Fjords form when ice sheets gouge out a valley below sea level - but what makes the ice bite so deep?
A variety of factors was thought to be behind the rapid and deep incisions made as ice sheets flow down from the mountains. For example, if the sheet moves from a region where it is frozen to the bedrock to a region where the rock surface is slightly warmer, the ice might start to slide against the rock, eroding it more rapidly.
Mark Kessler of the University of Colorado at Boulder and his colleagues now reckon the process is simpler than that. The team built a computer model of a mountain range, with saddles representing valleys cut by rivers. This showed the ice sheets that covered the mountain range moving towards the sea via the saddles with the steepest slope. Erosion by the ice made these valleys deeper and ...
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