An investigation of active subglacial thrust glaciotectonics and its role in stick-slip motion from Skalafellsjokull, Iceland

Glacier basal movement is by sliding, sediment shearing, or sediment shearing at depth. This movement can either be constant, or discontinuous via stick-slip motion. This is controlled by the interrelationship between pore water pressure and till rheology. There have been very few modern observations of subglacial shearing at depth, although glaciotectonic thrust sheets have been commonly reported from Quaternary and modern glacier forelands. Skalafellsjökull, Iceland represents a rare opportunity to study this style of basal movement. Ground penetrating radar (GPR) studies made in 2008 and 2011 showed that thrust slices of till were present beneath the glacier, and the amount of movement of these slices could be measured. Sediments exposed in the foreland also demonstrated that thin slices of till had been glaciotectonically deformed. We use this data combined with a 2 year record from the Glacsweb subglacial wireless probe, and passive seismics to investigate the relationship between subglacial shearing at depth and stick-slip motion.