CVGHM reported increased seismic activity at Sundoro during October -4 December. On 26 November and 2 December smoke was reported from many fumaroles around the summit crater. Based on visual and seismic data, CVGHM raised the Alert Level from 1 to 2 (on a scale of 1-4) on 5 December.

Geological Summary. Gunung Sundoro, one Java's most symmetrical volcanoes, is between the Dieng complex to the NW and Sumbing volcano to the SE. The large Kembang cone is about 2.5 km from teh summit on the SW flank. A small lava dome occupies the summit crater, and numerous phreatic explosion vents are present in the summit area. Lava flows extend in all directions from the summit crater. Deposits of a large prehistoric debris avalanche are located below the NE flank. Pyroclastic-flow deposits dated at 1,720 years before present extend as far as 13 km from the summit. Historical eruptions typically have consisted of mild-to-moderate phreatic explosions, mostly from the summit crater. Flank vents were also active in 1882 and 1903.

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