Rock avalanches on glaciers

• Main Author: Shugar, Daniel
• Format: Thesis
• Language: unknown
• Published: 2011
• Subjects: glacier; glaciers; Alaska
• Online Access: http://summit.sfu.ca/item/11909

This thesis examines relations between rock avalanches and the glaciers on which they are deposited. I have attempted to understand a geophysical phenomenon from two viewpoints: sedimentology and glaciology. The contributions are both methodological, and practical. I have used a GIS to quantify debris sheet geomorphology. A thorough characterization of rock avalanche debris is a necessary step in understanding the flow mechanics of large landslide. I have also developed a technique for solving radar interferometry phase unwrapping problems. A digital elevation model created using this technique is used to quantify the velocity of a glacier prior to its disturbance by landslides. Three debris sheets on Black Rapids Glacier, Alaska, have coarse blocky rims. Longitudinal flowbands in these debris sheets, as well as in a debris sheet deposited on Sherman Glacier, Alaska, separate bands of different block size. Elongated blocks are parallel to flow, except at the perimeter of the debris sheets, where they are aligned nearly perpendicular to flow. Blocks on Sherman Glacier have been reoriented by glacier flow since the landslide in 1964. The matrix of all four debris sheets does not systematically change with depth or distance from the source. However, Sherman Glacier debris has become coarser due to weathering. Black Rapids Glacier surged in 1936-1937. Between 1949 and 1995, the glacier gradually returned to a pre-surge hypsometry. Maximum elevation changes along the glacier centerline in the ablation and accumulation areas, are, respectively, -249 m (-5.4 m a-1) and +63 m (+1.4 m a-1). Centerline thickening of +62 m (+1.4 m a-1), just above the Loket tributary in the upper part of the ablation zone, indicates dynamic thickening following the surge. The response of Black Rapids Glacier to the rock avalanches is spatially and temporally complex. Increases in measured and modelled surface velocity across the debris sheets are much greater than velocities observed higher on the glacier. The velocity recorded at the downglacier margin of the debris doubled between 2002 and 2004, resulting in a reversed velocity gradient. The changes in ice dynamics are related to the landslides through the effect of debris insulation on mass balance.