Permafrost creep and rock glacier dynamics†
Final report of the Task Force on Permafrost Creep and Rock Glacier Dynamics. This Task Force was established in 1998 by the International Permafrost Association (IPA) and the International Commission on Snow and Ice (ICSI; now the Commission on Cryospheric Sciences, CCS) with Wilfried Haeberli and Bernard Hallet as co‐chairs in order: (1) to define the state of knowledge relevant to the flow and evolution of perennially frozen ice/rock mixtures; and (2) to provide an overview of ongoing studies that obtain quantitative information from drilling, geophysical soundings, geodetic/photogrammetric monitoring and measurements of surface conditions. For this purpose, a special half‐day workshop took place on 27 March 2001 within the framework of the First European Permafrost Conference in Rome, Italy (Rea, 2001). Further discussions followed during and after the 8th International Conference on Permafrost in Zurich (20–25 July 2003). The present contribution is based on the corresponding results and constitutes the final product of the Task Force. The following colleagues served as lead authors of the main subsections in this report: thermal conditions: Ole Humlum (surface, active layer) and Daniel Vonder Mühll (boreholes); composition: Norikazu Matsuoka (rocks) and Roger Elconin (ice); geometry/kinematics: Andreas Kääb and Viktor Kaufmann (photogrammetry, geodesy); and rheology: Sarah Springman, Lukas Arenson (mountains) and Branko Ladanyi (lowlands).
Abstract
This review paper examines thermal conditions (active layer and permafrost), internal composition (rock and ice components), kinematics and rheology of creeping perennially frozen slopes in cold mountain areas. The aim is to assemble current information about creep in permafrost and rock glaciers from diverse published sources into a single paper that will be useful in studies of the flow and deformation of subsurface ice and their surface manifestations not only on Earth, but also on Mars. Emphasis is placed on quantitative information from drilling, borehole measurements, geophysical soundings, photogrammetry, laboratory experiments, etc. It is evident that quantitative holistic treatment of permafrost creep and rock glaciers requires consideration of: (a) rock weathering, snow avalanches and rockfall, with grain‐size sorting on scree slopes; (b) freezing processes and ice formation in scree at sub‐zero temperatures containing abundant fine material as well as coarse‐grained blocks; (c) coupled thermohydro‐mechanical aspects of creep and failure processes in frozen rock debris; (d) kinematics of non‐isotropic, heterogeneous and layered, ice‐rich permafrost on slopes with long transport paths for coarse surface material from the headwall to the front and, in some cases, subsequent re‐incorporation into an advancing rock glacier causing corresponding age inversion at depth; and (e) the dynamics of rock glaciers, which include spatial and temporal variations in velocity that are manifested in the ridges, furrows and other surface structures typical of rock glaciers, as well as their down‐valley motion. Copyright © 2006 John Wiley & Sons, Ltd.
