| Abstract: | The morphological consequences of paraglacial modification of valley-side drift slopes are investigated at six sites in Norway. Here, paraglacial slope adjustment operates primarily through the development of gully systems, whereby glacigenic sediment is stripped from the upper drift slope and redeposited in debris cones downslope. This results in an overall lowering of average gradient by up to 4·5° along gully axes. In general, slope profile adjustment appears to be characterized by a convergence of slope profiles towards an ‘equilibrium form’ with an upper rectilinear slope gradient at 29°± 4° and a range of concavities of approximately 0·0 to 0·4. After initial rapid incision, further gully deepening is limited, but gullies become progressively wider as sidewall gradients decline to c. 25°, after which parallel retreat appears to predominate. The final form of mature paraglacial gully systems consists of an upper bedrock-floored source area, a mid-slope area of broad gullies whose sidewalls rest at stable, moderate gradients, and a lower slope zone where gullies discharge onto the surfaces of debris cones and fans. Some gullies appear to have attained this final form and have stabilized following exhaustion of readily entrainable sediment within decades of gully initiation. At most sites, paraglacial activity has transformed steep drift-mantled valley sides into gullied slopes where an average of c. 2–3 m of surface lowering has taken place. At the most active sites, these average amounts imply minimum erosion rates averaging c. 90 mm a−1 since gully initiation, which highlights the extreme rapidity of paraglacial erosion of deglaciated drift-mantled slopes. Copyright © 1999 John Wiley & Sons, Ltd. |
