The O'a Caldera, also known as Shala, is a volcanic

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

Ethiopia Ethiopia, officially the Federal Democratic Republic of Ethiopia, is a landlocked country located in the Horn of Africa region of East Africa. It shares borders with Eritrea to the north, Djibouti to the northeast, Somalia to the east, Ken ...

. It has two lakes:

Lake Shala Lake Shala (also spelled Shalla) is an alkaline lake located in the Ethiopian Rift Valley, in the Abijatta-Shalla National Park. Overview The lake is 28 kilometers long and 12 wide,''Statistical Abstract of Ethiopia for 1967/68'' with a surfa ...

and a small

maar A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallow ...

called Lake Chitu. Sub-features include Mount Fike (a pyroclastic cone) and Mount Billa (a cinder cone).

References

Volcanoes of Ethiopia Calderas of Ethiopia Rift volcanoes VEI-7 volcanoes {{Ethiopia-geo-stub