Sparkling deep powder near the red-rated Mephisto run tempts, but off-piste in Flaine is dangerous because of the "lapiaz", deep longitudinal crevasses in the limestone. A chemical action of water and salt deposits erodes large holes in this rock, rain water then runs into these holes further eroding the surface. From the point of view of the skier or snow shoer going off-piste the dangers are the same as crossing glaciated terrain. Snow bridges of varying strength form across these fissures and particular care should be taken early in the season or in seasons with poor snow fall.