Dieng is classified as an active volcanic system. Its hazards include phreatic (steam-driven) bursts at craters such as Sileri, sulfur gas emissions, and — most dangerously — releases of carbon dioxide, an odorless gas heavier than air that can accumulate in low-lying areas without warning.
The benchmark event occurred in 1979, when Sinila crater released a CO2 cloud that killed 149 people near Timbang village. Indonesian volcanological authorities monitor the plateau and publish hazard guidance; anyone researching a visit should consult current official advisories, since crater conditions can change quickly.