Maybe it's encediary gas?
Could also be that they are scraching the ground so the walkers can't walk on it anymore.
Edited by YariSamuraiLast Jedi screen grabs of ... uh ... the "Bloody Blade Runner!"
57 minutes ago, Force Majeure said:Is that the correct way to spell Crait? Just want to clarify, because if it's "Krayt," then one could speculate that we may see a Krayt Dragon in this battle. Dragging those poles in the sand might disturb a sleeping one that comes out to battle AT-As.
Yes, I believe the spelling is correct, but man, that would be epic.
The spelling comes from a Bleeding Cool article, which is the only place I've looked at for reference so far.
BC has notoriously bad spell checkers.
Edit: oh hey, look, it's my 1000th post! 
I get the feeling it's some kind of cloak effect, to shield troopers/anti-vehicle specialists from the AT-AT fire, much like smoke grenades, but a bigger area covered plus it looks cool.
On 2017-04-15 at 0:41 PM, kitandthevoices said:also i don't think these are being flown by the resistance. I think this is going to be somewhere towards the start of the movie showing the growing strength of the first order as they conquer outer rim planets which have to rely on their own local militias.
This would be very fitting with the new Republic. The New Republic has a very small military, with planets defending themselves, with Aid from the Republic. With the majority of the fleet wiped out, these local forces have to fend for themselves
My guess is that the red dust is mineral laden, and hides the speeders from sensors due to ground clutter type effect. Which makes them harder hit as they close, and will give them the edge when the FO walkers get enveloped by the dust.
http://nerdist.com/the-last-jedi-director-rian-johnson-reveals-new-star-wars-planet/