Indonesian volcanism is related to the subduction (Benioff) zones of the Indo-Australian and the Pacific-Phillipine plates at the contact with the Asian plate. Rows at volcanoes perpendicular to the plate movement point to steepening of the subduction zone with time. Strato volcanoes and also ignimbrite plateaus associated with socalled “volcano-tectonic” depresssions of deep-seated faults are major features. Fluvio-volcanic flows and slopes are common due to the humid tropical climate. Large volcanic landslides and debris flows causing rupture of crater or caldera rims and the collapse of slopes also are important volcanic geomorphological features. The role of geomorphological survey and the use of aerospace technology in volcanic hazard zoning is emphasized.