The timescale and process of magma storage and transportation at continental rifts is not well understood. Extension, fault structures and hydrothermal systems all influence magma storage, volcano deformation and volatile emissions at rift volcanoes. This thesis uses a multidisciplinary approach to study these processes within the Kenyan Rift (KR), combining satellite and ground-based observations of deformation, structure and degassing. Using satellite radar (InSAR) , I show diverse deformation histories exhibited by 5 deforming volcanoes, including: coupled magmatic uplift-hydrothermal subsidence; longterm magmatic subsidence; and hydrothermal subsidence. At individual volcanoes, deformation of discrete magma lenses is connected by a crystal-melt mush, and by studying clustered volcanoes; I place geophysical constraints on its lateral extent at 30 x 15 km. A soil CO2 survey at Longonot volcano shows that passive degassing is controlled by volcanic structures. The total CO2 degassing is magmatic in origin and estimated at 10-1 - 102 t d -1; but emissions are likely modified by a hydrothermal system. By extrapolation, I conclude that restless rift volcanoes may emit globally significant quantities of C02 by passive degassing. The northern and southern segments of the KR are found to be in orthogonal and oblique extension respectively. Southern calderas are aligned NE-SW, lying oblique to recent rift faults but aligned with pre-existing rift faults suggesting that pre-existing structures control the location and dimensions of mid-crustal magma reservoirs, whereas smaller cones and vents tend to be aligned along currently active structures. This thesis demonstrates that pre-existing and currently-active structures influence magma storage, transfer and volatile emissions at varying crustal levels and that isolated crystal-melt mush regions likely exist beneath all volcanoes, but do not extend along the entire rift system. Understanding the magmatic-hydrothermal systems is a key priority for future study and hazard assessment.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:683731 |
| Date | January 2015 |
| Creators | Robertson, Elspeth Annabel May |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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