The Role of Paraglacial and Periglacial Processes in Shaping Glacial Valleys: Example from NW Iceland

Are U-shaped valleys, long regarded as the exclusive result of glacial erosion, significantly shaped by processes occurring during interglacial periods? This study challenges conventional glacial geomorphology by quantifying the sedimentary contributions of interglacial sequences.

Focusing on the Nesdalur valley in Iceland's Westfjords—a U-shaped valley sculpted by repeated glaciation-deglaciation cycles and marked by its Tertiary basalt structure—we investigate the role of slope dynamics. The valley’s geomorphological evolution is analyzed through a volumetric approach using high-resolution (2m x 2m) Digital Elevation Models (DEM) to estimate sediment production from paraglacial rock-slope failures (RSFs) and periglacial scree over the current interglacial period.

Our results show that interglacial processes, including slope retreat driven by 11 identified RSFs, have contributed between 1% and 4% of the valley's present volume: mainly paraglacial RSF (68%) and periglacial scree (32%). By extrapolating these data, we estimate that approximately 22 interglacial periods could account for up to 48% of the valley’s denudation. While glacial activity remains essential for sediment evacuation, this study highlights the substantial sedimentary impact of interglacial sequences in valley widening.

These findings advocate for a more integrative understanding of U-shaped valleys, positioning interglacial sedimentary dynamics as key drivers of valley morphology. By quantifying the sedimentary contributions of interglacial sequences, this research highlights the complementary roles of glacial and interglacial processes in shaping valleys.