Forest Service National Avalanche Center Layers in a thinly sliced isolated column of snow are illuminated by the sun. The snowpack accumulates layer by layer throughout the winter with each new precipitation, temperature and wind event. There are both strong and weak layers within a snowpack. Strong layers tend to be denser layers comprised of small round snow grains that are packed closely together and are well bonded to each other or cohesive.
Weak layers tend to be less dense layers that are comprised of poorly bonded or cohesionless grains.
Because weak layers prevent strong layers from bonding with one another, it is important for the backcountry traveler to know the relationship of these layers. Sometimes it is helpful to think of the strong layer as a brick and the weak layer as potato chips. When the potato chips are on top of the brick there is no problem, but reverse the order and put the brick on top of the potato chips and you have a problem. The weak layer, potato chips, may not be able to support the strong layer, brick, and if the slope is steep enough an avalanche could occur. More importantly, sometimes the potato chips are just barely holding up the brick and all it takes is a snowmobiler adding their weight to an already stressed snowpack to trigger an avalanche.