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Rock glaciers Gruben, Muragl and Murtel, Switzerland: Area-wide flow fields, Version 1

Besides their thermal and mechanical properties, rock glaciers are essentially defined by their kinematics. Knowledge of the permafrost flow field provides important information about the origin, morphology, development, dynamics and internal structure of creeping mountain permafrost. Monitoring permafrost behavior helps detecting climate signals.

Aerial photogrammetry was used for determining digital terrain models (DTM) with high resolution. The differences of multitemporal DTMs of a rock glacier provide the vertical changes of the permafrost surface. Horizontal surface displacements were obtained by simultaneously comparing two aerial photographs taken at different times and from different positions (Kaeaeb 1996a,b; Kaeaeb et al.1998). Repeated overridings by the nearby glacier affected the upper part of the Gruben rock glacier, Wallis. Compared to the lower, periglacial part of the rock glacier the higher surface lowering rates of the debris-covered dead ice remains indicate the dead ice being out of equilibrium. Due to different internal structure and different slopes, horizontal surface velocities show different creep directions as well as different creep rates. The rock glacier advances by about 12 cm/a. A 25-year time series of photogrammetrical monitoring (1970-1995) documents the temporal variations of surface kinematics of the rock glacier (Kaeaeb et al. 1998a). Surface kinematics of Muragl rock glacier (Upper Engadin) over the period from 1981 to 1994 reveal this rock glacier to be a complex system of several individual streams. Changes in elevation show a pattern of zones of surface heave and subsidence in the range of +- 10 cm/a. The rock glacier advances by about 5 cm/a (Kaeaeb 1998). The velocity field 1987-1996 at the surface of Murtel rock glacier, Upper Engadin, points to two dynamically different parts of the creeping permafrost-- (1) high activity and transverse ridges in the inner part and (2) lower activity at the left and right margins. The ridges are advected down stream with a velocity approximately equal to the surface velocity. Stream lines can be interpolated from the surface velocity field. The curvature of the isochrones on Murtel rock glacier is similar to the curvature of the transverse ridges, which suggests slow changes in the flow field (Kaeaeb 1998, Kaeaeb et al. 1998b). These data are presented on the CAPS Version 1.0 CD-ROM, June 1998.

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