Lokon Volcano

A small town of Kakaskasen, Tomohon City just located of about 4 - 5 km eastern part of the Lokon active crater. Lokon is one of the most active volcanoes in Indonesia, located at 1.21ºN and 124.47ºE in Tomohon City,

Minahasa Regency, North Sulawesi, Indonesia. Lokon, the higher of the two peaks ( whose summits are only 2.2 km apart), has a flat, craterless top. The morphologically younger Empung volcano has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century, but all subsequent eruptions have originated from Tompaluan, a 150 x 250 m wide double crater situated in the saddle between the two peaks.

The historical interval periods of activities typically have periods 1 – 4 years with dormant intervals of 8 – 64 years. The activity of Lokon Volcano was initiated by ash/gas explosion and followed by magmatic eruptions. Sometimes the activities were accompanied by pyroclastic flows. In normal condition, the Lokon activity is solfatara/fumarole stage. The maksimum height of the white cloud was about 150 m above crater rim of Tompaluan.

The increasing of seismic activity began at June 2007, during June - November 2007 recorded 10 A-type and 15 B-type earthquakes per day, and no tremor. From December 7^th 2007, the number of volcanic earthquake increasing rapidly, 21 A-type and 46 B-type, and the tremor vulcanic start appear. December 8^th 2007 recorded 35 A-type and 55 B-type volcanic earthquake and tremor volcanic recorded continuously. Tiltmeter data during 2007 showed the inflation pattern around the crater for +5 microradion both tangential and radial component.

On 9 December 2007, CVGHM raised the Alert Level for Lokon-Empung from 2 to 3 (on a scale of 1-4) based on visual observations, inflation detected by deformation instruments, and an increase in seismicity. The water in the Tompaluan crater changed color from green to gray and noises from degassing became stronger.

Herewith the eruptive hystory of Lokon Volcano:

