Monitoring glaciers for precursory signs of volcanic activity

Volcanoes can affect overlying glaciers through a variety of processes over a spectrum of spatial and temporal scales. The formation or expansion of melt features (e.g., ice cauldrons) within glaciers have been widely reported as a response to subglacial volcanic unrest and pre-eruptive activity. There are, however, far fewer documented examples of the effects that volcanic unrest may have on individual glacier dynamics. Previous studies have identified higher flow velocities of glaciers near volcanoes, and that some glaciers may speed-up in response to precursory volcanic activity. To investigate the prevalence of such dynamic responses and the potential of using these to inform on volcanic hazards, we carried out a global study of glaciers near volcanoes. We used open-source glacier velocity measurements produced from freely accessible images from the Landsat 4-9, Sentinel-1 and Sentinel-2 satellites. We observed a variety of glacier velocity anomalies, some of which can only be explained as volcanically driven. Of note are velocity anomalies associated with jökulhlaups from subglacial geothermal areas in Iceland, as well as glacier speed-ups concurrent to volcanic unrest at Mount Spurr and precursory to a volcanic eruption of Mount Veniaminof in Alaska. Our results demonstrate the feasibility of using free remote sensing products and open-source code to assist with the monitoring of glacierised volcanoes.