Geophysics and Hydrodynamics
Experimental and theoretical investigations of the generation of edge waves along a beach in the presence of gravity waves with crests parallel to the beach are presented. Subharmonic, resonant edge-wave generation is dependent on the beach slope and the period and amplitude of the primary wave. A simple, theoretical inviscid model which invokes the shallow-water approximation is studied. A standing wave with crests parallel to the coast and an edge-wave perturbation give rise to a Hill equation. Approximate determination of the stability properties indicates features similar to those observed in the experiments.
Glacial lakes occupied many valleys in southern British Columbia during retreat of Fraser Glaciation ice. The strandline deformation that has taken place in response to removal of the ice load provides a clue to the flexural properties of the lithosphere. Surfaces fitted to four strandlines of former glacial lakes are tilted from 2.5 to 1.6 m per km, with the best documented section of strandline having a tilt of 1.8 m per km for an average slope of 0.0018. The Algonquin strandline, one of the most strongly developed proglacial strandlines of the Great Lakes area has an average slope of 0.0010. The wavelength of flexure for the Algonquin strandline is 2 π 180 km, and the indicated lithospheric thickness is about 110 km. If the Cordilleran ice load were the same as the Laurentide load, which caused deformation of the Algonquin strandline, a wavelength of flexure of 2 π 100 km and a lithospheric thickness of about 50 km would be required to explain the greater Cordilleran deformation. But the Cordilleran ice load was probably only half that of the Laurentide area; so the lithosphere of the southern Canadian Cordillera apparently has a flexural parameter of about 50 km and a thickness of about 20 km.