Chapter 17 - Iceland: glacial landforms during deglaciation

Abstract

The spatial and chronological control on the onset of deglaciation of the Iceland ice sheet from the Last Glacial Maximum (LGM) extent is quite loose due to sparse and incoherent data from the shelf and terrestrial areas of Iceland. The deglaciation may have initiated through ice sheet thinning as early as 26calka BP but the onset of significant retreat from the LGM peak extent likely occurred around 22calka BP. Conspicuous moraines on the mid to inner Iceland shelf probably represent stillstands during the overall retreat from the LGM position but remain to be dated directly. Major troughs on the western and northern shelf remained glaciated until 15.3calka BP. At that time, the marine-based parts of the IIS collapsed, and the ice sheet margin was inside the present coast at 14.6calka BP when marine limit shorelines were formed. This yields a time frame of 600–700 years for the collapse with an average retreat rate of 0.2km/year and ice loss mainly through intensive calving that was driven by rising sea level. Cosmogenic exposure dates from coastal mountains in the West Fjords and central north Iceland indicate that the collapse was preceded by ice sheet thinning and retreat. At present, there is ample room for improving the deglaciation chronology of the IIS through more basal dates from the Iceland shelf, not least the eastern and southern sectors, as well as exposure dates from coastal areas.