Ijen volcanic complex

Ijen lies in Indonesia's Sunda volcanic arc in eastern Java. The Smithsonian Global Volcanism Program identifies Ijen as a composite volcanic complex and records Kawah Ijen as the intracaldera cone containing a crater lake. The lake is described as an acid brine body roughly 700 by 800 metres across. The complex's volcano profile lists an elevation of 2,769 metres and coordinates of 8.058°S, 114.242°E.

Kawah Ijen's crater lake and hydrothermal system are sites of volcanic activity. Sulfur-bearing gases and deposits are part of the setting. Sulfur has also been extracted by miners working inside the crater: the Smithsonian's Global Volcanism Program describes laborers carrying heavy loads of native sulfur across steep terrain while exposed to volcanic gases. BBC reporting describes the extraction process in which molten sulfur is tapped through pipes, cools into solid sulfur and is carried out by hand.

Ijen's volcanic environment can pose hazards from gas emissions, crater-lake activity and seismic unrest. The Global Volcanism Program relays observations and alert-level information from Indonesia's geological authorities. In its weekly report covering 7–13 August 2024, it reported that the alert level had been lowered to 1 and that visitors, residents and miners were advised not to approach the crater rim, descend into the crater or remain overnight within 500 metres of the rim. Such dated advisories should not be taken as current safety guidance; local authorities' latest notices should be consulted before travel.