Bamus is a stratovolcano with four Holocene eruptions: 345 BC, 270 BC, 1645 AD, and 1886 AD. All eruptions were explosive and generated pyroclastic flows.
The summit contains a breached crater filled with a lava dome. A satellitic cone is located on the southern flank, and a prominent 1.5-km-wide crater with two small adjacent cones is situated halfway up the SE flank. Lava's are andesitic.