallow volcanic earthquakes. On 21 February, 29 deep volcanic earthquakes occurred. Within two days, the number of volcanic earthquakes decreased gradually and ended with a large explosion on 23 February at 1034. The explosion was accompanied by thundering and a booming sound, and a "thick-gray ash" column reached 2,500 m above the crater. Ash drifted toward the SE. Tremor (with an amplitude of 1-20 mm) began soon after the explosion. Lokon was at Alert Level 3 during 17-23 February.

During 24 February-2 March, 12 explosions occurred and a "white-gray ash" column rose 300 m. An explosion on 2 March at 2129 was accompanied by glowing material that fell within the crater. A dark gray ash column rose 1,500 m above the crater and ash fell toward the Tondano area (~14.5 km from the crater) with a thickness of ~1 mm. Tremor (with amplitudes of 0.5-25 mm) began soon after the explosion. The explosion had been preceded by a swarm of 204 shallow volcanic earthquakes. A total of 77 deep volcanic earthquakes occurred during 26 February-1 March 2003. Following the 2 March explosion, there were 2 medium-intensity explosions that produced a ~600-m-high "white-gray ash" column.

Ash explosions and emission earthquakes ended on 14 March. On 24 March, the Alert Level was lowered to 2. Normal activity continued, comprised mainly of "white-thick ash" emissions from Tompaluan crater that reached up to 300 m. Tremor continued with amplitudes of 0.5-12 mm.

On 27 March at 0156, an explosion produced a 1,500-m-high ash column that was accompanied by glowing material. Booming and blasting sounds were heard. Ash drifted S and some fell around the edifice, while glowing material reached 400 m high before falling around the crater. Activity was low after the explosion. Tremor continued with amplitudes of 0.5-24 mm.

Following another explosion on 1 April, activity at Lokon decreased. A "white-thick ash" plume continued to rise 100-450 m above the crater. Seismicity was dominated by tremor with amplitudes of 0.5-25 mm. Shallow volcanic earthquakes increased on 15 April to 106 events. Through 20 April, the daily number of shallow volcanic earthquakes fluctuated between 23 and 56 events, but there were no explosions. Activity remained low, but above normal, through at least 4 May.

Geological Summary. The Lokong-Empung volcanic complex, rising above the plain of Tondano in North Sulawesi, includes four peaks and an active crater. Lokon, the highest peak, has a flat craterless top. The morphologically younger Empung cone 2 km NE has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century. A ridge extending 3 km WNW from Lokon includes the Tatawiran and Tetempangan peaks. All eruptions since 1829 have originated from Tompaluan, a 150 x 250 m crater in the saddle between Lokon and Empung. These eruptions have primarily produced small-to-moderate ash plumes that sometimes damaged croplands and houses, but lava-dome growth and pyroclastic flows have also occurred.

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