This is an abraded rock surface overridden by the cold-based Fountain Glacier on Bylot Island.
It's argued that the rough surface and rather chaotic pattern of striae is typical of cold-based or polar glaciers -- and that the beautiful smoothed surfaces with regular and parallel striae are more typical of wet-based or warm-based glaciers. I'm not sure about that. Time is one factor, rock type is another, and sediment availability (and the occurrence of suitable "tools") is yet another. I remain to be convinced......
Smooth striated surface, Rödlöga Storskär, Stockholm Archipelago. Signs of overriding
wet-based ice?
Smoothed and striated gneiss bedrock on the west coast of Lewis, western Scotland.
The assumption is that beneath a cold-based glacier (such as those found in high latitudes) water cannot pass down to the bed from the surface, except in the immediate vicinity of the snout. So there may be an oscillating wet-based zone near the snout, moving forward and back as the snout advances or retreats, and maybe expanding and contracting seasonally as well. But the rest of the glacier -- including the accumulation area and the central "transport" section, should be cold-based and dry, with the ice either frozen to its bed or moving without any lubrication.
So the difference in rock surface effects should in theory be similar to the difference between dry sandpaper abrasion and wet sandpaper abrasion. In the latter case, as basal ice melts and lubricates the bed, not only is basal ice movement faster, but there is a continuous supply of abrasive materials as the glacier is gradually let down onto its bed.
The precise mechanics are of course seldom actually observed.......
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