High resolution profiles of arctic under-ice topography were measured near Ice Island T-3, about 600 kilometers from the pole. A high frequency, narrow beam, profiling sonar carried by an unmanned, torpedo-like research submersible provided an ice elevation measurement each 38 cm along a guided path beneath the ice. Selected profiles that show normal, oblique, and nearly parallel traverses of pressure ridge keels are shown. Pressure ridges are shown to have block sizes of the dimensions of the parent ice sheet. The ridge keels have not consolidated into a homogeneous mass but are replete with large voids and niches, and individual blocks are clearly identified. These properties were found on new, first-year ridges and on a 4 year old sheer ridge that was formed in ice about 5 meters thick. There is evidence that consolidation of the ridges to depths of the parent ice sheet is rapid. Little evidence of keel erosion is observed. (Author)