Modelling Periglacial Processes on Low-Relief High-Elevation Surfaces

Abstract:

Are low-relief high-elevation surfaces generally a result of uplift of flat surfaces formed close to sea-level or can they be formed "in situ" by climate dependent surface processes such as those associated with glaciation? This question is important to resolve in order to understand the geological history in many regions of the world.

The glacial buzzsaw concept suggests that intense glacial erosion focused at the equilibrium-line altitude (ELA) leads to a concentration in surface area close to the ELA. However, even in predominantly glacial landscapes, such as the Scandinavian Mountains, the high surfaces often have nonglacial characteristics and show pre-glacial inheritance of cosmogenic nuclide concentrations. This suggests that subglacial erosion is not the dominant erosion mechanism.

Anderson (2002) showed that periglacial frost-driven processes working over timescales of millions of years form low-curvature parabolic surfaces at accordant elevation across intervening valleys. The rate of these erosion processes is limited by the slow diffusive transport of regolith in the periglacial domain.

We elaborate on this idea by quantifying frost cracking and frost creep in a numerical model as a function of mean annual air temperature and sediment thickness. This allows us to incorporate periglacial processes into a long-term landscape evolution model where surface elevation, sediment thickness, and climate evolve over time. With this model we are able to explore the slow feedbacks between periglacial erosion, sediment transport, and the evolving topography. We show that smooth peaks, convex hillslopes, and a few meters thick regolith cover at high elevation are emergent properties of the landscape evolution model. By varying climate and other model parameters, we discuss how the landscape evolution model can be used for obtaining more insight into the conditions needed for formation of low-relief surfaces at high elevation.

Anderson, R. S. Modeling the tor-dotted crests, bedrock edges, and parabolic profiles of high alpine surfaces of the Wind River Range, Wyoming. Geomorphology, 46, 35-58 (2002).