The budget and effect of superglacial debris on Eliot Glacier, Mount Hood, Oregon

Because superglacial debris (SGD) can significantly reduce glacial ablation, SGD budgets, necessary for alpine erosion estimates, can affect glacier-climate relationships. At a temperate valley glacier located on an Oregon Cascade Range stratovolcano, the distribution, thickness, and sedimentology of SGD were studied in relation to ice mass balance, surface velocity, and topography of the glacier ablation area during 1984-1989. Lateral moraines were studied for past glacier sediment flux and response to climate change.; Sandy diamictons cover 60% of the ablation area and thicken downglacier to 1-2m thick. SGD largely melts out of englacial position and originates as rockfall from slopes adjoining the accumulation area. The ablation rate of debris-covered ice is inversely related to SGD thickness for debris {dollar}>{dollar}1cm thick, and is consistent with thermal conduction as the predominant energy flux through SGD. The inverse relation provides a basis for analysis of debris cover development. The downglacier increase of SGD thickness along a media moraine, assuming steady surface velocity and debris distribution, implies volumetric englacial debris concentrations of 0.0004-0.002, and a mean erosion rate of {dollar}sim{dollar}1mm/a of the summit headwall of Mount Hood. Proglacial suspended sediment flux dominated by silt during summer 1988 is equivalent to {dollar}sim{dollar}1mm/a of glacier bed erosion.; Information on soil development, tephra stratigraphy and moraine morphology constrains periods of left lateral moraine construction to late Pleistocene, to early Neoglacial advances preceding ash deposition at {dollar}sim{dollar}1500-1800 and {dollar}sim{dollar}450(?) years ago, and to the Little Ice Age (LIA). Sediment flux required for LIA moraine construction indicates significant SGD during that time, and requires no more than 50 m of snowline depression relative to present. Lower Eliot Glacier thinned at an average rate of 0.2m/a since the LIA, compared to 0.8m/a during 1984-1989.; Eliot Glacier presently transports and stores high-level debris at lower rates than were required for lateral moraine construction. Paleoglacial reconstructions that do not recognize lateral moraine evidence for significant superglacial debris overestimate associated past climate change.