| الوصف: |
Improvements in the resolution of seafloor mapping techniques have revealed extremely regular, sub-meter scale ridge landforms produced by the tidal flexure of ice-shelf grounding lines as they retreated very rapidly (i.e., at rates of several kilometres per year). Guided by such novel seafloor observations from Thwaites Glacier, West Antarctica, we present three mathematical models for the formation of these corrugation ridges at a tidally migrating grounding line (that is retreating at a constant rate) where each ridge is formed by either constant till flux to the grounding line, till extrusion from the grounding line, or by the resuspension and transport of grains from the tidal cavity. We find that both till extrusion (squeezing out till like toothpaste as the ice sheet re-settles on the seafloor), and resuspension and transport of material from the grounding-zone bed can qualitatively reproduce regular, delicate ridges at a retreating grounding line as described from seafloor observations. By considering the known properties of subglacial sediments we agree with existing schematic models that the most likely mechanism for ridge formation is till extrusion at each low-tide position, essentially preserving an imprint of the ice-sheet grounding line as it retreated. However, when realistic (shallow) bedslopes are used in the simulations ridges start to overprint one another suggesting that, to preserve the regular ridges that have been observed, grounding line retreat rates (driven by dynamic thinning?) may be even higher than previously thought. |
