PERMAFROST AND ROCK SLOPE STABILITY (INVITED)

An increasing number of rockfalls and rock slope failures from permafrost-affected rock faces have been reported in the last 20 years. However, rock slopes are complex systems with enormous memory effects, very long response times and a high level of spatial complexity on all scales. It is, thus, difficult to reveal systematic patterns of how permafrost rocks react to climate change from the short time scale of field observation.

Here, we turn the problem upside down and look at systemic mechanical changes of bedrock with degrading permafrost. Warming frozen bedrock induces fundamental changes in rock- and ice-mechanical properties even well before melting the systems. From a rock mechanical point of view, warming significantly decreases compressive and tensile strength as well as fracture toughness of porous frozen rocks. From an ice-mechanical point of view, warming permafrost affects creep and fracture of ice in fractures and along rock-ice interfaces. We combine these aspects to a rock-ice mechanical model, which can explain anticipated temporal and spatial patterns as well susceptible magnitudes of rock slope failure following climate change.

In the laboratory, we have we have started to systematically analyze the mechanical behavior of frozen and thawed rocks to proof the assumptions of the rock-ice mechanical model. Hereby we focus on changes in compressive and tensile strength, elastic properties, p- and s-wave propagation and electrical properties. To approach natural conditions we incorporate effects deriving from anisotropy and scale effects. In the field, we instrumented well-constrained rock instabilities with degrading permafrost to derive high-precision kinematic data and alongside with mechanical data of forcing parameters such cryostatic pressures. Hereby, we can distinguish typical mechanical regimes that we know from laboratory measurements and investigate the effectiveness of different processes incorporated in the rock-ice mechanical model.

Here, we develop a simple rock ice-mechanical model that is capable of explaining spatial and temporal patters of rock instability in degrading permafrost rocks and test assumptions in the field and in the lab.