Volume changes of Vatnajökull ice cap, Iceland, due to surface mass balance, ice flow, and subglacial melting at geothermal areas

We present observed changes in the geometry of western Vatnajökull over a period of about ten years which are caused by the surface mass balance, ice flow (both during surges and quiescent periods), and basal melting due to geothermal and volcanic activity. Comparison of two digital elevation models shows that from 1985 to 1998 the outlet glaciers have lost 14 ± 5 km3, on the average 1 m yr−1 evenly distributed over the area of 1360 km2. However, the marginal areas of four outlets have gained up to 80 m in elevation and the uppermost parts have subsided similarly during surges. Altogether 26 ± 3 km3 were transported from the accumulation areas to the ablation areas of which 19 ± 3 km3 are attributed to surges. Comparison of DEM's from August 1997 and August 1998 revealed 10 ice cauldrons produced by subglacial geothermal activity, of which some were previously unknown.