Tried to resist answering but like a moth to the flame.....
Carbon fibre is very fragile. I belive that going with the weave it has a strength but againstthe weave it is as fragile as glass(ish) - it might be the other way around but the principle stands. The strength of a carbon fibre item is wholly related to how many layers of "cloth" are used and the complexity of overlaps of the "weave". Cheap carbon fibre will have few overlapping layers, expensive will have more and with more attention to the interplay of the weave overlap in relation to the expected stresses.
Expected stresses is a key point. when working with windsurfers, who had carbon fibre masts, the masts would take tremendous stress from the wind/sail i.e. at right angles (roughly) to the mast but if they fell off the roof of the van and landed on the tip - they would crack down the lentgh of the mast. Stress from the end of the tube was not designed into the fibre structure, hence weakness.
Carbon fibre tripods can be very strong but I would not hit it with a rock/hammer etc without being prepared to replace the component afterwards. Nor would I buy an inexpensive carbon fibre tripod for use in extreme situations.
As has rightly been said earlier, irrespective of the material, anything that gets wet then exposed to cold temperatures will freeze. Water expands on freezing so expect jammed bolts, joints tubes etc.
Gitzo do make a tripod designed to be used in the sea, not sure about freezing sea, and Benbo tripods by Paterson have the lower leg sealed against water ingress - might be a good start point to research further, but unless you can afford to use tripods as one-use disposables I would seriously not suggest hitting them with anything let alone a rock.