The evolution of hummocky moraine landscapes: a modeling study

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Hummocky moraine topography covers large areas near former ice margins in the once-glaciated continents. A leading hypothesis for the origin of hummocky moraine belts is that they formed from material that accumulated at the surface of a melting, stagnant ice mass. Uneven distribution of englacial and supraglacial sediment and water is expected to cause buried ice to melt at different rates, generating relief on the stagnant, debris-covered surface and promoting lateral and vertical re-sedimentation. While these re-sedimentation processes and the thermal and mechanical factors that control them have been well-described in modern glaciers with relatively thin debris-cover, the way in which they scale spatially and temporally to thicker debris blankets on Pleistocene ice sheets and the landscapes inherited from them is not presently clear. We plan to develop a physical and mathematical framework for modeling long-term ice melt under a thick (0.5m) debris cover and to apply it to testing hypotheses for the origin of hummocky moraine and dominant variables in their formation.This project aims to advance our understanding of and ability to predict melting of ice beneath a thick, insulating layer of rock debris. This problem not only underlies the long-term development of glacier-marginal landscapes (e.g., the hummocky moraine belts of the upper midwestern USA), but is fundamental in the discussion of water resource issues and geological hazards in many parts of the world. Retreating glaciers in places like the Himalayas are increasingly blanketed with rock debris as thinning exposes unstable rock in valley walls. This debris cover modulates glacier melt in a complex way, creating uncertainty among downstream communities in the volume and longevity of a key freshwater resource. Furthermore, debris accumulations atop melting ice have a tendency to be very unstable, creating flooding and debris-flow hazards to nearby people and infrastructure. Our research will combine several modeling tactics and tools, along with geospatial analysis and field observations, to better constrain the key processes and variables controlling melting and debris redistribution in these environments.