Climate eff ects rela ng to air temperature, radia on, snow cover, and rainfall combine with thaw and infi ltra on processes to cause changes in the thermal response and associated creep deforma ons in rock glaciers, which are the geomorphological expression of Alpine permafrost. The annual surface creep of some rock glaciers has accelerated recently by an order of magnitude. A mul disciplinary fi eld study links characteriza on, monitoring, and modeling for such a rock glacier in the Turtmann valley in Switzerland. The fi rst phase consisted of characteriza on using seismic refrac on and ground-penetra ng radar (GPR), as well as borehole informa on and monitoring of meteorological, hydrothermal, and geotechnical variables over 2 yr. The ground model confi rmed the heterogeneity of the internal structure, with rock glacier topography aff ec ng the thermal distribu on in boreholes and seepage fl ows from tracer tests at between 10 and 40 m h −1 . Temperatures were generally warmer than −0.25°C in the permafrost zone, with some variability in terms of thermal degrada on of some layers to 0°C and an ac ve layer of about 3 to 5 m depth. Unique internal shear movements were measured by an automa c inclinometer, which indicated downslope creep rates in the shear zone and at the surface of about 2.4 and 3.2 m yr −1 respec vely, which could not be directly linked to temperature at the same depth. These rock glaciers have poten al for future instability, which could damage infrastructure in the valley below. It is essen al to understand why they have accelerated over the past decade through the complex interac ons that have controlled the thermo-hydromechanical response.

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To forecast rock glacier movements, it is necessary to have dependable information on their internal structures and physical properties. A first attempt to expand our knowledge of a rock glacier in the Swiss Alps involved acquiring ground-based ground-penetrating radar (GPR) data along numerous profiles using different acquisition systems and antennae with different nominal frequencies. Images derived from these ground-based data were inconsistent and unreliable. For our second attempt, we recorded GPR data using a helicopter-mounted system. The helicopter GPR sections were surprisingly good, with consistent images along adjacent and intersecting profiles. Internal shear horizons, ice-rich and ice-poor regions and the bedrock interface were well delineated on the helicopter GPR images. Besides providing excellent-quality images, the helicopter GPR system allowed areas of the rock glacier to be surveyed that would have been difficult or impossible to access for a ground-based study. Because near-surface heterogeneity does not seem to have a major effect on helicopter GPR data acquired across a rugged rock glacier, we suggest that helicopter GPR surveying might be useful for investigating many terrains covered by heterogeneous loose material, including debris avalanches, scree slopes and rockfalls.

We have performed a multidisciplinary geophysical survey combined with geotechnical investigations over a degrading alpine rock glacier. A dense grid of helicopter-borne ground-penetrating radar data allowed the 3D shape of the bedrock topography and the gross transition from ice-rich to ice-poor parts of the rock glacier to be delineated. The bedrock topography served as a 2D structural constraint for tomographic inversions of seismic and geoelectric data acquired on coincident profiles parallel and perpendicular to the rock glacier flow direction. These profile data were complemented by a small 3D geoelectric tomography experiment. Only a combined interpretation of all the results allowed reliable and unambiguous interpretation of the tomograms. We could distinguish between the active layer, bedrock, ice-bearing rock glacier material, and degraded permafrost within the rock glacier. The latter could be further distinguished in areas where the ice must have melted only recently, and regions that had degraded some time ago. Additionally, high-resolution cross-hole radar tomography, performed in an area of opening crevices, allowed small-scale structures to be resolved, which were indicative of the dominant deformation mechanisms style of the rock glacier. The success of our study was primarily based on the availability of 3D data sets that allowed important structures to be traced over larger areas and the integrated interpretation of several data types. We have identified the internal structure of the rock glacier to be surprisingly heterogeneous with several small-scale features that were judged to be critical for assessing its stability. This underpinned the need for comprehensive 3D structural investigations to augment geotechnical measurements linearly with inclinometers or at points in boreholes.

Mountainous locations and steep rugged surfaces covered by boulders and other loose debris are the main reasons why rock glaciers are among the most challenging geological features to investigate using ground‐based geophysical methods. Consequently, geophysical surveys of rock glaciers have only ever involved recording data along sparse lines. To address this issue, we acquired quasi‐3‐D ground‐penetrating radar (GPR) data across a rock glacier in the Swiss Alps using a helicopter‐mounted system. Our interpretation of the derived GPR images constrained by borehole information results in a novel “thin‐skinned” rock glacier model that explains a concentration of deformation across a principal shear zone (décollement) and faults across which rock glacier lobes are juxtaposed. The new model may be applicable to many rock glaciers worldwide. We suggest that the helicopter GPR method may be useful for 3‐D surveying numerous other difficult‐to‐access mountainous terrains.