The southernmost and largest of the three volcanic islands in Lake Turkana, South Island (sometimes referred to as Hohnel Island), contains numerous tuff cones. Early stage cone formation may have been associated with a high stand of Lake Turkana dated at about 10,000 years ago, and later subaerial activity postdates the last high stand of the lake about 3,200 years ago. The island is within a volcanic horst that extends 10 km to the N beneath the lake surface. Dominantly basaltic lava flows erupted from a N-S fissure extending the 11-km length of the island are morphologically similar to Holocene flows from The Barrier volcano at the S end of Lake Turkana. An eruption from a scoria cone on the island was witnessed during Count von Teliki's 1888 expedition.