William Hutchison

and 10 more

East Africa hosts significant reserves of untapped geothermal energy. Most exploration has focused on geologically young (<1 Ma) silicic caldera volcanoes, yet there are many sites of geothermal potential where there is no clear link to an active volcano. The origin and architecture of these systems is poorly understood. Here, we combine remote sensing and field observations to investigate a fault-controlled geothermal play located north of lake Abaya in the Main Ethiopian Rift. Soil gas CO2 and temperature surveys were used to examine permeable pathways and showed elevated values along a ~110 m high fault which marks the western edge of the Abaya graben. Ground temperatures are particularly elevated where multiple intersecting faults form a wedged horst structure. This illustrates that both deep penetrating graben bounding faults and near-surface fault intersections control the ascent of hydrothermal fluids and gases. Total CO2 emissions along the graben fault are ~300 t d–1; a value comparable to the total CO2 emission from silicic caldera volcanoes. Fumarole gases show δ13C of –6.4 to –3.8 ‰ and air-corrected 3He/4He values of 3.84–4.11 RA, indicating a magmatic source originating from an admixture of upper mantle and crustal helium. Although our model of the North Abaya geothermal system requires a deep intrusive heat source, we find no ground deformation evidence for volcanic unrest nor recent volcanism. This represents a key advantage over the active silicic calderas that typically host these resources and suggests that fault-controlled geothermal systems offer viable prospects for further exploration and development.

Stanley Tze Hou Yip

and 4 more

Two of the most widely observed co-eruptive volcanic phenomena - ground deformation and volcanic outgassing - are fundamentally linked via the mechanism of magma degassing and the development of compressibility, which controls how the volume of magma changes in response to a change in pressure. Here we use thermodynamic models (constrained by petrological data) to reconstruct volatile exsolution and the consequent changes in magma properties. Co-eruptive SO2 degassing fluxes may be predicted from the mole fraction of exsolved SO2 that develops in magma whilst stored prior to eruption and during decompression. Co-eruptive surface deformation may be predicted given estimates of erupted volume and the ratio between chamber compressibility and magma compressibility. We conduct sensitivity tests to assess how varying magma volatile content, crustal properties, and chamber geometry may affect co-eruptive deformation and degassing. We find that magmatic H2O content has the most impact on both SO2 flux and volume change (normalised for erupted volumes). Our findings have general implications for typical arc and ocean island volcanic systems. The higher magmatic water content of arc basalts leads to a high pre-eruptive exsolved volatile content, making the magma more compressible than ocean island eruptions. Syn-eruptive gas fluxes are overall higher for arc eruptions, although SO2 fluxes are similar for both settings (SO2 flux for ocean island basalt eruptions is dominated by decompressional degassing). Our models are consistent with observation: deformation has been detected at 48% of ocean island eruptions (16/33) during the satellite era (2005-2020), but only 11% of arc basalt eruptions (7/61).

Edna W Dualeh

and 8 more

Satellite radar backscatter has the potential to provide useful information about the progression of volcanic eruptions when optical, ground-based, or radar phase-based measurements are limited. However, backscatter changes are complex and challenging to interpret: explosive deposits produce different signals depending on pre-existing ground cover, radar parameters and eruption characteristics. We use high temporal- and spatial-resolution backscatter imagery to examine the emplacement and alteration of pyroclastic flows, lahars, and ash from the June 2018 eruption of Volcan de Fuego, Guatemala, drawing on observatory reports and rain gauge data to ground truth our observations. We use dense timeseries of backscatter to reduce noise and extract deposit areas. Backscatter decreases where six flows were emplaced on 3 June 2018. In Barranca Las Lajas, we measured a 11.9-km-long flow that altered an area of 6.3 km2; and used radar shadows to estimate a thickness of 10.5 +/- 2 m in the lower sections. The 3 June eruption also changed backscatter over an area of 40 km2, consistent with ashfall. We use transient patterns in backscatter timeseries to identify nine periods of high lahar activity in B. Las Lajas between June and October 2018. We find that the characterisation of subtle backscatter signals associated with explosive eruptions is assisted by (1) radiometric terrain calibration, (2) speckle correction, and (3) consideration of pre-existing scattering properties. Our observations demonstrate that SAR backscatter can capture both the emplacement and subsequent alteration of a range of explosive products, allowing the progression of an explosive eruption to be monitored.