Snowplows and Snowhogs: Getting to know the Avalanche Effect

 Digging through snowplow-created berms during this weekend's storm: I sent Son #3 to scale the ridge line with a shovel. He on the street, me on the driveway, we attacked it from both sides. First we made a hole and shook hands like sandhogs working on a tunnel from both ends, then went at it with a will until the hole was a valley and finally a gap big enough to drive a car through. Wished for a tunnel-boring machine.


Those living south of the snowplow line may be surprised to hear that snow gently falling on the ground is not the same as snow that has been pummeled by a snowplow blade or, even more, transformed by a slab avalanche.


This phenomenon is rarely depicted in action movies. I suppose it's because the screenwriters haven't been close to an avalanche, nor read much about them.


Slab avalanches leave anyone alive trapped in icy debris that is most impressively dense and hard. This set-up happens instantly, as the friction-heated snow refreezes. Here's an illustration: a hiker whose lower leg is covered by the fringe runout of a slab avalanche will not be able to get her foot loose without literally chopping the ice away. The consistency is something like cured, low-grade Plaster of Paris; not quite as tough as concrete, but not something she can gouge with her hands. Without a metal shovel or better yet an ice axe close to hand, she'll be lucky to get loose, boots or not. Here's an explanation from the Utah Avalanche Center, including a narrative of what it feels like to be inside one and survive.


Which leads me to a book I highly recommend for outdoorspeople: Ian Stark's Last Breath: The Limits of Adventure. It's grim but excellent reading, and goes far to strip away dangerous and foolish notions about the course of medical emergencies in the wilderness.


Each of the eleven chapters is a fictional narrative, with all events grounded in medical fact and relevant physics (as in, the physics of snow and debris in an avalanche). Some of the fictional characters survive; some don't, so there's an element of suspense in each tale. I thought I knew about dehydration until I read Stark's last chapter, "In a Land Beyond the Shade."


Rather than leave readers with bad feelings about snow, here's a picture from the storm: a pretty little cornice that formed under the eaves of our house, changing by the hour as a brisk wind carved here, and added there.