The 2-km-wide North Island in Lake Turkana is the northernmost and smallest of three volcanic islands in the lake. It is primarily composed of trachyandesitic-to-trachytic phreatomagmatic deposits from overlapping eroded tuff cones or tuff rings. The center of the island consists of a young tuff ring about 1 km in diameter nested inside an older tuff ring. Two fresh unvegetated lava flows that reach the lake shore from the central tuff ring form lava deltas on the N and W sides of the island; the northern delta is about 900 m wide. The two blocky lava flows are younger than a terrace that formed less than 10,000 years ago during the last major high-water level (Key and Watkins, 1988). Geothermal activity occurs along a curvilinear ridge on the S portion of the island and on wave-cut platforms and beaches on the SW shoreline.