Structural evolution of a surge-type polythermal glacier: Hessbreen, Svalbard
Structural evolution of a surge-type polythermal glacier: Hessbreen, Svalbard
复制标题
涌动型多温冰川的结构演化：斯瓦尔巴特群岛赫斯布林
作者：
M. Hambrey;J. Dowdeswell
赫斯布林是一个小山谷冰川，最后一次激增是在1974年，是斯瓦尔巴特群岛许多多温冰川的典型代表。目前的冰面显示出广泛的结构，可以归因于静止相或浪涌相变形。在静止相流，初级分层成为轻微变形成低振幅开放褶皱，而一个全新的结构，纵向叶理，发展在轴向平面关系，这些褶皱。涌浪前缘的传播与冲断层的形成有关;然而，并不是所有冲断层都能突破地表。随着涌浪的发展，涌浪前缘后面的冰变得伸展，冰川表面破裂成许多裂缝，其中几百米长的横向裂缝，凸上冰川，是主要的。经过一段时间的平静，这些成为退化的裂缝痕迹，平面结构是陡峭的倾斜，并有许多不同的方向。总的来说，大部分到达吻部的冰并没有经历显著的累积应变，正如主要结构和后来的裂缝痕迹都没有变形所表明的那样。Hessbreen的碎片分布在很大程度上受到其中一些结构的发展的控制。有角度的冰上碎屑与分层密切相关，而基底碎屑被提升到冰上和冰上位置与逆冲作用有关。
Hessbreen is a small valley glacier which last surged in 1974, and is typical of many polythermal glaciers in Svalbard. The present ice surface displays a wide range of structures that can be attributed to either quiescent-phase or surge-phase deformation. During quiescent-phase flow, primary stratification becomes slightly deformed into low-amplitude open folds, while a completely new structure, longitudinal foliation, develops in axial-planar relationship to these folds. The propagation of a surge front is associated with the formation of thrusts; however, not all of these break through to the surface. As the surge progresses, and the ice behind the surge front becomes extensional, the surface of the glacier breaks up into numerous crevasses, of which several hundred metre long transverse crevasses, convex up-glacier, are dominant. After a period of quiescence, these become degraded into crevasse traces, planar structures which are steeply dipping and have many different orientations. Overall, most ice which reaches the snout has not undergone significant cumulative strain, as indicated by the lack of deformation of both the primary structures and the later crevasse traces. The distribution of debris in Hessbreen is controlled strongly by the development of some of these structures. Angular supraglacial debris is intimately associated with stratification, while basal debris is lifted to en- and supraglacial positions in association with thrusting.