The Trou au Natron

Doon Orei — 'the great hole' in Toubou — is one of Africa's most spectacular calderas. Eight kilometres across, a thousand metres from rim to floor, and a bed carpeted in natron, the white sodium carbonate that gives the crater its look of a frozen lake.

Four black scoria cones pierce that white surface, witnesses to late eruptive activity. Fumaroles are still active on the flanks. The descent to the floor, long and exposed, follows a scree gully.