Description/Abstract Kawah Ijen volcano on the eastern tip of Java, Indonesia, has recently been classified as the second most dangerous volcano in the Sunda-Banda volcanic arc. It gained this status for its crater lake, which represents the largest natural body of hot, hyperacid brine in the world, combined with its location next to a large population centre. In addition, it presents major challenges to eruption forecasting as a result of a lack of historical data and modification of seismic warning signals by the hydrothermal system and crater lake. In this talk, I will present how we have used a broad understanding of the internal plumbing of the Kawah Ijen magmatic-hydrothermal system to identify the chemical indicators of volcanic unrest, and how we have used the mineral record to establish warning levels for these indicators.