A Quantitative Assessment of the Sedimentology and Geomorphology of Rock Avalanche Deposits

摘要

We use digital photo-sieving and spatial statistics to quantify the debris of three landslides on Black Rapids Glacier, Alaska, and the non-glacial Frank Slide, Alberta. The debris sheets on Black Rapids Glacier have clusters of large blocks in parts of their distal rims; small clusters of large blocks also occur elsewhere, including the proximal side of a high medial moraine. Longitudinal flowbands formed by shearing within the debris and marked by different block sizes characterize all three Black Rapids debris sheets. In contrast, no flowbands are evident on the Frank Slide debris sheet. Especially large blocks form a conspicuous cluster in the middle of the Frank Slide debris sheet. The distal edge is composed of small blocks. The presence of many of the largest blocks at the peripheries of the three Black Rapids Glacier debris sheets indicates that the landslides spread without confinement. The lack of a coarse distal rim at Frank may indicate that the irregular topography over which the debris traveled influenced the distribution of the largest blocks. Patches of different types of carbonate rock within the Frank Slide debris sheet indicate that source-zone stratigraphy is preserved within the debris sheet. Differences among the studied debris sheets reflect different paths and substrates over which the landslides traveled: unconfined spreading and continuous, progressive thinning of debris traversing a relatively flat surface of snow and ice at Black Rapids Glacier; and topography-controlled spreading over an irregular rising and vegetated surface at Frank.