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Absent drumlins beneath southern lobes of the Laurentide Ice Sheet: A new hypothesis based on Des Moines Lobe dynamics inferred from landforms
Earth Surface Processes and Landforms ( IF 2.8 ) Pub Date : 2023-08-30 , DOI: 10.1002/esp.5690 Neal R. Iverson 1 , Sarah E. Krueger 1 , Chris Harding 1
Earth Surface Processes and Landforms ( IF 2.8 ) Pub Date : 2023-08-30 , DOI: 10.1002/esp.5690 Neal R. Iverson 1 , Sarah E. Krueger 1 , Chris Harding 1
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Spatial distributions of drumlin fields encode information about ice sheet dynamics. No drumlins formed beneath the most lobate parts of the Laurentide Ice Sheet's southern margin, in South Dakota, Iowa and Illinois, whereas ice lobes to the northeast generally produced drumlins. This pattern may have resulted from northerly ice overriding permafrost. Here we propose a new hypothesis for this pattern by constructing a LiDAR-based landform map and applying a model of drumlin formation to account for the absence of drumlins beneath the largest of the ice sheet's southern lobes, the Des Moines Lobe. Broad belts of hummocky topography, ice-walled lake plains, doughnuts and minor moraines, which together cover 90% of the lobe's upland area in Iowa, attest to widespread ice stagnation, as does the lobe's scarcity of eskers. Most stagnation topography is subtle, with insufficient relief to have obscured drumlins that might have formed before stagnation. Minor moraines are crevasse-squeeze ridges diagnostic of surging, and their ubiquity indicates that during surging, the lobe's soft bed was weak nearly everywhere. End moraines are generally parallel to a minor moraine setup-glacier, implying that surge-driven advances were more numerous than indicated by the three major end moraines of the lobe. In the only physically based model of drumlin formation that includes surging, till deposition occurs during surges when effective pressure is uniformly low, whereas drumlins develop during quiescent flow between surges, when basal slip and low-pressure R-channels create the spatial gradients in effective pressure necessary to sculpt drumlins by differential erosion. Landforms of the lobe, however, indicate stagnation and down-wasting during quiescence, without significant basal slip or hydraulic potential gradients necessary for R-channels. We hypothesize that for the three southernmost lobes of the Laurentide Ice Sheet, surging followed by widespread down-wasting of stagnant ice prevented drumlin formation, whereas beneath northern lobes it was permitted by climatically-forced ice advance.
中文翻译：
劳伦泰冰盖南叶下方不存在鼓丘：基于从地貌推断的得梅因南叶动力学的新假设
鼓林场的空间分布编码有关冰盖动力学的信息。在南达科他州、爱荷华州和伊利诺伊州，劳伦泰德冰原南缘最有裂片的部分下方没有形成鼓丘，而东北部的冰裂通常会产生鼓丘。这种模式可能是由于北冰覆盖永久冻土层造成的。在这里，我们通过构建基于激光雷达的地形图并应用鼓林形成模型来解释这种模式的新假设，以解释冰盖最大的南叶（得梅因洛贝）下方不存在鼓林的情况。宽阔的丘陵地貌带、冰墙湖平原、甜甜圈和小冰碛，它们共同覆盖了爱荷华州 90% 的冰叶高地区域，证明了广泛的冰停滞，以及冰叶缺乏埃斯克。大多数停滞地貌都很微妙，没有足够的地形来掩盖停滞前可能形成的鼓点。小冰碛是诊断涌动的裂缝挤压山脊，它们的普遍存在表明在涌动期间，波瓣的软床几乎到处都很脆弱。末端冰碛一般与小冰碛装置-冰川平行，这意味着涌动驱动的前进数量比波瓣的三个主要末端冰碛所显示的数量更多。在唯一基于物理的鼓膜形成模型中，包括涌动，直到在有效压力一致较低的浪涌期间发生沉积，而鼓膜在涌动之间的静态流动期间形成，此时基底滑移和低压 R 通道在有效压力中产生空间梯度。通过差异侵蚀雕刻鼓皮所需的压力。然而，叶的地形表明静止期间的停滞和向下消耗，没有明显的基底滑移或 R 通道所需的水力梯度。我们假设，对于劳伦太德冰盖最南端的三个冰片，汹涌的冰块随后大范围地向下消耗，阻止了鼓鼓的形成，而在北冰片下方，气候迫使冰的前进允许了鼓鼓的形成。
更新日期：2023-08-30
中文翻译：
劳伦泰冰盖南叶下方不存在鼓丘：基于从地貌推断的得梅因南叶动力学的新假设
鼓林场的空间分布编码有关冰盖动力学的信息。在南达科他州、爱荷华州和伊利诺伊州，劳伦泰德冰原南缘最有裂片的部分下方没有形成鼓丘，而东北部的冰裂通常会产生鼓丘。这种模式可能是由于北冰覆盖永久冻土层造成的。在这里，我们通过构建基于激光雷达的地形图并应用鼓林形成模型来解释这种模式的新假设，以解释冰盖最大的南叶（得梅因洛贝）下方不存在鼓林的情况。宽阔的丘陵地貌带、冰墙湖平原、甜甜圈和小冰碛，它们共同覆盖了爱荷华州 90% 的冰叶高地区域，证明了广泛的冰停滞，以及冰叶缺乏埃斯克。大多数停滞地貌都很微妙，没有足够的地形来掩盖停滞前可能形成的鼓点。小冰碛是诊断涌动的裂缝挤压山脊，它们的普遍存在表明在涌动期间，波瓣的软床几乎到处都很脆弱。末端冰碛一般与小冰碛装置-冰川平行，这意味着涌动驱动的前进数量比波瓣的三个主要末端冰碛所显示的数量更多。在唯一基于物理的鼓膜形成模型中，包括涌动，直到在有效压力一致较低的浪涌期间发生沉积，而鼓膜在涌动之间的静态流动期间形成，此时基底滑移和低压 R 通道在有效压力中产生空间梯度。通过差异侵蚀雕刻鼓皮所需的压力。然而，叶的地形表明静止期间的停滞和向下消耗，没有明显的基底滑移或 R 通道所需的水力梯度。我们假设，对于劳伦太德冰盖最南端的三个冰片，汹涌的冰块随后大范围地向下消耗，阻止了鼓鼓的形成，而在北冰片下方，气候迫使冰的前进允许了鼓鼓的形成。
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