Abstract
In volcanically and seismically active rift systems, preexisting faults may control the rise and eruption of magma, and direct the flow of hydrothermal fluids and gas in the subsurface. Using high-resolution airborne imagery, field observations, and CO 2 degassing data on Aluto, a typical young silicic volcano in the Main Ethiopian Rift, we explore how preexisting tectonic and volcanic structures control fluid pathways and spatial patterns of volcanism, hydrothermal alteration and degassing. A new light detection and ranging (lidar) digital elevation model and evidence from deep geothermal wells show that the Aluto volcanic complex is dissected by rift-related extensional faults with throws of 50–100 m. Mapping of volcanic vent distributions reveals a structural control by either rift-aligned faults or an elliptical caldera ring fracture. Soil-gas CO 2 degassing surveys show elevated fluxes (>>100 g m –2 d –1 ) along major faults and volcanic structures, but significant variations in CO 2 flux along the fault zones reflect differences in near-surface permeability caused by changes in topography and surface lithology. The CO 2 emission from an active geothermal area adjacent to the major fault scarp of Aluto amounted to ∼60 t d –1 ; we estimate the total CO 2 emission from Aluto to be 250–500 t d –1 . Preexisting volcanic and tectonic structures have played a key role in the development of the Aluto volcanic complex and continue to facilitate the expulsion of gases and geothermal fluids. This case study emphasizes the importance of structural mapping on active rift volcanoes to understand the geothermal field as well as potential volcanic hazards.
Highlights
Existing fault structures can play a significant role in the development of a volcanic complex, providing high permeability pathways for magma, hydrothermal fluids, and gas to ascend to the surface (e.g., Arnórsson, 1995; Rowland and Sibson, 2004; Caliro et al, 2005; Fridriksson et al, 2006)
These local influences may include (1) lithological variations, where fluids will preferentially migrate along high permeability layers and (2) topographic controls, where the stress field induced by gravitational loading causes fracturing parallel to topography, and focuses pathways for steam and other gases toward topographic highs (Schöpa et al, 2011)
From these data we develop a conceptual model that captures both the volcanic evolution and the role these major structures play in controlling fluid pathways
Summary
Existing fault structures can play a significant role in the development of a volcanic complex, providing high permeability pathways for magma, hydrothermal fluids, and gas to ascend to the surface (e.g., Arnórsson, 1995; Rowland and Sibson, 2004; Caliro et al, 2005; Fridriksson et al, 2006). To understand how large-scale structures influence active volcanic processes it is useful to look at the surface expression of different volcanic fluids (i.e., magma, hydrothermal fluids, and gas) across a variety of scales to disentangle largescale structural controls from these localized near-surface permeability variations Both direct and remote measurements can be used to assess the spatial distribution of fluids and fluid pathways. Volcanic gases (e.g., CO2) that may be difficult to detect remotely, can be readily measured in the field using modern surveying techniques (Chiodini et al, 1998) and gridded to produce detailed maps of gas flux across a volcanic edifice (Cardellini et al, 2003; Parks et al, 2013) These techniques allow us to build detailed pictures of how different fluids are released from active volcanoes; the challenge for volcanologists is integrating these observations to unravel the subsurface structure and the processes controlling fluid pathways
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
