Magmatic degassing at the East African Rift volcanoes

: evaluating rifting processes and geothermal resources

Abstract

There is a growing recognition that the EARS volcanoes are important emitters of magmatic volatiles, particularly CO₂. The Ethiopian Rift, which forms the northern section of the EARS, particularly hosts many volcanoes and offers an ideal setting to interrogate magmatic gas emissions in an active rift setting. Yet, both the magnitude of these emissions and the processes that control them remain poorly constrained. This thesis explores the magnitude and structural controls of gas emissions at two big and most active calderas; Bora-Baricha-Tulu Moye (BBTM) and Corbetti. I use new soil CO₂ flux measurements and fumarole gas geochemistry to identify zones of high permeability and to understand the magmatic sources contributing to gas release at these volcanoes.

BBTM was found to be the highest volcanic CO₂ emitter in the region, with fluxes of 276–329 kt yr⁻¹. It also shows the highest mantle plume-like like ³He/⁴He values (up to 17 Ra), yet observed in the rift, indicating strong deep mantle volatile sources. Corbetti, in contrast, exhibited lower emissions (79 ± 22 t d⁻¹) and its magmatic gases more affected by atmospheric contaminations. In both calderas, tectonic faults dissecting them provide key pathways for volatile release. I revise the total CO₂ emissions from the Ethiopian rift to 2.5–9.2 Mt yr⁻¹. To gain the rift scale perspective on the relationship between mantle sources, magmatism and degassing, I compile Helium isotopes in rocks and gases from across Ethiopia and compare this to geophysical images of mantle melting. The findings reveal a spatial correlation between gas emissions and regions of elevated mantle melt production and magmatism along the rift.

Finally, I applied thermal remote sensing using Landsat 8 data to detect geothermal anomalies at Aluto. Nighttime images successfully identified 60% of known fumaroles, demonstrating the effectiveness of satellite-based monitoring in geothermal exploration.

Date of Award	3 Jul 2026
Original language	English
Awarding Institution	University of St Andrews
Supervisor	William Hutchison (Supervisor), C. Richard Bates (Supervisor) & Eva Stueeken (Supervisor)