Toussidé itself lies in part within an even larger caldera, the pre-Toussidé (also known as Yirrigué) caldera which is in part filled by the lava flows from Toussidé and eruption products from the more recent explosion craters, as well as debris that fell from the steep caldera margin. Toussidé is located on the caldera's western side, and the smaller Trou au Natron caldera cuts into the flanks of Yirrigué. Yirrigué contains a small cinder cone and an associated long lava flow, as well as an alluvial plain. The Yirrigué caldera is part of a large rhyolitic shield-shaped volcano that developed on top of a tectonic horst, which in turn may have been formed by intrusion of magmas. The ignimbrites have buried older terrain and filled valleys.