Integrating remote sensing, field studies and CO2 surveys to unravel structural controls on fluid pathways at a young rift volcano

Abstract:

In volcanically and seismically active rift systems, pre-existing faults can play a significant role in the development of a volcanic complex, ultimately providing high permeability pathways that magma, hydrothermal fluids and gas can ascend to the surface. The Main Ethiopian Rift (MER) provides an ideal natural laboratory to investigate how pre-existing structures influence active volcanic processes because it hosts a number of young volcanic complexes within an active extensional tectonic setting. In this presentation we bring together observations from new high spatial resolution airborne imagery, field campaigns and CO₂ degassing surveys to examine how magma, hydrothermal fluid and gas pathways are coupled to the major structural features on Aluto, a typical young silicic volcanic complex of the MER. Digital mapping of the volcanic complex using new LiDAR DEMs (2-m pixel) reveal that a significant number of lava flow vents and explosion craters on Aluto may be linked to a structural control by either rift-aligned faults that dissect the complex or a volcanic ring fracture. Mapping of surface hydrothermal alteration with aerial photos (<1-m pixel) constrains the location of geothermal fluid upwellings and confirms their links to the main structures. Results of volcanic CO₂ degassing surveys also confirm elevated fluxes (>>100 g m^-2 d^-1) along major faulting and volcanic structures. There are, however, significant variations in CO₂ flux along the fault zones, which can be linked to differences in near surface permeability caused by changes in topography and surface lithology. Overall these different observations of how lava, hydrothermal fluids and gas reach the surface are complementary and provide a strong case for the overarching structural controls on volcanic fluid pathways at present and throughout the evolution of the complex.