[1] Surface movement, internal deformation, and temperature were monitored over 5 years on Büz North rock glacier, a small rock glacier located at the lower limit of the permafrost belt in the Swiss Alps. The permafrost in the rock glacier mainly consists of pebbles and cobbles filled with interstitial ice. Two inclinometers installed at 4 and 5 m depths showed fast deformation with large seasonal and interannual variations, while the permafrost temperatures remained almost at the melting point. The movement of the inclinometers coincided with changes in the surface velocities. The deformation rapidly accelerated during snowmelt periods, whereas it gradually decelerated below a dry snow cover in winter. The frozen debris was more deformable than typical glacier ice at the melting point. These phenomena suggest that the frozen debris is permeable to snowmelt water. The fast deformation should result from significant annual relocation of debris particles, which probably creates a network of air voids in the frozen debris that eventually allows water infiltration. The meltwater infiltration accelerates the deformation by reducing effective stress, resulting in the reduced strength of the frozen debris. The refreezing of the pore water, which depends on the cooling intensity in winter, decelerates the deformation. The combination of these processes controls the temporal variations in the deformation.

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[1] Six different geophysical investigations, (1) ground-penetrating radar, (2) DC resistivity sounding, (3) seismic refraction, (4) very low frequency (VHF) electromagnetic, (5) helicopter borne electromagnetic (HEM), and (6) transient electromagnetic (TEM) techniques, were employed to obtain information on the ice body properties of pingos near Fairbanks, Alaska. The surface nuclear magnetic resonance (NMR) data were also compared from similar sites near one of the study pingos. The geophysical investigations were undertaken, along with core sampling and permafrost drilling, to enable measurement of the ground temperature regime. Drilling (ground truthing) results support field geophysical investigations, and have led to the development of a technique for distinguishing massive ice and overburden material of the permafrost. The twodimensional DC resistivity sounding tomography and ground-penetrating radar profiling are useful for ice detection under heterogeneous conditions. However, the DC resistivity sounding investigation required high-quality ground contact and less area coverage. The active layer thickness and the homogeneous horizontal structure of the overburden material are important parameters influencing detection of massive ice in permafrost for most methods such as seismic, TEM, or surface NMR.

Active and inactive rock glaciers differ from relict rock glaciers in the presence of subsurface permafrost, as indicated by high seismic velocity, high DC resistivity and low bottom temperature of the winter snow cover. The lack of vegetation on the frontal slope and negative mean annual surface temperatures (MAST) distinguish active rock glaciers from inactive rock glaciers. Increasing MAST induces melting of ice‐rich permafrost, which is followed by the subsidence of rock glaciers. As a result, convex‐up transverse profiles are replaced by flat or depressed profiles. Permafrost degradation inactivates rock glaciers by decreasing shear stress, within or at the base of the deforming ice/rock mixture, causing stabilization and declination of the frontal slope. Relict rock glaciers are usually associated with soil development over the surficial clasts, which is responsible for further declination of the frontal slope and a more rounded topography. Copyright © 2002 John Wiley & Sons, Ltd.