ABSTRACT Boulders in the ablation areas of Alpine valley glaciers were found to not travel along with the ice in a passive manner only. Many show an additional but smaller component of movement towards the south. We investigate this phenomenon and its governing processes using field observations and measurements from terrestrial and aerial photographs of glaciers in the Swiss Alps. We found that large boulders can migrate from their medial moraine due to cyclic formation of classical glacier tables and also a similar process that produces ice tails. The main driving factors behind boulder migration are the size (and shape) of the boulder, ablation, radiation, and surface slope. On glaciers roughly oriented to the east or west, these processes result in a sorting of boulders from the supraglacial moraine towards the southern side, i.e. towards the sun. Future studies complementing our approach using a differential global positioning system should be able to better distinguish between the velocity components of ice flow and boulder migration, determine the precise azimuth of the latter, and investigate the potential influence on photogrammetric feature tracking.

中文翻译：

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阿尔卑斯山谷冰川表面迁移的巨石

摘要 阿尔卑斯山谷冰川消融区的巨石被发现不会仅以被动方式与冰一起移动。许多显示出向南移动的额外但较小的部分。我们使用来自瑞士阿尔卑斯山冰川的地面和航空照片的实地观察和测量来研究这种现象及其控制过程。我们发现，由于经典冰川表的循环形成以及产生冰尾的类似过程，大型巨石可以从它们的内侧冰碛迁移。巨石迁移的主要驱动因素是巨石的大小（和形状）、烧蚀、辐射和表面坡度。在大致向东或向西的冰川上，这些过程导致巨石从冰上冰碛向南侧分选，即 朝向太阳。未来使用差分全球定位系统补充我们方法的研究应该能够更好地区分冰流和巨石迁移的速度分量，确定后者的精确方位角，并研究对摄影测量特征跟踪的潜在影响。