Our beautiful Fraser Valley mountains are a magnet for those looking for fun and adventure outdoors. Planning, preparation and informed decision making are key to maximizing fun and minimizing risk. Avalanche danger in BC is well known and to ensure you and your group get home safely, there are skills to learn and danger signs to avoid.
Ten Common Avalanche Myths:
1. “The slope I’m on is not steep enough to enable snow to slide.”
Most slab avalanches (about 95 percent) release on slopes between 30 and 45 degrees. However, under certain conditions, avalanches can be triggered on slopes shallower than 30 degrees. Perhaps where a very weak snow layer such as surface hoar, or where new snow is struggling to stick to a smooth sun crust. It’s not uncommon to trigger an avalanche from nearly flat terrain at the bottom of a steep slope, called a compression zone. It’s like pulling the bottom can from a nicely stacked pile of soup cans at the grocery store…”crash!”
2. “It’s got tracks. It must be safe.”
With tracks already on a slope, you might naturally assume it is safe, but the opposite may be true. The initial tracks could have begun a failure process that a second transit may complete, allowing the slope to fracture and avalanche. Secondly, it’s folly to depend on previous hikers as your guide. Assess slope safety yourself and avoid the temptation to simply follow in someone else’s footsteps.
3. “There isn’t enough snow to avalanche.”
Avalanches are not uncommon in the fall before the deeper snows have accumulated. Hunters, climbers and enthusiastic, early-season snow seekers are the likely victims. Snow on a steep hillside does not need to be deep to avalanche, regardless of the time of year. It just needs to be deep enough to form a slab that is not anchored by rocks or vegetation. Also, last winter’s snowfields make a very smooth bed surface on which early-season slabs could slide.
4. “It’s been a low-snow year, so there’s little avalanche danger.”
Actually, the opposite may be true. When little snow has fallen during the winter, shallow snow cover becomes very weak as internal water vapour dissipates and it develops into a faceted snow structure. Faceting changes rounded crystals into faceted ones (more, but smaller surfaces)—thus changing strong snow into weak snow. Faceted snow can easily crumble under the weight of a person or heavy, fresh snow, because the grains have poor bonds with their neighbours.
5. “The avalanche slid on a layer of ball bearings.”
Some people use this description to describe how an avalanche ran on a buried weak layer. Technically, this is not correct because it implies that round snow grains were involved in the snow failure. In fact the weak layer was likely composed of faceted, sharply-angled snow particles, not round like ball bearings. The more facets a snow crystal has, the less able it is to adhere to its neighbour particles and therefore more likely to slip past one another causing an avalanche.
6. “The slope faces south, so it’s safe.”
It is true that snow on sunny slopes tends to be more stable due to settlement and bonding. However, sunny slopes have their own unique avalanche problems. For example, if there is excessive sun exposure, surface melting will occur and any water that runs down into the snowpack will destroy the bonds holding snow together. Upon refreezing, a smooth ice crust forms on the surface and subsequent new snowfall has trouble sticking to it. In another process called radiation recrystallization, a thin layer of faceted snow is formed just below the surface. When buried by more new snow, this fragile layer can contribute to avalanche formation.
7. “It hasn’t snowed for a long time. There won’t be an avalanche today.”
Even without a recent snowfall, wind can move existing snow, causing drifts on lee sides of steep ridges and gullies. This adds load and stress. A sustained, heavy wind can cause blowing snow that creates dangerous and unpredictable hard slabs. Even absent wind, old snow often becomes weaker with time, as kinetic metamorphism forms faceted snow and unstable layers.
8. “A heavy snow winter causes more avalanches.”
Avalanche danger is often not about the amount of snow, but the speed of accumulation. Short periods of heavy snowfall will increase avalanche danger dramatically. If the same amount of snow were to fall evenly over a few weeks, a stronger snowpack would form. This is due to a temperature pattern developing in the snowpack that forms rounded, well-bonded snow grains and preventing the formation of weak, faceted snow and depth hoar (frost).
9. “The last snow was two days ago, so the new snow has stabilized by now.”
Not so fast! The effects of temperature and loading must be considered. If temperatures following the storm remain quite cold (below -10C), new snow settles and stabilizes slowly. It could then take days or weeks for the new snow to become stable. Warmer temperatures (above -10C) speed up the stabilizing process. Then there is the loading effects of the last snowfall. A recent snowfall may have put enough additional stress on the old snow that it is now close to its failure point. Before, it may have taken a large trigger, such as a snowmobile, to collapse a deep weak layer. Now, the weight of one skier or snowboarder might be enough of a trigger.
10. “Avalanches don’t run in trees.”
Although avalanches do not initiate in thick forest, an avalanche can run down through a forest if it starts in a large open area above the forest. Being in the trees may not be safe if an avalanche starts in a sparsely covered area above you.