1991	12 January, 6, 28 March, Ash explosion 10 - 11, 17 May, Gas emissions to 450 m height were observed during the morning and afternoon of 10 May. One week later (17-18 May), ash was erupted to 200-400 m height. Seismicity then decreased, with one deep and three shallow volcanic earthquakes recorded during the last week of May, down from six deep and nine shallow events the second week of the month. 26 - 28 May, Ash explosions occurred at 15.37 WITA on 27 May and 1000 on 28 May, producing columns 250 m high 1 - 30 June, 4 - 7. 9. 11 July, Ash explosions. Seismic activity was characterized by explosion earthquakes, averaging 30-50 recorded events/week. Shallow and deep volcanic earthquakes were less frequent (2-8 and 3-9 events/week, respectively). Tectonic earthquakes ranged from 18 to 101 weekly. 19 September, 24 October, ejected a plume to ~700 m and lava dome growth 24, 25 October, Vigorous explosions on 24 October ejected ash to ~2 km height, and may have generated a pyroclastic flow on 25 October that slid down to Pasahapen River 1000 m from eruption center. 26 - 31 October, 1, 6, 12, 17, 20, 24 November, 1 December, explosion. Ash and incandescent material ejected on 6 November reached 300 m height. Large explosions on 17 and 20 November produced ash columns 1,000 and 2,500 m high. The recorded explosion, on 1 December at 17.17 WITA, was preceded by tremor that morning and the previous day. The press described an apparently unrecorded ash emission episode that produced a 300 m plume during the morning of 11 December. Gas rose to 200-300 m height between explosions. The eruption ended in January 1992. The 1991 explosion formed lava plug in the bottom of crater
1993	April, increasing seismicity, continous tremor recorded. June - September, increasing seismicity, swarm volcanic recorded
1997	12 December, phreatic eruption in the bottom of crater and produce a hole with diameter 5 m.
2000	Visual and seismic activity increased notably in mid-March, and the alert level for Lokon-Empung was set at 2 on a scale of 1-4. A very dense gas emission caused vegetation on the eastern slope to wither. During this period, 45 deep volcanic (A-type) earthquakes, 210 shallow volcanic (B-type) earthquakes, and 12 tectonic earthquakes occurred. Tompaluan crater emitted white medium-dense gas that rose 50-150 m above the crater rim in late March. Seismicity changed, with fewer volcanic and more tectonic earthquakes than in the previous weeks. At the beginning of April, the number of A-type earthquakes increased, but visual activity remained similar to the previous week. 7 July, observed cracking and a new hole (red hole and lightening), with diameter 7 m in the bottom of crater. Activity remained similar during 31 July-7 August. White variably dense ash clouds continued to rise to heights of up to 300 m, and lava fountaining up to 25 m above Tompaluan crater was visible during the first week of August. Tectonic earthquakes became dominant, and the amplitude of volcanic tremor reached 0.5 mm. Ash plumes rose to 500 m above the crater rim, and lava fountaining persisted in mid-August. Continuous tremor had amplitudes of 0.5-1 mm. The ash plumes decreased in height to 300 m above the crater the following week. The number of volcanic earthquakes increased slightly, and tremor decreased in amplitude to 0.5 mm. Activity increased slightly in September. The ash plume reached progressively higher, ranging from 50 m to 350 m and eventually up to 400 m. Continuous tremor amplitude increased to 0.5-1 mm. Few volcanic earthquakes occurred, so tectonic earthquakes were dominant. The alert level for Lokon-Empung was decreased from 3 to 2 in early October, and activity decreased during the month. The white variably dense ash plume decreased in height to 250 m, although lava fountaining remained visible at a consistent height of 25 m. Seismicity also decreased, and tremor ceased by the end of October.
2001	28 January pukul 19.20 WITA, Explosions produced incandescent material (volcanic bomb) that fall around the Tompaluan crater. 26 March, at 14.40 WITA an eruption sent a dark ash plume 1,500 m above the crater rim that drifted E and N. No incandescent material was observed, but 25 minutes after the explosion ash started to fall at Kinilow and Kakaskasen villages (3.5 and 4 km from the crater, respectively). Activity slowly decreased though 15.10 WITA, when thick white gas emissions rose 400 m above the crater. The ashfall was 0.3-0.5 cm thick at Kinilow, 0.1-0.3 cm thick at Kakaskasen, and 1-2 cm thick around the Pasahapen River ~1 km from the crater. After the initial explosion, volcanic tremor recorded between 14.42 and 14.57 WITA had a maximum amplitude of 2-16 mm. 20 May at 20.14 WITA ejecting glowing material that rose as high as 400 m and then fell around the crater. The explosion produced a gray-black plume that rose to 900 m and drifted North. The explosion produced incandescent material reached 400 m and felt around the crater. The eastern of lava plug that formed after 1991 explosion was up lifted
2002	9 February 2002 , Plumes rose to 1.0 km and moved toward the SE, depositing ash (~0.5-2 mm thick) around the villages of Kakaskasen III, Talete I, Talete II, and Rurukan. The phreatic eruption was triggered by extensive rainfall; specifically, 602 mm of rain fell during January 2002 compared to 193 mm during December 2001. This excessive rainfall was thought to cause instability of the edifice. After the eruption, activity decreased significantly and remained low through at least February 2002 26 March at 14.40 WITA, Lokon exploded again, producing dark ash that rose 1.5 km above the crater rim and drifted E and N. The explosion did not produce any incandescent material. Ash began falling on Kinilow (3.5 km from the crater) and Kakaskasen villages (4 km from the crater) 25 minutes later, eventually reaching a thickness of 1-2 cm near Pasahapen river (~1 km away). Tremor shortly after the explosion had a maximum amplitude of 2-16 mm. 10 Apr 02 at 23.02 WITA 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 02 at 18.16 WITA an explosion ejected ash to 800 m and glowing material to 150 m. Ash drifted S and fell around Kayawu village. On 23 December at 05.32 WITA 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.
2003	8 Feb 03, Tremor was followed by an explosion at 04.43 WITA 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 03 After two days repose, at 22.19 WITA 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 23.35 WITA. A phreatic eruption at 14.06 WITA lasted for 8 minutes. 12 Feb 03 An explosion at 14.08 WITA was followed by a larger explosion at 11.02 WITA (based on seismic data; visual observation obscured by thick fog). At 11.33 WITA the explosion diminished. At 12.25 WITA continuous tremor began with amplitudes of 13-55 mm that continued until 00.46 WITA on 13 February. On 27 March at 01.56 WITA, 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. On 1 April, following another explosion 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