Conduit Pressure Beneath Glaciers and Ice Sheets

The resistance to sliding beneath soft-bedded glaciers de5 pends on the effective stress N , which is controlled by the subglacial hy6 drological system. While large-scale water transport is primarily through 7 conduits, the effective stress profile beneath most of the glacier base is 8 expected to be controlled by seepage flows through the permeable sed9 iments. Models of the response to forced changes of the near-conduit 10 effective stress demonstrate that perturbations in N decay over a char11 acteristic lateral distance that is typically only a few times the sediment 12 thickness. This implies that only relatively small changes to the spatially 13 averaged effective stress N̄ can be produced if conduit spacing is compar14 atively large and the glacier and sediments remain in contact. To produce 15 larger changes to N̄ , it is likely that flotation must be achieved beneath a 16 significant portion of the glacier base. At higher values, spatial variations 17 in N can produce gradients in the thickness h of a fringe of ice-infiltrated 18 sediments immediately adjacent to the glacier base; this has implications 19 for the development of glacial landforms when sliding causes sediment 20