Most people think that the Vallee Blanche is the big long glacier run from Aiguille du Midi all the way down the Mer de Glace. The fact is, the true (in French 'vraie') Vallee Blanche is just a shorter section of descent (800m vertical) of quite heavily crevassed terrain between Gross Rognan and Petit Rognan. They are two pretty noticeable rock outcrops to the west of the Midi station. The vraie Vallee Blanche is seldom in good condition, which is a shame as it is some of the better terrain along this disgustingly over crowded descent from the Midi to Chamonix. Most people, 100's per day, if not more, descend around the sides of the Vallee Blanche, that is to the left or the right of the two Rognan features, but seldom in between. Regardless which of the 'Vallee Blanche' routes you take, you will end up on the incredibly boring Mer de Glace. Great scenery, but crowded and flat. Just to get onto it usually requires a nasty heel side traverse for natural footers. This traverse takes you below some seracs right about the time your legs are bursting and screaming for a break. But it not a good place to stop.
I have been down this general route several times and the Vallee Blanche entry is the best. Although, after fresh snow and in the incredibly rare instance that the crowds are low, the rout to the skiers right of Gross Rognan is wide open sustained 30 degrees for almost 2 kilometers of horizontal travel. It is crevassed, so you have to stay alert, but it is none the less a fantastic slope. I have never had it those conditions, however I did ride down that way in May 2006 when the winter tourist crowds had vanished. There was 2000m of pretty good spring corn all to ourselves. There wasn't another person in the valley, which by comparison to the obscene crowds, was quite surreal.
The enormous Helbronner descent also ends up on the tedious Mer de Glace except you enter from the east, rather than the west (from the Midi). There are loads of ski mountaineering touring routes that start on, end on or require a traverse of the Mer de Glace or Valley Blanch area. If you are busy in Chamonix, you are going to get plenty of time in this tourist arena.
To get off the Mer de Glace you can catch a little train down the hill to Chamonix. This departs from well down the glacier and requires a short gondola ride up to the station. It is for the tourists and gets insanely busy on a sunny weekend. The alternative is to find your way up the side of the glacier valley (on the skiers left) just a little further down from the 'train station'. This puts you on a cat track consisting of some fun but tricky switch-backs below the tree line. If the snow is deep then you can fly around the corners, but if you stuff up you often fly over the lip of the berm, off the track and into the trees. I have seen some great crashes down that track.
All in all, what is sold to tourists as the 'Vallee Blanche' is not worth your effort more than once. The first time is a great way to get very close to some amazing scenery. But the riding is not a high point. However you will meet this area often on other tours and also if you are practicing your crevasse rescue systems in the relatively safe trampled lower crevasses.
Looking down the left hand side of Gros Rognon into the vraie Vallee Blanche (the crevassed area in the very near ground). A crevassed area of the Glacier du Tacul runs right to left and down towards the Mer de Glace. The open area in the upper right is the run down the Geant Glacier from Ponte Helbroner.
Myself on my knees and a group of riding buddies in Feb 2005 breaking the rules and taking our boards off in a crevassed area of the Mer de Glace. The guy on the left smashed his hip up in Austria riding powder during the early snowfalls of Dec 2005. As of Aril 06 it is still uncertain if he will ride again. I hope he can.
Looking down the left hand side of Petit Rognan and onto the heavily crevassed area 'up steam' from the flat long Mer de Glace. This is one of the very few 'steep' lines. You can see a loitering tourist crowd at the bottom. We were the same as them that day. Just another bunch of people in the crowds.
Looking back up the crevassed area that features in most of these pictures. I am standing on the Mer de Glace. The route through the crevasses is via a nasty traverse on the skiers right and then down the rear side of the large rocky spur in the foreground. Once again, see the crowds.