Climate change is driving wildfires to higher elevations in tropical mountains, exposing ecosystems with little or no fire history. We analyse a 2012 fire in Uganda’s Rwenzori Mountains that burned pristine forest and wetland above 3800 m, where no major fire had occurred for 12,000 years. The fire triggered a long-term cascade of floods, debris flows, landslides, erosion and mine-waste pollution, showing the need for rapid post-fire risk assessment and restoration.