Reduced glacier sliding caused by persistent drainage from a subglacial lake

摘要

We present velocity observations of a glacier outlet in Vatnaj?kull,Iceland, deduced from interferometric SAR (InSAR) data obtained during theERS1/2 tandem mission in 1995–2000. More than a 50% decrease in glaciervelocity was observed subsequent to a large j?kulhlaup from thesubglacial lake Grímsv?tn in 1996. The glacier had not reached itsformer flow rate in 2000. The j?kulhlaup damaged the lake's ice-damcausing persistent drainage from the lake. InSAR based studies of wateraccumulation within Grímsv?tn suggest that a leakage of >3 m3 s−1prevailed throughout our study period. We suggest that thelake leakage kept open a tunnel at low water pressure underneath the wholelength of the glacier. The tunnel flow drained water from its surroundings,hence lowering the water pressure of a distributed drainage system,underneath the upper and centre parts of the glacier, which prior to thej?kulhlaup sustained significant basal sliding. This is in accordancewith theoretical prediction that tunnel flow in a steady state may causeslow-down in glacier velocity by reducing the subglacial water pressure. Thewidth of the affected areas was ~5 km on the upper part of the glacierand ~8 km on the centre part of the glacier. This indicates that thewater pressure reduction propagates laterally from the tunnel over adistance of a few km.