HR: 14:20h
AN: H23H-03 INVITED    [Abstracts]
TI: Combination of Geophysical Methods for Measuring the Structure of Rock Glaciers
AU: * Ikeda, A
EM: aikeda@geoenv.tsukuba.ac.jp
AF: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan
AB: The internal structure of talus-derived rock glaciers was surveyed by a combination of electrical resistivity and refraction seismic measurements to study effects of lithological and thermal situations on the development of rock glaciers. P-wave velocity, direct current (DC) resistivity and/or year-round ground surface temperature were measured on 32 rock glaciers in the Alps and 6 rock glaciers in the Brooks Range, Alaska. In the Alps, two lithological situations were compared: one resulted in bouldery rock glaciers covered with matrix-free boulders and the other pebbly rock glaciers consisting of matrix-supported pebbles and cobbles. Different structure accompanying permafrost thawing was studied through the comparison of vegetated rock glaciers with (non- vegetated) bouldery/pebbly rock glaciers, because such vegetated rock glaciers have been regarded as relict in the Alps. In the Brooks Range located in the continuous permafrost area, bouldery rock glaciers are mostly vegetated but probably contain permafrost. The structural difference of rock glaciers between the Alps and much colder and drier Brooks Range is also discussed. In the Alps, subsurface P-wave velocity differed significantly between the bouldery/pebbly rock glaciers (>2 km/s) and the vegetated rock glaciers (<1 km/s). In addition, the bouldery/pebbly rock glaciers had lower surface temperatures than the vegetated rock glaciers. These results indicate the presence of permafrost in the former and the absence in the latter. DC resistivity differed between the bouldery (10-5000 kohmm) and pebbly (0.5-20 kohmm) rock glaciers, whereas the subsurface resistivity had similar values between the pebbly and vegetated types. The bouldery rock glaciers in the Brooks Range lacked high resistivity core (>100 kohmm). Thus, the difference in the resistivity does not reflect the ground temperature (e.g. frozen or unfrozen) but the structural difference (e.g. bouldery or pebbly). In particular, high resistivity values (>100 kohmm) in rock glaciers probably indicate highly ice-supersaturated structure. Such ice-supersaturation in bouldery rock glaciers in the Alps corresponds to the highest potential of snow burial for this type of rock glaciers, having the late-lying thick snow and large rockwalls occasionally providing rock avalanches.
DE: 0710 Periglacial processes
DE: 0722 Rock glaciers
DE: 1823 Frozen ground
DE: 1835 Hydrogeophysics
SC: Hydrology [H]
MN: 2007 Fall Meeting