The range includes five shield volcanoes whose diameter can reach , with broad bases and the steepest peaks topped with large craters: Emi Koussi; Tarso Toon, which rises above sea level; Tarso Voon; Tarso Yega; and Tarso Toussidé, which culminates in the peak of the same name. Tarso Yega has the largest crater, with a diameter of and a depth of approximately , while Tarso Voon has the deepest crater, with a depth of approximately and a diameter of . They are complemented by four large lava dome complexes, high and several km wide, all located in the central part of the mountain range: Tarso Tieroko; Ehi Yéy; Ehi Mousgou; and Tarso Abeki, which rises to above sea level. These volcanic complexes are now considered inactive, but according to the Smithsonian Institution were active during the Holocene. Tarso Toussidé is an active volcano that has spewed lava over the past two millennia. Gases escaping from fumaroles on Toussidé are visible when evaporation is low. The volcano's crater, Trou au Natron, is in diameter and deep. On the northwest side of Tarso Voon is the Soborom geothermal field, which contains mud pools and fumaroles that vent sulfuric acid. Sulfur and iron have stained the soil bright colors. Fumaroles are also present at the Yi Yerra hot springs on Emi Koussi. Tarso Tôh was an active volcano in the early Holocene. The volcanic area of the Tibesti Mountains is located entirely in Chad; it covers about a third of the total area of the Tibesti Mountains and is responsible for between of rock.