In a special report for the Dieng Volcanic Complex issued on 4 June the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) noted that carbon dioxide gas concentrations at Timbang Crater began to increase on 29 May. Seismicity did not increase. The Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay 500 m away from Sileri Crater, to not approach Timbang Crater, and to be vigilant when digging in the area due to risks of carbon dioxide gas exposure.

Geological Summary. The Dieng plateau in the highlands of central Java is renowned both for the variety of its volcanic scenery and as a sacred area housing Java's oldest Hindu temples, dating back to the 9th century CE. The Dieng Volcanic Complex consists of multiple stratovolcanoes and more than 20 small Pleistocene-to-Holocene craters and cones over a 6 x 14 km area. Prahu stratovolcano was truncated by a large Pleistocene caldera, which was subsequently filled by a series of cones, lava domes, and craters, many containing lakes. Lava flows cover much of the plateau, but observed activity has been restricted to minor phreatic eruptions. Gas emissions are a hazard at several craters and have caused fatalities. There are abundant thermal features and high heat flow across the area.

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