PVMBG reported that during 1-17 December the maximum height of steam-and-gas plumes at Raung was 500 m above the summit. An M 2.6 local tectonic earthquake was detected on 18 December and afterwards plumes rose as high as 1 km. Seismicity during December indicated that fluid movement was concentrated at shallow depths; signals indicating emissions significantly increased on 18 December. Deformation data indicated a trend of deflation. On 18 December PVMBG raised the Alert Level to 2 (on a scale of 1-4) noting that the visual observations and seismic data indicated unstable conditions. The pubic was warned to stay 3 km away from the summit crater.

Geological Summary. Raung, one of Java's most active volcanoes, is a massive stratovolcano in easternmost Java that was constructed SW of the rim of Ijen caldera. The unvegetated summit is truncated by a dramatic steep-walled, 2-km-wide caldera that has been the site of frequent historical eruptions. A prehistoric collapse of Gunung Gadung on the W flank produced a large debris avalanche that traveled 79 km, reaching nearly to the Indian Ocean. Raung contains several centers constructed along a NE-SW line, with Gunung Suket and Gunung Gadung stratovolcanoes being located to the NE and W, respectively.

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