Ever notice that the berm across the end of your driveway, or the one formed when you shovel the sidewalk, is harder than the undisturbed snow? That’s because when snow is disturbed crystals are broken, and the broken surfaces positively grab onto other ice surfaces. Two examples of this are common in nature, and I’ve used both in my fiction writing.
The first is called a wind slab or wind crust. When a turbulent wind picks up snow crystals and redeposits them, a good deal of crystal breakage takes place. When the broken crystals settle down they weld themselves to other crystals and the result can be a hard crust—even though the temperature is below freezing. Roi has to cope with this in Tourist Trap:
The trees had broken the force of the wind up to now, but once he entered the open swath the wind almost knocked him off his feet. The snow was crusted here, not quite enough to hold his weight, but enough that his thighs were bruised repeatedly by the chunks of wind-slabbed snow he was dragging Timi through. He paused twice to increase the circulation to his feet. Were they cold, hurting like hell, or just numb? he wondered absently, and then realized that Timi’s shields had dropped to the point that he was feeling Timi’s body as well as his own. The wind cut through the frozen scarf and the cold glued his eyelashes shut, and with a start of horror he realized that he had drifted away from the line back to the shelter. He could teleport himself back, maybe—but he wasn’t sure he had the energy left to do even that, and there was no way he could take Timi with him.
He struggled on: lift a leg and break the crust with his knee, then drag the leg through the slightly softer snow underneath until he could balance on that leg to break out the next step with the other leg. Timi staggered behind him, almost falling several times, and his mind ached from the effort of keeping the other boy upright. Snow had sifted into his clothing, somehow, and he knew he was cold but no longer felt it. With an abruptness that caught him by surprise, the wind died down, and he went to his knees as he tried to break through a crust that was no longer there. Back in the trees, he finally realized, and reached out for the faint impression of the shelter.
The second is probably less familiar to most, and I hope it remains so, but here in Alaska it is constantly being drummed into us. This is what happens in an avalanche. The churning snow sets up like concrete as soon as it comes to a halt. Well, not quite like concrete — it can be dug through with shovels – but far too hard to shift by moving your body. Marna is caught in an avalanche in Homecoming:
Even as she crouched and aimed herself for a belt of trees that might provide some protection, the leading edge of the avalanche overran her, tumbling her helplessly down the slope. The churning snow caught and twisted one forceweb until she thought her leg would break, but the torsion activated the safety cutoffs and the forcewebs went abruptly inert. She clawed her way upward through the fast-moving snow, and tried to remember what lay downhill. Only her perceptive sense kept her from total disorientation.
The buffeting and spinning as she was carried along reminded her of the time she had been caught in the breaking wave—but then Win had been there to rescue her. Win. She had repudiated whatever was left of Win, but as the slowing mass suddenly set rigidly about her body, she wondered at her own insanity in wanting to be alone. She struggled to move, but felt only the slight snapping of a switch, followed by the growing cold of the snow that held her prisoner. Her struggles must have turned off the thermal suit, she realized with a growing sense of despair. Exhausted and chilled, she could not even visualize a place of safety. Win, she sobbed mentally. Forgive me, my love.
This is a situation where time is absolutely essential, and buried but living victims are likely to die of suffocation or cold – often in less time than it takes to get help. Dogs are better than people at finding victims, but if search and rescue dogs have to be flown in, it is often too late to find anything but a body.