Borehole-Based Characterization of Deep Mixed-Mode Crevasses at a Greenlandic Outlet Glacier
Borehole-Based Characterization of Deep Mixed-Mode Crevasses at a Greenlandic Outlet Glacier
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DOI：
10.1029/2020av000291
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发表时间：
2021-06-01
期刊：
影响因子：
8.4
通讯作者：
Bougamont, Marion
中科院分区：
文献类型：
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作者：
Hubbard, Bryn;Christoffersen, Poul;Bougamont, Marion
在格陵兰岛快速移动的Store冰川的一个裂缝区域进行光学电视钻孔测井，揭示了35个高角度平面的存在，这些平面穿过背景初级分层。这些平面是由无气泡的再冻结冰层组成的，其中大部分是富含气泡的“最后冻结”冰的薄层，这与平面是以前开放裂缝的痕迹相一致。在四个痕迹中观察到几个这样的最后冻结层，表明裂缝重新激活的多次发作。裂缝痕迹的出现频率一般随深度的增加而减少，最深的可探测痕迹在地表以下265 m处。这与该地区比模拟温度更高的冰川的范围相一致，从表面延伸到大约400米的深度。裂缝迹向强烈聚集在倾角63°和走向与主扩展应变局部方向正交偏移71°附近。因此，这些痕迹的先前裂缝被解释为起源于冰川上，可能类似于8公里远的混合模式（I和III）形成。我们得出结论，深裂缝在Store冰川中普遍存在，因此在所有动态相似的出口冰川中也是如此。一旦愈合，它们的痕迹就代表了脆弱的平面，在随后的冰川平流中会重新激活。考虑到它们的深度，这些痕迹——尤其是那些在冰川下形成的痕迹——很有可能在表面消融后幸存下来，到达冰川终点，在那里它们可能成为断裂和冰山崩解的焦点。
Optical televiewer borehole logging within a crevassed region of fast-moving Store Glacier, Greenland, revealed the presence of 35 high-angle planes that cut across the background primary stratification. These planes were composed of a bubble-free layer of refrozen ice, most of which hosted thin laminae of bubble-rich "last frozen" ice, consistent with the planes being the traces of former open crevasses. Several such last-frozen laminae were observed in four traces, suggesting multiple episodes of crevasse reactivation. The frequency of crevasse traces generally decreased with depth, with the deepest detectable trace being 265 m below the surface. This is consistent with the extent of the warmer-than-modeled englacial ice layer in the area, which extends from the surface to a depth of similar to 400 m. Crevasse trace orientation was strongly clustered around a dip of 63 degrees and a strike that was offset by 71 degrees from orthogonal to the local direction of principal extending strain. The traces' antecedent crevasses were therefore interpreted to have originated upglacier, probably similar to 8 km distant involving mixed-mode (I and III) formation. We conclude that deep crevassing is pervasive across Store Glacier, and therefore also at all dynamically similar outlet glaciers. Once healed, their traces represent planes of weakness subject to reactivation during subsequent advection through the glacier. Given their depth, it is highly likely that such traces-particularly those formed downglacier-survive surface ablation to reach the glacier terminus, where they may represent foci for fracture and iceberg calving.