Abstract Valley glaciers have traditionally been expected to significantly influence the stability and movement rates of adjacent paraglacial landslides. However, detailed studies related to the mechanical and displacement interactions between glacier ice and unstable rock slopes are very rare. Here we present a detailed in-situ investigation of the spatial variations of the displacement field of the Great Aletsch Glacier in the surroundings of a large active instability, i.e., the Moosfluh Landslide, a Deep-Seated Gravitational Slope Deformation, with superimposed large (1–5 million m3) secondary rockslides formed during fall 2016. We performed repeat UAV-based photogrammetric surveys during ~3 days (74 h) and applied Digital Image Correlation techniques to record high-resolution surface displacement vector fields of the landslide, stable slopes and adjacent glacier. Our results show that the secondary rockslide adjacent to the glacier is composed of two parts of 1.5 and 2.8 million m3 volume respectively, showing significant differences in mean displacement velocities (0.4 and 0.9 m in 74 h respectively, excluding rapid movements from detached blocks). Both rockslide compartments induce clear deflections of the glacier flow field, moving with a maximum velocity of about 0.3 to 0.4 m in 74 h. This influence is highest near the ice-contact boundary and decreases within a distance of about 100–200 m from the rock slope instability. We investigate the viscous forces at the landslide/glacier contact using a straightforward analytical model for an incompressible rockslide block sliding along a planar, cohesionless surface into ice. These forces are then applied to a slope stability model based on the limit equilibrium concept, representing the real geometry at the interface boundary to quantitatively explore the true buttressing effects of valley glaciers on an already moving slope instability. We show that the viscous ice deformation plays an important role in mediating the displacement velocities of landslides in unstable conditions, while, on the other hand, the slope support from the valley glacier has very little influence on the stability of the investigated rockslides. As most valley glaciers are currently strongly retreating due to global warming, uncovering significant numbers of pre-LIA slope instabilities, this detailed investigation provides important hints on their potential displacement behavior. Understanding the factors controlling landslide velocity is of great importance for hazard analyses and early warning. Hence, this study has implications beyond academic interest, e.g., for the planning and operation of alpine infrastructure, such as cable cars or hydropower systems.

中文翻译：

---

活动岩石滑坡-冰川相互作用的监测和分析（Moosfluh，瑞士）

摘要 传统上，人们预计河谷冰川会显着影响相邻冰河滑坡的稳定性和运动速率。然而，关于冰川冰和不稳定岩石斜坡之间的机械和位移相互作用的详细研究非常罕见。在这里，我们对大阿莱奇冰川在大型活动不稳定环境中的位移场空间变化进行了详细的原位调查，即 Moosfluh 滑坡，一种深层重力斜坡变形，叠加了大 (1 –500 万立方米）次生岩崩在 2016 年秋季形成。我们在大约 3 天（74 小时）内重复进行了基于无人机的摄影测量调查，并应用数字图像相关技术记录了滑坡的高分辨率表面位移矢量场，稳定的斜坡和相邻的冰川。我们的结果表明，与冰川相邻的次生滑坡由体积分别为 1.5 和 280 万立方米的两部分组成，显示出平均位移速度的显着差异（74 小时内分别为 0.4 和 0.9 米，不包括脱离块体的快速运动）。两个岩石滑坡隔间都会引起冰川流场的明显偏转，在 74 小时内以大约 0.3 到 0.4 m 的最大速度移动。这种影响在冰接触边界附近最大，并在距岩石边坡失稳约 100-200 m 的距离内减弱。我们使用一个简单的分析模型来研究滑坡/冰川接触处的粘性力，用于不可压缩的滑坡块沿着平坦的、无凝聚力的表面滑入冰中。然后将这些力应用于基于极限平衡概念的斜坡稳定性模型，代表界面边界处的真实几何形状，以定量探索山谷冰川对已经移动的斜坡不稳定性的真实支撑效应。我们表明，粘性冰变形在不稳定条件下对滑坡位移速度的调节起着重要作用，而另一方面，山谷冰川的斜坡支撑对所研究的滑坡稳定性影响很小。由于全球变暖，大多数山谷冰川目前正在强烈退缩，揭示了大量的前 LIA 斜坡不稳定性，这项详细的调查提供了关于它们潜在位移行为的重要提示。了解控制滑坡速度的因素对于灾害分析和预警非常重要。因此，这项研究的意义超出了学术兴趣，例如，对于高山基础设施的规划和运营，如缆车或水力发电系统。