Toussidé lies in the Tibesti Mountains, the large Yirrigué caldera and the smaller Trou au Natron and Doon Kidimi craters are close to it.

[8] The towns of Bardai and Zouar lie east-northeast and south of Toussidé, respectively,[3] and a road between the two passes just southeast from Trou au Natron.

[14] In the past it was considered to be lower, only 2,500 metres (8,200 ft), before a higher summit height was determined by Jean Tilho and W.G.

[28] Yirrigué contains a small cinder cone and an associated 1 kilometre (0.62 mi) long lava flow,[29] as well as an alluvial plain.

[27] The "Yirrigué" caldera is part of a large rhyolitic shield-shaped volcano[30] that developed on top of a tectonic horst, which in turn may have been formed by intrusion of magmas.

[34] Inside of Trou au Natron are four[23] recent basaltic volcanic cones,[3] the most remarkable of which is the 75-metre (246 ft) high Moussosomi, which has erupted a lava flow.

[28] Cones are also located outside of the Trou au Natron, and their eruption products have in part flowed into the crater.

[34] Like Toussidé, the position of Trou au Natron appears to be controlled by the ring fault of the "pre-Toussidé" caldera.

[21] A salty swamp lies within Trou au Natron,[35] whose floor is in part covered by evaporites,[20] mainly sodium sulfate.

[41] Later analysis suggested that there was no late Pleistocene lake stage and that Trou au Natron was filled with water between 8,645 calibrated radiocarbon years ago to about 4,425 calibrated radiocarbon years ago, thus at the same time as lakes in the lowland.

[44] The formation of such a lake during the glacial maximum was probably dependent on orographic precipitation transported by the subtropical jet stream.

[39] The Tibesti mountains are part of a volcanic province that reaches from Libya into Chad and covers a total surface area of about 100,000 square kilometres (39,000 sq mi).

Most of it falls as frontal precipitation during summer,[50] and it is more copious than in the lowlands; the Tibesti mountains are the sources for wadis.

It ranges from cyanophyceae, ferns, mosses, Oldenlandia and Selaginella within the fumarole vents to small meadows consisting of mosses and Campanula monodiana, Fimbristylis minutissima, Lavandula antineae, Mollugo nudicaulis, Oxalis corniculata, Satureja biflora[52] and other species.

[22] The plant Erodium toussidanum is endemic at the fumaroles of Toussidé,[54] and the mountain is the type locality of Salvia tibestiensis.

[31] Trou au Natron probably formed through two or three separate phreatic eruptions[16] that deposited large blocks around the crater,[23] while an alternative proposal that considers it a collapse caldera[58] appears to not be consistent with field evidence.

[60] Finally, in Trou au Natron there are hot springs that deposit trona[35] and fumarolic activity has been reported there.