Wonchi contains a single crater lake about 1476 feet (450 meters) below the rim of the volcano.
Passage into the caldera floor is via a narrow gash worn through the caldera rim by a small stream. It is possible that Wonchi was active as recently as A.D. 550. Flooding of the lake at that time may have been due to an underwater eruption that raised the lake level, killing many trees on the previous shore. Wonchi's caldera is as much as 2952 ft (900 meters) deep, and lake itself could be as deep as 1312 ft (400 meters).
Sources of Information:
Smeds, Helmer, "A Note on Recent Volcanic Activity on the Ethiopian Plateau, as Witnessed by a Rise of the Level of Lake Wonchi 1400 +/- 140 B.P.," Acta Geographica, v. 18, n. 1, 32 pp, 1964.
Images of Volcanoes To VolcanoWorld