I have discovered that using a tripod in deep snow should be done with care. I broke my tripod in Hokkaido as a result.
I've learned that rather than spreading the legs as wide as they can go before lowering the tripod into the snow, I should leave some room for the legs to spread further apart once the tripod begins to sink downwards. This is because the legs slide down at an angle - and therefore move further apart as they go deeper into the snow. So they need some room to spread out.
If the legs are already spread as wide as they can go before lowering the tripod into the snow, the snow will try to spread them even further apart and this will put a lot of stress on the joint at the top of the leg (in my case - it fractured as you can see in the photo below):
My guide had some duct tape, which I forgot to bring this time with me (I normally travel with it - worth bringing - you can use it for many things) and it did the job well for the remainder of my time in Hokkaido.
I wouldn't blame Gitzo for this: there's only so much stress a tripod can take, and I abused it by forcing the legs to try to spread out further than they could go.
My tripod is now back to 100% functionality. Thanks to the modularity of the Gitzo system, I was able to buy a replacement column from www.gitzospares.com (around £100), and replaced it in a matter of minutes. Much better than having to go out there and buy a new tripod at over £650. So I'm very pleased.
I might invest in a complete leg as a spare, for the checked-in luggage ;-) I seem to need spares of everything. Perhaps the next replacement part I'll be needing is a replacement-me ! :-)