An increase in the number of volcanic earthquakes at Tongkoko since 24 October led VSI to raise the Alert Level from 1 to 2. The number of deep volcanic earthquakes decreased in comparison to the previous week. VSI reported that the increased number of shallow volcanic earthquakes indicated that seismicity was migrating to the surface.

Geological Summary. The eastern peninsula at the far NE end of Sulawesi near the city of Bitung is occupied by a volcanic complex consisting of two major edifices within a nature reserve. To the north is Tangkoko (also known as Tongkoko), with a large caldera (~3 x 1.5 km) elongated towards the SE from the highest rim point; the rim at the opposite end is more than 400 m lower. Eruptions occurred from the summit crater in the 17th century and in 1801, when the caldera also reportedly contained a cone surrounded by a lake. About 1.5 km down the outer E flank is the Batuangus (or Batu Angus) lava dome, formed in 1801, along with an adjacent vent (Baru Batuangus) that has been the source of all subsequent eruptions. The higher twin-peaked Duasudara (also Dua Suadara) stratovolcano is about 4.5 km SW of the Tangkoko summit. A NE-facing open crater appears to have a hummocky debris flow that reaches the base of the Tangkoko edifice.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)