Wikipedia says this feature is caused by erosion from glacial meltwater, not carving by ice.
And their article says this:
"the hollow may become a large bowl shape in the side of the mountain, with the headwall being weathered by constant freezing and thawing, and as well as being eroded by plucking."
http://en.wikipedia.org/wiki/Cirque
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Also from Wiki:
"Glacial plucking exploits pre-existing fractures in the bedrock. This plays a key role in opening and creating new fractures but has only provided small segments of loose material. This is then followed by the entrainment of the loosened rock by the ice. During the process of entrainment, loose rock material is frozen onto the base of the glacier and incorporated into the glacial ice. It is significant when the bedrock is highly jointed, as this allows meltwater to penetrate. Plucking is also known as quarrying.
As the valley glacier moves down the valley there is friction with the rock floor. This causes the basal ice of the glacier to melt (which helps lubricate the movement of the glacier)and infiltrate joints in the bedrock where it then freezes. As the glacier moves on, the rock now bonded to the glacier, is plucked from the floor into the base of the glacier and carried with it."
Wikipedia has been known to be wrong but hey, I’d never heard of this Creux-du-Van before this thread was posted.
Wonder if there are the same kind of formations in our own glacier parks.