Suswa

The phonolitic-to-trachytic Suswa volcano in the Kenyan Rift, ~50 km WNW of Nairobi, is notable for its 8 x 12 km caldera. Construction of an early shield volcano was followed by eruption of voluminous Pleistocene pumice and lava flows that accompanied incremental formation of the caldera. The post-caldera lava cone of Ol Doinyo Onyoke ("The Red Mountain," also known as Ol Doinyo Nyukie) is on the south side of the caldera. A large elongated summit crater is truncated on the north by a ring graben. This unusual 5-km-wide circular graben at the center of the older caldera isolates a tilted island block of caldera-floor lava flows. Some lava flows from flank vents remain unvegetated and may be only a century or so old, but have not been dated.