Article thumbnail

Mount Kenya volcanic activity and the Late Cenozoic landscape reorganisation in the upper Tana fluvial system

By A. Veldkamp, J.M. Schoorl, J.R. Wijbrans and L.F.G. Claessens

Abstract

Volcanic–fluvial landscape interaction of the late Cenozoic Mt Kenya region in the upper Tana catchment has been reconstructed. The oldest newly dated phonolite flow is 5.78 Ma (40Ar/39Ar), placing the initiation of Mt Kenya volcanic activity within the Late Miocene, much earlier than reported before, 3–3.5 Ma (K/Ar). The main body of the stratovolcano was already in existence around 4.22–5.27 Ma (40Ar/39Ar) supplying lahars to its lower footslopes. The final recorded volcanic main vent phase in the study area produced multiple phonolitic flows and lahars around 2.8 Ma (40Ar/39Ar). There is evidence of at least two major Pliocene drainage blocking events between 3.89 and 2.81 Ma (40Ar/39Ar) causing lava dammed lakes in which volcanic tuff deposits accumulated. Around this time the river Tana did not incise much and shaped an extensive fluvial plain, whose remnants can now be found around 1150 m altitude. This fluvial plain has been incising during the last 2.8 Ma, whereby the incision rate changed in time due to changing uplift rate and volcanic events. A flood basalt eruption covering 1150 km2, estimated to be 5 km3, on the south flank of Mt Kenya of the Thiba basalts at 0.80 Ma (40Ar/39Ar) plugged the Upper Tana basin and caused significant drainage reorganisation. The Tana was diverted southwards abandoning its former valley. The terrace record in the Tana valley downstream the Thiba basalts appears to register this event as a post 0.8 Ma accelerated incision. Current Thiba valley morphology is relatively young and appears to register uplift controlled terraces with interbedded lahars for the last 300 ka only, indicating a delayed fluvial response of approximately 0.5 Ma. The landscape reconstruction demonstrates that the Tana was well able to compensate for many volcanic events such as lahars and lava flows. Only the build-up of a stratovolcano body and a large flood basalt caused prolonged impact on fluvial landscape developmen

Topics: african climate-change, western turkey, sediment yield, gregory rift, debris flows, east-africa, pleistocene, evolution, river, uplift
Year: 2012
DOI identifier: 10.1016/j.geomorph.2011.10.026
OAI identifier: oai:library.wur.nl:wurpubs/424579
Provided by: Wageningen Yield
Download PDF:
Sorry, we are unable to provide the full text but you may find it at the following location(s):
  • https://library.wur.nl/WebQuer... (external link)
  • Suggested articles


    To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.