You’ll have this very popular area all to yourself in the winter. Mt. Ritter from San Joaquin Ridge.
Winter is a wonderful time to visit the backcountry! In the winter you’ll have the most crowded locations to yourself. Overused areas are refreshed with a tinsel of snow and places you’ve visited a dozen times are exciting and new! However the snow of winter adds challenges and requires additional skills. You’ve got to know how to stay warm and dry both while moving quickly on sunny and stormy days….and once your activity level drops in camp. Navigation must be performed quickly in stormy conditions with limited visibility...when the trails and even trail signs are buried. The snow that adds so much freshness to the backcountry also adds the deadly danger of avalanches. Before you head into your winter wonderland you’ve got to know the season’s snowpack, the weather you’ll be facing and how to assess the risk of avalanches in the terrain you plan to cover and make the best route decisions to minimize those risks.
This article presumes that the reader has a basic knowledge of how snow behaves. It assumes that you will travel in a group and that each group member will carry an avalanche probe, beacon, and metal-bladed shovel and can deploy them within 10-15 seconds. Avalanche probes, beacons, and shovels can save lives but they are no guarantee of safety. While it is critical to know how to use them successfully (and their use is beyond the scope of this article), you cannot count on your beacon and probe to save you! You’ve got to know where, when and how to travel and rigidly follow the rules you’ve set up. You must approach snow with the mindset that coming back alive is more important than completing a route or skiing a fun but dangerous line. That mindset is crucial.
Let’s dispel a few myths. First, most avalanches are not huge avalanches that rip out trees and send house-sized boulders cascading into valleys. They are small and release after storms and changes in weather. Second, most avalanches do not kill by burying their victims. They are more likely to kill by sending an unsuspecting skier over a cliff or by smashing them into rocks or trees. Third, most avalanches are not random events from a side ridge. They are usually triggered by their victim. Finally, having a probe and beacon does not guarantee your safety. They may save your life and certainly make it easier to find your body but alone their use means a life threatening event has already occurred. Let’s keep that from happening!
A small avalanche below a steep glacial slab. Going over the cliff above would not have been healthy.
Knowledge is Light! (Scientiae perfusorius est)
As with so much in lightweight backpacking it’s not what you carry but what you know that keeps you safe. Understanding that a beacon and probe won’t protect you means that you have to carry a cautious attitude and a working knowledge of snow safety into the backcountry when you visit. Fortunately these don’t add anything to your baseweight!
Sastrugi give evidence to the transformative power of wind.
Snowpack Evaluation and Transformations
Evaluating the snowpack begins with the first snows of the season. This is true even if your trip doesn’t happen until March. I follow the base layers of snow, the temperatures at which they fell and subsequently settled, and any rain especially early in the snow season. Snow falls as a series of layers. Once it falls it is changed by a combination of wind, sun, rain, a high temperature differential between the ground and the air, and warm temperatures. Each of these factors can increase or decrease the avalanche risk.
Thin snowpacks and high differential temperatures between the ground (32 F) and air promote the formation of dreaded “depth hoar.” Depth hoar is a type of reformatted snow that develops from the constant melting/refreezing cycles driven by large temperature gradients. Depth hoar has few sharp edges and behaves more like crushed ice. It has little cohesiveness. This is a loose crystal type of snow that is very unstable. Put a load of heavy snow on top and it is prone to slide. Early depth hoar development can leave unstable layers in the snowpack that can last the entire season. And you’ve got to know about them. Rain on top of snow often forms an icy layer that provides another unstable surface prime for avalanches. Really warm days before a cold storm can also lead to icy layers. Icy layers don’t hold snow well. New snow will often release from the top of an icy layer.
Sudden and new increases in the ambient temperature (often increased by the “reflector oven” effect of bowls) result in less bonding force within the snowpack, and this is a major time of increased avalanche risk. If you are traveling on the first unseasonably warm day of the season or any day above recent average temperatures, watch out! In the Sierra we often travel before sunrise and only until 12-1pm on warm days to avoid avalanches. (But if we’re making miles we may start again at dusk and travel well into dark.)
Fresh snow on top of this icy surface would not hold very well. It is a prime avalanche location.
When snow falls it usually does not stay where it fell. Storms are almost always associated with wind and inches of snow can be redistributed to the leeward side of ridges and gullies. These “wind loaded” slopes get way more snow deposition that the windward side during a storm. The snow is often packed together into “slabs” that behave as a unit and are much more prone to avalanches until that snow has settled. This is especially true if there is an unstable layer of powder, hoar, or ice beneath it. One of the important wintry backcountry skills is determining where the winds have deposited the last storm’s snow. Just by looking at the scene you need to be able to see how the snow has been influenced by the weather and where possible avalanche sites have formed. Also the wind direction needs to be determined from the current wind direction as well as the snow ridges behind rocks and trees; snow will build up behind trees and rocks on the side away from the wind. Cornices are also a good indicator of where new snow may be deposited and where possible avalanche areas may be found since they form on the leeward side of the ridge. In short, the leeward side of ridges and ribs are much more unstable for several days after a storm. Don’t travel there!
The illustration below (from Allen & Mike's Avalanche Book by Allen O'Bannon and Mike Clelland) and the video shows how snow loads on slopes.