O'a Caldera

The Shala (also known as O'a) caldera along the central Main Ethiopian Rift forms the eastern portion of the 15 x 25 km Lake Shala. Formation of the caldera about 240,000 years ago was accompanied by the eruption of two ignimbrite deposits, the first of which was strongly welded. The only post-caldera activity consists of two pyroclastic cones to the N, one silicic and the other basaltic, and a group of tuff rings, spatter cones, and lava flows of Holocene age near the SW shore of the lake. These were erupted along the Corbetti-Shalla segment of the Wonji Fault Belt, which extends N from Corbetti caldera. Fumarolic activity continues on all sides of the lake.