The Dark Layer of Tuckerman Ravine
By Jason M. Denoncourt, Chemical Engineering, 2023
Every spring, thousands trek up the Tuckerman Ravine Trail on Mount Washington in New Hampshire. Trudging through mud with skis and boots precariously strapped to their packs, their destination is Tuckerman Ravine, a glacially carved bowl regarded for some as the most accessible and steep backcountry skiing in the east.
For the majority of these skiers, a spring day on “Tucks” means a good time with friends and family — skiing, building snowmen, or just hanging out by the “lunch rocks” at the base of the bowl. However, for an unlucky few, serious injuries caused by accidents and avalanches are a reality.
Though avalanches are far less prevalent in the springtime, extreme caution and attention to warnings posted by the US Forest Service should be taken no matter the season. In fact, most injuries are commonly a result of a lack of backcountry skiing experience and avalanche education.
Veteran skiers can identify vulnerable patches of snow to avoid when hiking and skiing on Mt. Washington or any other avalanche-prone terrain. Knowing how avalanches form, how they are released, and the different types of avalanches provide a foundation for proper mountaineering safety.
Knowing how avalanches form, how they are released, and the different types of avalanches provide a foundation for proper mountaineering safety.
All snow exists in layers, with varying levels of cohesiveness and rigidity. The primary cause of an avalanche is weak snowpack layers. Typically formed of more granular snow, weak layers fracture under stress — whether a result of new snowfall or an unsuspecting skier — and trigger avalanches.
Aspect, or the direction a slope faces, has a profound impact on snowpack. In the northern hemisphere, north-facing slopes receive very little solar heat. Likewise, east-facing slopes receive sunlight primarily in the colder mornings. This cold snowpack is the most attractive to skiers, as this type of snow is often fluffier. However, cold snowpack is also more likely to form weak layers. The popularity among skiers and the increased likelihood for weak layers accounts for why the bulk of avalanches occur on north or east-facing slopes.
Anchors also play a crucial role in the formation and release of snow slabs, which are cohesive plates of snow. An anchor is any tree, bush, or rock that protrudes through a slab and holds it in place. The thicker the distribution of anchors and the greater the anchor penetration into the snowpack, the less the risk of avalanches. Likewise, low branching trees, like spruce and fir trees, are far better anchors than trees with few low branches, like aspens and lodgepole pines.
The popularity among skiers and the increased likelihood for weak layers accounts for why the bulk of avalanches occur on north or east-facing slopes.
There are two major types of avalanches: slab and loose snow. Slab avalanches are often referred to as the “White Death” or the “Snowy Torrent.” As these nicknames suggest, slab avalanches are the most dangerous and account for nearly all avalanche deaths in North America. In a slab avalanche, a cohesive plate of snow slides down the slope. These plates are primarily formed between and released at anchors. As a result, it’s very common for a skier to be in the middle of a slab as it gives out and the avalanche forms. These quickly become deadly, as the plate shatters into smaller chunks and accelerates to speeds of 80 miles per hour within 6 seconds.
While it’s common for slab avalanches to release above a skier, which often proves deadly, loose snow avalanches usually release at a singular point below or at the feet of a skier. For this reason, these avalanches are far less dangerous and are frequently referred to as “point releases” and “sluff.”
As a skier, getting caught in an avalanche is often just a matter of being in the wrong place at the wrong time. These dangers are inherent to the sport of backcountry skiing. However, the risks of serious injury and death can be minimized with proper preparation, education, and gear. Technologies like the Recco System — comprised of reflectors installed in clothing and a transceiver — can save valuable minutes in finding people buried in avalanches; statistics show that 93 percent of victims are recovered alive if found within 15 minutes while only 20 percent survive after 45 minutes. In regulated areas, examinations of the snowpack layers are used to determine an avalanche rating, ranging from low to extreme. In many west coast resorts, ski patrol uses explosives to trigger avalanches in a controlled environment. On Tuckerman Ravine, avalanche tests are performed daily by the US Forest Service and a volunteer ski patrol is present in the case of any incidents, keeping the skiers, snowmen–builders, and lunch crew safe and smiling.
