Factors that contribute to the elongation of drumlins beneath the Green Bay Lobe, Laurentide Ice Sheet,Earth Surface Processes and Landforms

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Factors that contribute to the elongation of drumlins beneath the Green Bay Lobe, Laurentide Ice Sheet
Earth Surface Processes and Landforms ( IF 2.8 ) Pub Date : 2021-07-06 , DOI: 10.1002/esp.5192
L. K. Zoet ₁ , J. E. Rawling ₂ , J. Woodard ₁ , N. Barrette _{1,

3} , D. M. Mickelson ₁

Affiliation

Drumlin shape has been hypothesized to correlate with ice-flow duration and slip speed, but modern-day analogues and the Coulomb nature of till render the basis of these correlations in question. The evolution of flow-parallel subglacial landforms is of importance for ice flow because the form drag they provide may be a dominant factor in regulating glacier slip speeds. Here we examine the relationship between drumlin shape and cumulative slip displacement (i.e. time-integrated slip speed) as a dominant glaciological control on drumlin shape. First, a new method is developed that allows slip speed to be estimated for deformable bedded glaciers along a flow line from an ice surface profile. Then, reconstructed surface profiles for ice margin chronologies of the Green Bay Lobe (GBL) are used to construct and estimate the spatially varying cumulative slip displacement for use in comparison with drumlin elongation ratios. We focus on a sector of the GBL near the central flow line where the geology is simple and glaciological controls are likely to dominate bedform development. Using Bayesian statistical analysis, a positive and statistically robust relationship between cumulative slip displacement and drumlin elongation ratio is found. Our analysis indicates that drumlin shape could be used to infer palaeo glacier slip speeds if time under the ice can be well constrained and geologic influences are minimal. These findings also suggest that drumlin-supplied drag could decrease with increased cumulative slip displacement in the absence of rigid geologic features that fix drumlin positions.

中文翻译：

导致劳伦泰德冰盖绿湾叶下鼓音伸长的因素

鼓林形状已被假设与冰流持续时间和滑动速度相关，但现代类似物和直到的库仑性质使这些相关性的基础成为问题。平行流动的冰下地貌的演变对冰流很重要，因为它们提供的形式阻力可能是调节冰川滑动速度的主要因素。在这里，我们研究了鼓形形状和累积滑动位移（即时间积分滑动速度）之间的关系，作为对鼓形形状的主要冰川控制。首先，开发了一种新方法，可以根据冰面剖面沿流线估计可变形层状冰川的滑动速度。然后，绿湾叶 (GBL) 冰缘年代学的重建表面轮廓用于构建和估计空间变化的累积滑动位移，以与鼓膜伸长率进行比较。我们关注中央流线附近的 GBL 部分，该部分地质简单，冰川控制可能主导床型发育。使用贝叶斯统计分析，发现累积滑动位移和鼓膜伸长率之间存在正和统计上稳健的关系。我们的分析表明，如果可以很好地限制冰下时间并且地质影响最小，则鼓槌形状可用于推断古冰川滑动速度。

更新日期：2021-07-06

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