Geomorphology, Sediment Budget, and Relief Development in Austdalur, Austfirðir, East Iceland

Abstract

This process-geomorphological study analyzes the present sediment budget in a subarctic oceanic periglacial environment in East Iceland. By a combined investigation of slope denudation and Streamwork in the Austdalur drainage basin (23 km2), located in the mountains of the Icelandic Eastern Fjords (Austfirðir), information on the intensity of the present geomorphological processes, the relative importance of the different processes for slope and valley formation, and recent trends of relief development is presented. In annual mass transfer (t m yr−1), the fluvial sediment transport in the main channels clearly dominates over slope processes. The fluvial transport of solids is more important than the fluvial transport of dissolved salts. The most important slope process with the highest annual mass transfer is aquatic slope denudation (slope and rill wash), followed by geochemical denudation, ground avalanches, rock- and boulder falls, creep, debris slides and flows, and deflation. By the retreat of rock walls and rock ledges and the continued formation of talus cones located below the rock walls and rock ledges, slope processes cause gradual elimination of knickpoints in the slope long profiles and valley widening. The main channels incise into the bedrock of the trough valley floors. There is only a fluvial mass transfer from the slope systems into the main channels in small tributaries. The incision of the tributaries does not keep up with the incision of the main channels. At present the slope systems and the main channel systems are largely decoupled. Postglacial modification of the glacial relief is minor. Because of the short time since the deglaciation (10,000–12,000 yr), the high resistance of the Miocene and Pliocene plateau basalt layers in the area, and the low intensity of the operating periglacial processes, there has been no adjustment of the larger Pleistocene glacial landforms to the geomorphological processes active in the present periglacial morphoclimate.