Today’s stage was cut short by a storm in the Tarentaise Valley. The sudden thunderstorm brought hail and snow and a whole lot of water onto the roads and hillsides of the final descent towards the Lac du Chevril. The sudden addition of all that water created some landslides which completely blocked the road.
Landslides have also occurred on the route of the stage tomorrow, so the organizers have shortened that stage to just the climb of the Val Thorens.
When a lot of water falls on the slope in a short period of time (such as during a thunderstorm), the water starts accumulating in the pore spaces of the soil, exerting a force on the particles of soil and pushing them apart. Once that force exceeds the strength of the soil, it breaks the soil apart. Steep slopes mean gravity pulls hard on this loose soil and it runs down the mountainsides. Mass wasting like we saw today is thus fairly common in alpine regions, and there is growing concern that increased precipitation combined with warming soils may make them [even more common](https://www.nature.com/articles/s41561-018-0177-6), which does not bode well for future editions of the Tour de France.