A storm on the descent from the Col d'Iseran dropped hail and ice and sent ice melt from the glacier washing a thick river of mud across the race route.
Crews tried to clear parts of the road with plows but the race officials took the decision to stop the stage as Egan Bernal (Team Ineos) was on the attack.
The riders, racing on dry roads on the other side of the pass, were unaware of the dangers ahead and were confused as to the decision. At the time of the stoppage, Bernal was up the road after attacking on the Col de l'Iseran and had about one minute over a chasing group with Geraint Thomas, Stevn Kruisjwijk, Emanuel Buchmann, Vincenzo Nibali, Rigoberto Uran and Mikel Landa.
The race leader Julian Alaphilippe (Deceuninck-Quickstep) was further back, approximately 2:09 behind Bernal.
Because of the stoppage, the officials did not award any stage winner, most combative rider or time bonus for the stage.
Race officials took the times for the general classification times at the top of the Iseran, putting Bernal into the maillot jaune over Alaphilippe with Geraint Thomas (Ineos) in third.