Lake Naivasha and the Mount Longonot and Hell’s Gate National Parks

Abstract

Lake Naivasha , is the highest of the rift valley lakes in Kenya, occurring at an altitude of 1,884 m. The lake is rimmed by substantial swamps and the average depth of 6 m is highly variable. Two active volcanic systems, Mount Longonot and the Olkaria Volcanic complex occur on the southern shores. The Longonot Volcano includes a prominent cone (2,776 m) with a well-defined summit crater; the most recent eruption was in 1860. The cone is located within a much larger caldera; multiple caldera events triggered huge outpourings of lavas and ignimbrites in the period 21,000–6,000 BP. The volcanism at Longonot is dominated by trachytic basalt lavas with abundant pyroclastic deposits. The geology of the Hell’s Gate National Park, named from the lunar landscapes in a valley fringed by lava cliffs, is dominated by sections of the Olkaria Volcanic complex. This last erupted approximately two hundred years ago. The Njorowa Gorge , a narrow slot rimmed in by near-vertical sidewalls, exposes a section of finely bedded ashes which accumulated from explosive eruptions of rhyolitic magmas. The gorge formed when the much larger, palaeo-Lake Naivasha drained southwards during the Late Pleistocene–Early Holocene. Many of the eruptions at Olkaria occurred beneath this palaeo-lake. Olkaria is an important source of obsidian or volcanic glass, used by ancient cultures for stone tools. The Mount Longonot Volcano and the Olkaria Volcanic complex are both potentially hazardous and should be carefully monitored, particularly, as they occur proximal to the relatively densely populated area around Lake Naivasha . The style of volcanism at Olkaria can be compared with the Yellowstone Volcano in Wyoming, potentially one of the most destructive volcanoes on Earth. The shallow magma chamber at Olkaria is a major source of geothermal energy that provides much of Kenya’s electricity.

Photographs not otherwise referenced are by the author.