Using glaciers to identify, monitor and predict volcanic activity

Martin, Michael Dieter (2023) Using glaciers to identify, monitor and predict volcanic activity. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Globally, ~250 Holocene active volcanoes are either glacier-clad or have glaciers in close proximity. The presence of glaciers on a volcano sometimes masks evidence of volcanic activity and therefore makes direct observations of volcanic activity more challenging if compared to an ‘ice-free’ volcano. However, it is also possible that glaciers can provide indirect information about the activity of the volcanoes on which they sit. With this in mind, the overall aim of this thesis is to assess the degree to which volcanically triggered impacts on glaciers can be observed from optical satellite imagery, and to consider whether these impacts can be used to help identify, monitor and predict volcanic activity. To achieve this, volcanically triggered changes in glacier surface morphology and glacier surface velocity are studied on ice-clad volcanoes using optical satellite images. Approximately 1400 optical satellite images are investigated from key, well-documented eruptions from 1972 to 2015 (i.e., during the satellite remote sensing era) and around the globe. To investigate volcanically triggered changes in surface velocity, glacier velocimetry is performed on Cone Glacier (Mount Veniaminof, Alaska) using 99 Sentinel-2 band 8 images (near-infrared, central wavelength: 842 nm) covering two volcanically active periods, one from September to December 2018 and one in March/April 2021. This approach includes the extraction of velocities along a profile line (following an inferred ice flowline), the generation of time-series velocities, and the calculation of velocity difference maps. The extensive analysis of optical satellite images around the globe shows that the most common observable volcanic impact on glacier morphology (for both thick and thin ice-masses) is ice cauldron and opening formation, often (but not exclusively) associated with concentric crevassing. Other observable volcanic impacts on glacier morphology include ice bulging and fracturing due to subglacial dome growth, localized crevassing due to supraglacial lava flows and widespread glacier crevassing, presumably, due to meltwater-triggered glacier acceleration and advance. Glacier velocimetry results from Cone Glacier show faster glacier surface velocities ~10 months prior to the 2018 volcanically active period and ~2 months prior to the 2021 volcanically active period. Also, an amplified seasonal cycle of faster-than-usual surface velocities in the summer and slower-than-usual surface velocities in the winter is observed during both years with an eruption. Volcanically triggered meltwater is considered as a cause of changing the subglacial drainage at Cone Glacier and is therefore argued as a potential cause of the observed surface velocity changes. The wider applicability of the results to other temperate and polythermal glaciers affected by volcanic activity is discussed. In all, this thesis works towards a deeper understanding of volcanic impacts on glacier morphology and dynamics, elaborates main limitations of using optical satellite images to study ice-clad volcanoes and provides advice for best practice for monitoring glaciers in volcanically active areas.