Abstract

Ribbed moraines are large (up to 16 km long) ridges of sediment produced transverseto ice flow direction that formed widely beneath palaeo-ice sheets. Since ice sheetstability is sensitive to conditions operating at the bed, an understanding of ribbedmoraine genesis will provide critical information on ice sheet dynamics. Currently, thereis no consensus on ribbed moraine formation and various competing hypotheses havebeen presented to account for their genesis. Only one of these theories has beendeveloped into a physically based numerical model that quantitatively describes ribbedmoraine formation. This theory, known as the Bed Ribbing Instability Explanation(BRIE), argues that ribbed moraines are produced by a naturally arising instability in thecoupled flow of ice and till. BRIE demonstrates that transverse subglacial ridges (i.e.,ribbed moraine) spontaneously grow under certain parameter combinations, and itpredicts their wavelength (spacing between ridges). The model represents a significantadvance because it is the first time a theory of subglacial bedform generation has beendeveloped to make quantitative predictions which can be formally tested. This paperdiscusses the types of tests that are currently possible and reports the results from the firsttesting of BRIE. This analysis centers on the ability of BRIE to predict the primarycharacteristics of ribbed moraine, which are patterning and wavelength. Results show thatBRIE successfully predicts the correct ribbed moraine pattern and appropriate wavelengths.The tests fail to falsify the model, and it is concluded that BRIE remains a viableexplanation of ribbed moraine formation.