The evolution of hummocky moraine landscapes: a modeling study

在曾经被冰川覆盖的大陆上，丘状冰碛地形覆盖了以前冰缘附近的大片地区。关于丘状冰碛带起源的一个主要假设是，它们是由融化的、停滞的冰块表面积累的物质形成的。冰川和冰上沉积物和水的不均匀分布预计会导致埋藏冰以不同的速度融化，在停滞的、被碎屑覆盖的表面产生起伏，并促进横向和垂直再沉积。虽然这些再沉积过程以及控制它们的热和机械因素已经在具有相对较薄的碎屑覆盖的现代冰川中得到了很好的描述，但它们在空间和时间上扩展到更新世冰盖上较厚的碎屑覆盖层的方式以及从中继承的景观目前尚不清楚。我们计划开发一个物理和数学框架，用于模拟厚（0.5米）碎屑覆盖下的长期冰融化，并将其应用于测试丘状冰碛起源的假设及其形成中的主要变量。这个项目旨在提高我们对厚而绝缘的岩屑层下冰融化的理解和预测能力。这个问题不仅是冰川边缘景观（如美国中西部上部的丘状冰碛带）长期发展的基础，也是世界许多地区水资源问题和地质灾害讨论的基础。在喜马拉雅山等地，由于冰川变薄，山谷壁上不稳定的岩石暴露出来，退缩的冰川越来越多地被岩石碎片覆盖。这种碎片覆盖以一种复杂的方式调节冰川融化，给下游社区造成了一种关键淡水资源的数量和寿命的不确定性。此外，融化的冰上堆积的碎片往往非常不稳定，给附近的居民和基础设施造成洪水和泥石流的危险。我们的研究将结合几种建模策略和工具，以及地理空间分析和实地观测，以更好地约束这些环境中控制融化和碎片再分布的关键过程和变量。

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.