Characterising the explosive history of Kenyas geothermal powerhouse in the East African Rift: The Greater Olkaria Volcanic Complex

Improved forecasting and management of volcanic hazards demands a better understanding of the eruptive processes that regulate them. Over the last two decades, a plethora of observational, analytical and experimental datasets have greatly improved our knowledge of volcanic processes. However, such data has primarily been derived from well monitored subduction-related volcanoes where magma is chemically distinct (calc-alkaline vs. alkaline) and eruption repose times are significantly shorter (monthsyears vs. centuries) compared to relatively poorly monitored and studied continental rift settings. The East African Rift (EAR) represents a classic example of continental rifting, hosting ~100 active (Holocene) volcanoes in densely populated areas, bringing significant risk together with socio-economic advantages to those living in close proximity. This is particularly the case in the southern Kenya Rift, a magma-assisted segment in the intermediate-advanced stage of rifting, where volcanoes are experiencing active deformation and CO2-degassing indicative of the presence of shallow magmatic reservoirs. In this study we focus on the Greater Olkaria Volcanic Complex (GOVC), a model example of a young (<20 ka), multicentred (ca. 80 in a ~240km2 area) and frequently erupting peralkaline rhyolitic caldera, displaying evidence for a range of activity from benign lava effusion to catastrophic explosive tephra dispersal. Olkaria has been exploited as a geothermal field since 1981 and currently stands as Kenyas single most important geothermal energy resource. Effusive activity has been well documented and geochemically assessed, yet constraints on the explosive activity (frequency-magnitude relationships, pre-eruptive magmatic conditions/processes) remain relatively unexplored and form an integral part of GOVCs history. Here we present preliminary results from two field campaigns (carried out in Nov 2020 and JulAug 2021) to characterise the explosive history of the system through a combination of tephrostratigraphic field observations, along with petrological and geochemical analyses of tephra deposits that erupted throughout the evolution of GOVC.