Paraglacial modification of slope form

The morphological consequences of paraglacial modification of valley-side d rift slopes are investigated at six sites in Norway. Here, paraglacial slop e adjustment operates primarily through the development of gully systems, w hereby glacigenic sediment is stripped from the upper drift slope and redep osited in debris cones downslope. This results in an overall lowering of av erage gradient by up to 4.5 degrees along gully axes. In general, slope pro file adjustment appears to be characterized by a convergence of slope profi les towards an 'equilibrium form' with an upper rectilinear slope gradient at 29 degrees +/- 4 degrees 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 degrees, after which parallel retreat appears to predominate. The final form of mature paraglacial gully systems consists of an upper bedrock-floor ed source area, a mid-slope area of broad gullies whose sidewalls rest at s table, moderate gradients, and a lower slope zone where gullies discharge o nto the surfaces of debris cones and fans. Some gullies appear to have atta ined this final form and have stabilized following exhaustion of readily en trainable sediment within decades of gully initiation. At most sites, parag lacial activity has transformed steep drift-mantled valley sides into gulli ed 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 rate s averaging c. 90 mm a(-1) since gully initiation, which highlights the ext reme rapidity of paraglacial erosion of deglaciated drift-mantled slopes. C opyright (C) 1999 John Wiley & Sons, Ltd.