CVGHM reported that seismicity at Sundoro continued to increase into January after the Alert Level was raised from 1 to 2 (on a scale of 1-4) on 5 December 2011. After the first week of January through 27 March the number of daily earthquakes significantly decreased. The Alert Level was lowered to 1 on 30 March.

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)