A depositional model for outwash, sediment sources, and hydrologic characteristics, Malaspina Glacier, Alaska; a modern analog of the southeastern margin of the Laurentide ice sheet

The Malaspina Glacier on the southern coast of Alaska is a partial analog of the late Wisconsinan Laurentide Ice Sheet that occupied New England and adjacent areas. Ice lobes of the Malaspina are similar in size to end moraine lobes in southern New England and Long Island. Estimated ablation rates, surface slopes, and meltwater discharge per unit of surface area for the Laurentide Ice Sheet are comparable to measured ablation rates, surface slopes, and meltwater discharge rates for the Malaspina Glacier. Meltwater moves from the surface of the Malaspina down-glacier and toward the bed of the glacier along intercrystalline pathways and through a series of tunnels. Regolith beneath the glacier, which is eroded and transported to the margin of the glacier by subglacial and englacial streams, is the source of essentially all fluvial and lacustrine deposits on the Malaspina Foreland. By analogy, a similar hydrologic system existed at the southeastern margin of the Laurentide Ice Sheet. Subglacial regolith, which was eroded from beneath the ice sheet by meltwater, was the source of most stratified sediment deposited in New England and adjacent areas during the late Wisconsinan. Similarly, Wisconsinan ice-contact landforms in New England were built by the same processes that are constructing landforms composed of stratified sediments in contact with the Malaspina Glacier. For the Malaspina Glacier and the Laurentide Ice Sheet, therefore, we reject the concept of the "dirt machine" by which debris near the base of the glacier is carried to the surface of the glacier along shear planes and then washed off the surface to form ice-contact stratified deposits.