Supraglacial landslides

Rock avalanches on glaciers are becoming increasingly common due to glacier debuttressing of valley walls, and thaw of alpine permafrost. Previous authors have described glacier surges resulting from large rock avalanches onto glacier surfaces, but no mechanism had been proposed. I combined field surveying with leading-edge remote sensing techniques and numerical modeling to quantify the effect of large landslides on glacier behaviour.

We determined the velocities of Black Rapids Glacier before and after landslide deposition in 2002 by using a combination of ERS-1/ERS-2 tandem, RADARSAT-1, and ALOS PALSAR synthetic aperture radar (InSAR) data. We found that within a few years of landslide deposition, the velocity of the debris-covered area was uniform, resulting from a reversal of the velocity gradient. A full-Stokes numerical ice flow model demonstrated that a reduction in surface ablation caused by the landslide debris decreased the surface slope of the glacier and caused the velocity gradient to reverse.

InSAR (synthetic aperture radar interferometry) velocity map, Black Rapids Glacier, Alaska
GIS-based analysis of boulder sizes, Black Rapids Glacier, Alaska
Measuring rock fabric on massive landslides on Black Rapids Glacier, Alaska
Geologist Denny Capps, Ph.D. stands on the debris of a rock avalanche on Jarvis Glacier, British Columbia

The sedimentology of rock avalanches has been described qualitatively but quantitative measures have been lacking, largely due to the massive scale of the deposits and the hazards associated with field mapping. I developed a method for analysizing these deposits by combining field mapping with air photo analysis in a GIS. In so doing, I produced the first quantitative maps of rock avalanche sedimentology. From high-resolution orthophotos, I digitized ~265,000 boulders within the deposits of three rock avalanches on Black Rapids Glacier, Alaska, and one at Frank Slide, Alberta, and calculated a variety of spatial statistics to quantify the observed patterns.

Dufresne, A., Geertsema, M., Shugar, D.H.,…ΩBonno, D., and 10 other authors. 2018. Sedimentology and geomorphology of a large tsunamigenic landslide, Taan Fiord, AlaskaSedimentary Geology, 364: 302-318. DOI: 10.1016/j.sedgeo.2017.10.004

Deline, P., Hewitt, K., Reznichenko, N., and Shugar, D.H. 2014. Rock avalanches onto glaciers. In: Davies, T. R. (Ed) Landslide Hazards and Disasters. Elsevier, pp. 263-319. DOI: 10.1016/B978-0-12-396452-6.00009-4

Shugar, D.H., Clague, J.J., Giardino, M., 2013. A quantitative assessment of the sedimentology and geomorphology of rock avalanche deposits, In: Landslide Science and Practice, Vol 4: Global Environmental Change. Springer-Verlag, pp. 321-326. DOI: 10.1007/978-3-642-31337-0_41

Shugar, D.H., Rabus, B.T., Clague, J.J., Capps, D.M., 2012. The response of Black Rapids Glacier, Alaska, to the Denali earthquake rock avalanches. J. Geophys. Res. 117, doi:10.1029/2011jf002011. DOI: 10.1029/2011JF002011

Shugar, D.H., Clague, J.J., 2011. The sedimentology and geomorphology of rock avalanche deposits on glaciers. Sedimentology 58, 1762-1783. DOI: 10.1111/j.1365-3091.2011.01238.x