During the early Holocene, Era Kohor was filled with a deep, circular lake. Diatom beds have been found above the floor of Era Kohor and in depressions without outlet elsewhere in the caldera, they reach thicknesses of . Farther down on the mountain, gullies start appearing at elevation and become deep gorges by elevation. Elleboe wadi originates on Emi Koussi, and several streams on the western flank join into the Enneri Miski which drains southwards and disappears south of the mountains. Small pools of water are found around Emi Koussi.