Remote Analysis and Statistical Identification of Rootless Cone Groups in the Kenya Rift (Kenya)

Abstract

Rootless volcanic cones are found around the world, commonly in areas where lava flows occur in close proximity to sources of water (e.g., Iceland and Hawaii). Often referred to as littoral cones or pseudocraters, rootless cones are produced when basaltic pahoehoe lava flows are emplaced over a wet substrate or into shallow water environments, resulting in small phreatomagmatic eruptions that produce cone features on top of the host lava flow. Rootless cones can be valuable paleoenvironmental indicators as they indicate the presence of water during the emplacement of lava flows and their subsequent formation, even if climate conditions today do not support a wet environment. High-resolution aerial imagery and digital elevation models were used to map volcanic cones within the Baringo-Suguta Trough of the Northern Kenya Rift. The resulting mapped features were then subject to various statistical analyses to determine the volcanic, tectonic, and paleo-environmental processes responsible for their formation. Three distinct types of volcanic centres were observed in the Baringo-Suguta Trough. The volcanic edifices identified are typical of the Kenya Rift and include large silicic caldera complexes that occur consistently along the length of the rift and smaller, typically mafic cones recognized here as dikefed structures. The alignment trends of dike-fed volcanic cones are rift parallel. However, smaller examples clustered around the Emuruangogolak Caldera produce alignments oblique to the rift, suggesting localized strain variations resulting from pre-existing structures. A third group of comparatively smaller and closely spaced cones were observed and confidently identified as rootless cones based on similarities to other, more widely studied rootless cone groups in Iceland. The rootless cones within the Baringo-Suguta Trough are hosted by a lava flow sourced from the nearby Emuruangogolak Caldera. The elevation of the cone group and proximity to the paleo- Northern River suggests that the lava flow was emplaced during the African Humid Period ~13.9 – 6.7 ka when the local climate was much wetter, and interconnected lakes and river systems dominated the rift valleys. Thus, this study reveals that in arid or semi-arid environments of the Kenyan Rift, the presence of rootless cones can be used to infer the extent of local water tables during past climate variations and potentially assist in constraining the emplacement age of the flows based on past water availability.