An oft asked question in glacier-travel training is, "What's a moulin". A french word, pronounced "moo - lan", its a name for a vertical tube in a glacier, carved by water and acting as a drainage tunnel.
From an artistic perspective they are mesmerising, from a climber's perspective, they can be terrifying, deadly - and if you fall in one un-roped - it's a one-way ride with no exit at the bottom. Often hidden by snow, they are another reason why roped travel and practice are essential considerations in mountain travel.
Now scientists are studying moulins as a way to understand glacial movement, ice change, rising sea levels and climate change.
Click here to read a fascinating article on moulins.