Localized uplift of Vatnajokull, Iceland: subglacial water accumulation deduced from InSAR and GPS observations

摘要

We report on satellite and ground-based observations that link glacier motion withsubglacial hydrology beneath Skeioararjokull, an outlet glacier of Vatnajokull, Iceland. We havedeveloped a technique that uses interferometric synthetic aperture radar (InSAR) data, from theEuropean Remote-sensing Satellite (ERS-1/-2) tandem mission (1995-2000), to detect localizedanomalies in vertical ice motion. Applying this technique we identify an area of the glacier wherethese anomalies are frequent: above the subglacial course of the river Skeioara, where we observeduplift of 0.15-0.20 md~(-1)during a rainstorm and jokulhlaup, subsidence at a slower ratesubsequent to rainstorms. A similar pattern of motion is apparent from continuous GPS measurementsobtained at this location in 2006/07. We argue that transient uplift of the ice surface is caused by wateraccumulating at the glacier base upstream of an adverse bed slope where the overburden pressuredecreases significantly over a short distance. Most of the frictional energy of the flowing water istherefore needed to maintain water temperature at the pressure-melting point. Hence, little energyis available to enlarge water channels sufficiently by melting to accommodate sudden influxes of waterto the base. This causes water pressure to exceed the overburden pressure, enabling uplift to occur.