Pebbly versus bouldery rock glaciers: Morphology, structure and processes
Pebbly versus bouldery rock glaciers: Morphology, structure and processes
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DOI：
10.1016/j.geomorph.2005.07.015
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发表时间：
2006-02
期刊：
影响因子：
3.9
通讯作者：
Atsushi Ikeda;N. Matsuoka
中科院分区：
文献类型：
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作者：
Atsushi Ikeda;N. Matsuoka
岩壁地质的差异导致了两种类型的岩石冰川：一种是巨砾岩石冰川，其活动层由来自结晶岩石和块状石灰石的无基质巨砾组成;另一种是卵石岩石冰川，由来自阻力较小的页岩和板状石灰石的基质支撑碎片组成。这种物质成分控制着负责两种岩石冰川的形状、大小和内部结构的运输过程。本文根据测绘、地质和地貌特征描述、地层学直接观察和内部结构的地球物理探测，比较了控制瑞士阿尔卑斯山两种类型地貌和结构的主要过程。在瑞士阿尔卑斯山，卵石冰川与巨石冰川的区别在于b轴平均直径为15-20厘米的碎屑大小。前者由小规模的落石、泥石流和泥石流补给，而后者主要来自大型落石。卵石冰川通常比巨砾冰川小（长度小于200米），因为阻力较小的源岩墙（高度小于50米）的小暴露强烈限制了碎片的供应。因此，多卵石的岩石冰川通常终止于山谷边坡内，而许多巨石冰川则延伸到谷底。卵石冰川的位置导致了低的前坡（≤20 m）和缺乏横向脊沟地形，因为缺乏压缩流。坑-井地层和低直流电阻率（<10 kΩm）表明，在含砾岩石冰川中的冰胶结或轻微过饱和的永久冻土，这可能源于地下水冻结。相比之下，在巨石冰川中，由高直流电阻率（>100 kΩm）表示的高度冰过饱和结构似乎起源于被大型源岩壁的大型落石沉积物掩埋的雪岸。
Differences in rockwall geology cause two types of rock glaciers: a bouldery rock glacier, having the active layer composed of matrix-free boulders derived from crystalline rocks and massive limestone; and a pebbly rock glacier, consisting of matrix-supported debris derived from less resistant shale and platy limestone. Such material composition controls transport processes responsible for the shape, size and internal structure of the two types of rock glaciers. This paper compares the major processes controlling the morphology and structure of the two types in the Swiss Alps, based on mapping, description of geological and morphological characteristics, direct observation of stratigraphy and geophysical soundings of internal structure. In the Swiss Alps, pebbly rock glaciers are distinguished from bouldery rock glaciers by the clast size of 15–20 cm in the mean b-axis diameter. The former are fed by small-scale rockfalls, debris flows and solifluction, whereas the latter mainly originate from large rockfalls. Pebbly rock glaciers are generally smaller (<200 m in length) than bouldery rock glaciers, because the small exposure of the less resistant source rockwall (<50 m in height) strongly constrains debris supply. As a result, pebbly rock glaciers usually terminate within a valley-side slope, whereas many bouldery rock glaciers extend into the valley bottom. The location of pebbly rock glaciers results in the low frontal slope (≤20 m) and the lack of transverse ridge-furrow topography, because of the lack of compressive flow. The pit-borehole stratigraphy and low DC resistivities (<10 kΩm) indicate ice-cemented or slightly supersaturated permafrost in the pebbly rock glaciers, which presumably originates from groundwater freezing. In contrast, highly ice-supersaturated structure indicated by high DC resistivities (>100 kΩm) in bouldery rock glaciers appears to originate from snow banks buried with deposits of large rockfalls from the large source rockwall.