Cold-based Glaciers in the Western Dry Valleys of Antarctica: Terrestrial Landforms and Martian Analogs:

Introduction: Basal-ice and surface-ice temperatures are key parameters governing the style of glacial erosion and deposition. Temperate glaciers contain basal ice at the pressure-melting point (wet-based) and commonly exhibit extensive areas of surface melting. Such conditions foster basal plucking and abrasion, as well as deposition of thick matrix-supported drift sheets, moraines, and glacio-fluvial outwash. Polar glaciers include those in which the basal ice remains below the pressure-melting point (cold-based) and, in extreme cases like those in the western Dry Valleys region of Antarctica, lack surface melting zones. These conditions inhibit significant glacial erosion and deposition. An intermediate classification of subpolar glaciers includes those with wet-based interiors and cold-based margins. Results from our field-based research in Antarctica show that ancient landscapes are preserved beneath cold-based glacier ice. These results, along with new insights from quantitative measurements of glacial abrasion [e.g., 1], have prompted us to re-evaluate some Martian landforms in terms of glacial processes. As background, we here summarize the formation of drop moraines, sublimation tills, and rock glacier deposits associated with cold-based glaciers in the Dry Valleys of Antarctica, and then [2] outline the case for similar glacial landforms along the western flanks of the Tharsis Montes. Background: Basal sliding, basal entrainment, and transport of basal debris towards the glacier base are three fundamental requirements for significant glacier erosion. Basal sliding requires subglacial meltwater, a property controlled largely by the thermal regime of the glacier. At the base of wet-based glaciers, debris is entrained chiefly through regelation, a process whereby basal meltwater is frozen onto the glacier base. Regelation normally occurs where the basal-ice temperature fluctuates about the pressure-melting point. In such cases, small bedrock obstacles yield pressure variations that induce basal-ice melting and refreezing. Refreezing of " dirty " meltwater entrains basal debris. At sites of persistent pressure melting, the continued downward transport of basal debris towards the bedrock interface results in elevated rates of bedrock erosion. Such processes result in overdeepened basins found commonly beneath cirque and valley glaciers. Although simplified, the above represents the classic scenario for wet-based, subglacial erosion [3-7]. Recent studies show that some basal debris may also be entrained beneath cold-based ice [8]. Debris may be entrained through rotation of loose bedrock by glacier flow [6] or by freezing of interfacial meltwater films (<<1 mm thick) at subfreezing temperatures [1, 9]. Theoretical and empirical studies show that liquid water at the base of glaciers …