Saggy Baggy Snow
On a recent winter drive I stopped to shoot some photos of the snow covered rocks alongside the road.
My initial interest was in showing the layers that were visible in the edges of clear spots where the rock face projected through the near vertical pack. As you can see in the picture on the right these layers are laying down horizontally.
After inspecting a few of these on close-up I noticed something else was happening as well. And learned something about snow pack I didn't know before in the process.
What I saw was another layering effect.
As you can see from this picture the exposed face appears to sag away in a vertical face slice with a lip forming at the left side. On the right side you can see a formation much further along in its evolution. It has become a pocket.
I made a larger stitched image that you can browse around in and see more of these formations. The rock face is on the east side of Highway 3 near the intersection of Hwy 3B.
If the controls are not visible: with the mouse over the picture use the Shift and Ctrl keys to zoom in or out. Click and drag with you mouse to move around.
As you can see in the larger image the top side of a hole typically becomes an overhanging shelf. Much of the snow cavities surrounding the exposed rock appears to have formed this way.
The snow appears to get heavy and soft and then a slit forms at a point where the snow pack shears due to the forces at play. Once that slit forms it enlarges and deepens. With day/night cycles and subsequent snow falls the weight goes up and down and new layers get added above the exposed snow.