Mechanisms of debris supply onto rock glaciers

最近的全球变暖导致中纬度高山的岩石冰川融化，可能引发岩石雪崩和泥石流。这项研究的目的是根据碎屑产生过程来模拟岩石冰川动力学。瑞士阿尔卑斯山的野外观测包括：(1)自动监测岩石节理扩展和岩壁上的岩石温度；(2)测量落石碎片的大小和体积；(3)岩石碎片成分的纵向变化；(4)岩石冰川结构的直流电阻率层析成像。(1)季节性冻结使岩石节理增大，随后的融化触发巨石落石，这意味着落石碎石的体积主要取决于最大冻融深度。(2)倾倒的巨石可堆积在距骨坡外，最终形成覆盖在冻土蠕变的下部冻结碎屑层上的上部开挖块状岩层。这种落差分类导致了双层结构。(3)近期气候变暖加速了位于山体多年冻土带下限附近的许多岩石冰川的运动。然而，这反过来又减少了碎屑层的厚度和表面坡度，最终使岩石冰川失活。岩石冰川运动也表现出显著的年际变异性。最后，基于岩壁碎屑产生率和岩石冰川三维运动的现场数据，提出了一个当代岩石冰川碎屑收支模型。

Recent global warming has caused melting of rock glaciers in mid-latitude high mountains, possibly triggering rock avalanches and debris flows. This research aims at modeling rock glacier dynamics in terms of debris production processes. Field observations in the Swiss Alps involve : (1) automated monitoring of rock joint propagation and rock temperature on rockwalls ; (2) measurements of the size and volume of rockfall debris ; (3) longitudinal variation in the composition of rock debris ; and (4) DC resistivity tomography on rock glacier structure.The research provided the following outcomes. (1) Seasonal freezing enlarges rock joints and subsequent thawing triggers boulder falls, which means that the volume of rockfall debris depends mainly on the maximum freeze-thaw depth. (2) Fallen large boulders can deposit beyond the talus slope, which eventually develop the upper open-work blocky layer overlying the lower frozen debris layer with permafrost creep. Such fall sorting results in the two-layer structure. (3) Recent warming has accelerated the movement of many rock glaciers located near the lower limit of the mountain permafrost belt. However, this in turn decreases the thickness of the debris layer and surface gradient, eventually inactivating the rock glaciers. The rock glacier movement also shows significant inter-year variability in response to snow conditions.Finally, a model of the contemporary debris budget in rock glaciers was proposed on the basis of the field data on the rate of debris production from rockwalls and the tree-dimensional movement of rock glaciers.