Trou au Natron probably formed through two or three separate phreatic eruptions that deposited large blocks around the crater, while an alternative proposal that considers it a collapse caldera appears to not be consistent with field evidence. It formed after the pre-Toussidé caldera considering that its caldera rim is cut by Trou au Natron, at a time where part of the Toussidé volcano already existed, but before the Würm glaciation. Doon Kidimi on the other hand may have formed during the Neolithic Subpluvial, and after Trou au Natron.