Dynamics of tidewater surge-type glaciers in northwest Svalbard

The evolution of ice dynamics through surges of four tidewater-terminating glaciers in northwest Svalbard is investigated by remote sensing. A 20 year time series of glacier surface flow speeds and frontal positions is presented covering the recent surges of Monacobreen, Comfortlessbreen, Blomstrandbreen and Fjortende Julibreen. Surface flow speeds were derived using feature tracking between pairs of ERS SAR and ALOS PALSAR images, while frontal positions were taken from the same imagery, as well as more frequent but lower-spatial-resolution Envisat Wide Swath Mode images. During all four surges, increased ice flow caused the tidewater margin to advance while the calving flux was initially reduced to near zero due to compressive stresses limiting crevasse propagation. As ice speed decreased, the terminus continued to advance, until the glacier's speed had returned to its pre-surge flow rate. Only at this time did the terminus start to retreat and peak iceberg calving flux was established. We conclude that terminus advance closely tracks glacier speed-up, that there is little mass loss through calving during the most active phase of the surge, and that seasonal cycles of terminus positions diminish during the active surge phase.