Tony Tsuboi
In the wintertime, we often think of slab avalanches as our main problem to contend with. However, before you know it, springtime will be upon us. Our days are already growing longer, the angle of the sun is becoming more direct, and the average temperatures in the mountains are rising.
This blog is intended to raise awareness of the snow hazards most likely to affect us as we crawl out of winter’s darkness and enter our high-activity seasons in spring and summer.
What are spring snow hazards?
Tree Bombs
Winterlike conditions can extend well into March and April. Before heading out on a trip, ask yourself: was there a recent storm that deposited new snow? Heavy snowfall can leave snow-covered tree boughs that linger above our hiking trails. The trees are pretty that way, but when temperatures rise and the sun comes out, dense snow or ice piled on tree boughs may fall in the form of hundred-pound “tree bombs.” During your trip, look and listen for drips of melting snow. If there are frozen tree boughs above and warm temperatures, tree bombs are a hazard to manage.
Snow piled on a tree bough, which may eventually fall as a "tree bomb."
Wet Loose Avalanche
These same conditions – sunny, warm temperatures after a snowfall – precipitate Wet Loose Avalanches. While this avalanche problem type also occurs in the wintertime, Wet Loose Avalanches become the predominant avalanche problem to manage in the heart of our high-activity seasons. When it’s warm and the sun is out, think through your route. Does it pass through avalanche terrain? Remember, avalanche terrain includes an avalanche’s runout, which could cross a hiking trail.
Wet Loose Avalanches are sometimes considered benign, but that isn’t always the case. If they run long, they can entrain a large volume of snow, more than enough to knock you off your feet. Certain terrain features, such as gullies, can amplify the depth that accumulates. A river of snow can drag you over a cliff or into the strainer of tangled trees below. All of these factors have potential for harm.
How can you avoid Wet Loose Avalanche risk? Terrain choice is one option. Wet Loose Avalanches initiate on steeper terrain, but they can run long and well into lower angle terrain. Try to cross runouts or terrain traps earlier in the day to mitigate exposure, or find another path that avoids Wet Loose Avalanche terrain altogether.
The southeast and southwest parts of a mountain get more sun which increases the risk of avalanche. Timing when to cross these parts of the mountain adds a dimension to route planning. If you need to cross potential avalanche terrain, try to manage your schedule to avoid peak sun exposure. Avoiding peak sun exposure is the primary reason why climbers will get an “alpine” start in the wee hours when climbing volcanoes.
An avalanche example on Colchuck
The following video is from Colchuck Couloir around late May. Extended warm weather preceded this event. By the looks of it, the time appears to be late morning to mid-day, and the sun is in full effect. What might you do differently? How would you enact the strategies above to manage Wet Loose Avalanche hazards? Other Avalanche Problem Types related to warm weather and sun include Wet Slab Avalanches, Glide Avalanches, and Cornice, all of which involve similar risk mitigation.
