Geomorphological observations on Sermersôq. A contribution to the geomorphology of S. Greenland

Abstract

On the island of Sermersôq four erosion surfaces have been recognized, which are of regional importance in S Greenland. Their development is related to three cycles of erosion, interrupted by two glacial stages. The high-level erosion surface at altitudes above 1000 m is the remnant of an old peneplane, which was formed during the oldest erosion cycle and uplifted in late Cretaceous or early Tertiary times. This uplift initiated a second erosion cycle in the course of which a main glacial stage intervened. In this glacial stage the icelevel in the main valleys (the present fjords) acted as the effective base level of erosion and this resulted in the formation of stretches of an intermediate-level erosion surface, which now occur along the main fjords at altitudes between 400 m and 650 m. An important lowering of effective base level of erosion occurred when in the subsequent interglacial stage the sea-level resumed its role as the effective base level of erosion. This event initiated a third erosion cycle in the course of which the low-level erosion surface, between 100 m and 250 m altitude, and the strandflat, a coastal platform below 50 m, were formed. The third erosion cycle was interrupted by a second glacial stage, which on Sermersôq has the localized character of a mountain glaciation; it is during this second glacial stage that the present day fretted upland morphology of central Sermersôq originated. Post-glacial vertical movements causing the emergence of the strandflat induced a rejuvenation of erosion and consequently the incision of this coastal platform and valley floors by recent rivers.