Since the end of the vigorous activity that began on 24 October, 16 explosions from the active Tompaluan Crater have been recorded (figure 2). Ash column heights ranged from 200 m to >250 m above the rim of Tompaluan . . . . The most recent recorded explosion, on 1 December at 1717, 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. Local seismicity continued at somewhat reduced rates (figure 3).

Figure 2. Number of recorded explosions/day at Lokon-Empung, 24 October-12 December 1991. Courtesy of VSI.

Figure 3. Number of recorded earthquakes at Lokon-Empung, 28 October-12 December 1991. For each day, three bars are shown, distinguishing shallow volcanic earthquakes (left), deep volcanic shocks (center), and tectonic events (right). Arrows indicate tremor episodes. Courtesy of VSI.

VSI warned that additional explosions were still anticipated, and the area designated by their 1986 hazard map remained at risk. The press reported that [~10,000] people had fled the 24 October activity, but most had returned home by early December.

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: VSI; UPI.