Sediment movement rates and processes on cinder cones in the maritime Subantarctic (Marion Island)

摘要

Sediment transport in the scoria areas of Marion Island is primarily the result of needle-ice-induced frost creep associated with diurnal soil frost cycles. Clasts move most rapidly in fine textured areas (532 mm a~(-1); SD 382), more slowly in stony areas (161 mm a~(-1); SD 179), and most slowly in blocky areas (26 mm a~(-1); SD 23). Movement rates increase with increasing frost susceptibility of sediments, slope angle and altitude. The heave of dowels indicates that frost heave is active in all the scoria areas examined. The depth of effective frost heave increases with increasing altitude, with frost heave being restricted to the upper 100 mm of the soil in low altitude areas (<200 m). The heave of 150 mm dowels at the higher altitude sites provides evidence for segregation ice formation at depths greater than those associated with needle ice and diurnal soil frost cycles. Vertical movement profiles show a concave downslope profile, with sediment movement rates being most rapid at the soil surface and decreasing rapidly with depth. This profile shape is typical of areas dominated by diurnal freeze-thaw cycles and needle ice. The capture of sediments moving downslope in troughs and the sampling of material lifted by needle ice, suggest that sediment transport by needle ice under present conditions is extremely effective. Observations suggest that although both fine material and clasts are transported downslope, some preferential transport of clasts occurs. Experiment results and observations of soil frost processes suggest that frost creep associated with needle ice activity is the dominant slope process in the scoria areas of Marion Island. Other slope processes such as slopewash and debris flows appear to play a relatively minor and localized role in sediment transport. It is suggested that needle ice activity is likely to be the dominant geomorphic agent in other areas of the Subantarctic with similar climatic characteristics to Marion Island.