North Island is a collection of several tuff cones in the northern part of Lake Turkana. The lake was previously referred to as "Lake Rudolf," and in 1975, the name was changed to "Lake Turkana." The island is 1.24 miles (2 km) across. It is about 722 ft (220 m) high, 459 ft (140 m) of which is above water. Phreatomagmatic material makes up North Island. The cones are made of lapilli, tuffs and thin basalt flows. A young tuff ring about one km around is in the center of the island. It is inside an older and larger ring. Trachyte lava fills the central ring and flows out on the west side. The same kind of lava is found on the north part of the island too. These lavas are dark brown. North Island is about 3.25 million years old. There is much geothermal activity on the island. This is found along a fault ridge which stretches NE-SW across the island. Many fumaroles and solfataras can also be found on North Island.
Dunkley, P.N., et al, "The geothermal activity and geology of the northern sector of the Kenya Rift Valley," British Geological Survey Research Report SC/93/1, 185 pp., 1993.
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