From Wikipedia: https://en.wikipedia.org/wiki/Crater_Highlands

The Crater Highlands (Ngorongoro Highlands) are a region along the East African Rift in Tanzania, located in a spreading zone at the intersection of branches of the African and Somali tectonic plates, resulting in distinctive and prominent landforms.

The highlands are named for the many craters and calderas present. As common in spreading zones, volcanoes can be found here. Magma, rising to fill the gaps, reaches the surface and builds cones. Calderas form if a volcano explodes or collapses, following the emptying of the magma chamber below, and further spreading can fracture the volcanoes as well.