An exploration of volcanic controls on glacier velocity

Approximately 17% of the Earth’s 1,413 Holocene volcanoes are glacier covered or possess at least one glacier within a radius of 5 km. Glacier-volcano interactions are therefore relatively common, yet our understanding of these interactions is hindered by a sparsity of observations and a lack of quantitative data. Furthermore, glaciovolcanicanism has been implicated in a number of particularly deadly and costly volcanic eruptions in recent decades. Documenting and quantifying the impacts of glacier-volcano interactions is therefore increasingly needed to both accurately forecast the future dynamics of volcanic glaciers and mitigate associated glaciovolcanic hazards.

Encouragingly, recent research has shown that optical satellite imagery can be used to detect volcanic impacts on glacier surface morphology, such as the development of ice cauldrons and widespread crevassing. However, to date the capacity of volcanic activity to influence glacier velocities and wider glacier geometry remains relatively unexplored. Here, we present a comparative study of volcanic and non-volcanic glacier velocities and geometries. We apply descriptive and multivariate statistical analyses to a broad range of glacial, volcanic and climate records in order to: i) compare volcanic and non-volcanic glacier parameters globally for the year 2017/18, and ii) investigate relationships between volcano properties and volcanic glacier characteristics.

Our final dataset comprises ~2,700 volcanic glaciers and ~210,000 non-volcanic glaciers. We reveal that volcanic glaciers typically exhibit greater and more variable velocities than their non-volcanic counterparts, with an average median velocity of 18.09 ma^‑1 versus 7.94 ma^-1 for non-volcanic glaciers. We also find that volcanic glaciers are typically larger, longer and thicker than non-volcanic glaciers, and are more likely to be situated at lower elevations, on more gentle slopes in warmer, wetter climates than their non-volcanic counterparts. However, when controlling for these differences in glacier geometry, situation and climate, we find that the greater velocities observed for volcanic glaciers remain statistically significant. Relationships between volcano properties and volcanic glacier characteristics tentatively indicate that volcano type and tectonic setting may also act as controls on volcanic glacier velocities, and that the greatest volcanic glacier velocities are typically found in glaciers situated closest to volcanoes.

The enhanced velocities documented here, particularly for glaciers most proximal to volcanoes, are hypothesised to be a consequence of locally increased geothermal heat inputs. Consequently, we contend that the velocities of volcanic glaciers may be a valuable proxy for volcanic activity and, with further investigation, may provide considerable potential for monitoring and forecasting volcanic activity, and for improving the mitigation of glaciovolcanic hazards.