Title:
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Magma storage and transport at Kenyan Rift volcanoes : a remote sensing perspective
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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.
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