A white, low-density plume rose 50-200 m above Lokon's summit during 2-8 January 2001. Seismographs recorded a high number (~250) of both deep and shallow volcanic earthquakes during the week. The following week a plume continued to rise, and volcanic earthquakes decreased in number by about 90%. Discontinuous tremor with amplitudes of 0.5-6.0 mm was registered. During 16-22 January the plume rose up to 250 m in height. Volcanic earthquake activity again spiked, but reached only about half the quantity that had occurred during the first week of the month. Discontinuous tremor continued having amplitudes of 0.5-2.6 mm.

An explosion sent ash and glowing ejecta skyward from Lokon at 1920 on 28 January. Explosion earthquakes registered a maximum amplitude of 48 mm during a 175-second interval. Volcanic bombs were ejected from the crater and fell on Lokon's N slope. The ash cloud's specifics could not be measured due to rainy weather. Workers at the Kakaskasen observatory post detected an acrid sulfurous smell following the explosion. Observations the following day, 29 January, revealed a light-colored, high-density ash plume that rose ~300 m. The hazard status for Lokon was raised from 2 to 3 (on a scale of 1-4) following the explosion. Early February activity showed a decrease in unrest, although a high-density plume continued to rise up to 350 m, and small explosion earthquakes with amplitudes of 20-30 mm recurred.

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