The Flims rockslide/rock avalanche (FRRA) is the largest long runout landslide in Europe. This event provides a unique opportunity to study the pre-failure and failure behavior of a large rock slope, as both the source zone and deposit of this event are accessible. In this study, we perform engineering geological and geomorphic field mapping as well as stability and runout modeling in order to explore the preconditioning and triggering factors that resulted in failure of this event, and to infer the mechanisms that governed its runout. By combining these analyses, we qualitatively comment on the mechanisms that lead to the transition from a rockslide to a long runout, catastrophic rock avalanche. Our engineering geological and geomorphic field mapping has revealed that the FRRA failed along a sliding zone that features numerous, large scale steps. Previous work at the site, as well as new analysis of thin sections, has revealed the presence of marl-like layers within the failed stratigraphic unit. Our stability analysis shows that the presence of low strength layers at the depth of the rupture surface is required for failure to initiate, and that failure could be triggered either by strong seismic shaking, elevated pore-water pressures, or a combination of both. The results of the runout analysis show that this event likely remained coherent for a large portion of its motion, and that liquefaction of alluvial sediments at the toe of the slope may have enhanced the runout distance of this rock avalanche. Combining the mapping, stability and runout modeling has shown that the basal shear strength required for the runout analysis is ∼6°–10° lower than that back-analyzed for the stability of this event. Thus, a mechanism to reduce strength along the rupture surface immediately following the initial instability was required for catastrophic failure of this event. This mechanism is poorly understood at present, but is likely crucial for understanding the transition from an initially stable slope to a catastrophic, long runout rock avalanche.

Flims岩崩/岩石雪崩（FRRA）是欧洲最大的长跳动滑坡。该事件为研究大型岩石边坡的破坏前和破坏行为提供了独特的机会，因为可以访问该事件的源区和沉积物。在这项研究中，我们执行工程地质和地貌场制图以及稳定性和跳动模型，以探究导致该事件失败的预处理和触发因素，并推断出控制其​​跳动的机制。通过结合这些分析，我们对导致岩石滑坡过渡到长跳动，灾难性岩石雪崩的机理进行了定性评论。我们的工程地质和地貌野外测绘表明，FRRA沿滑动区域破裂，该滑动区域具有许多大型台阶。现场的先前工作以及对薄片的新分析表明，在失败的地层单元中存在类似泥灰岩的层。我们的稳定性分析表明，破裂开始时需要在破裂表面深度处存在低强度层，并且破裂可能由强烈的地震振动，升高的孔隙水压力或两者结合触发。跳动分析的结果表明，该事件在其大部分运动中可能保持连贯性，并且在坡脚趾处冲积沉积物的液化可能增加了该岩石雪崩的跳动距离。结合映射，稳定性和跳动模型表明，跳动分析所需的基础抗剪强度比对该事件的稳定性反演的基础抗剪强度低约6°–10°。因此，对于这种事件的灾难性失败，需要一种机制来在初始不稳定性之后立即沿断裂面降低强度。目前尚不清楚这种机理，但对于理解从最初稳定的坡度到灾难性的长跳动岩石雪崩的过渡可能至关重要。