Opposites Collide
Deconstructing the destructive forces of fire and avalanche.
By DEREK ELLIS

As I push up the ridge through knee-deep snow, a rising swirl of spindrift erupts from the trees across the canyon. Suddenly the tired crystals below my skis collapse, and the sickeningly familiar whoompff emanates from the ridge. My heart reminds me that entropy lurks in these hills today. The pulse of adrenaline brings to mind the heat of August and another power that bides its time in the mountains: fire. The whoompffing of snow under skis turns to the crackle of tinder-dry sticks under boot. Smoke, not spindrift rises from the trees across the canyon.

Fire and avalanche. Skinning through a beautiful stand of well-spaced Doug fir, I think about their similarities. The paradigm for both fire and avalanche education emphasizes a triangle of elemental relatives. On the hot side, topography, weather, and fuels combine to create conditions for sustained energy release. On the cold side, topography, weather, and snowpack work in very similar ways to form a different energy release. I pause at a favorite chute through the steep trees. Forty-degree powder beckons in sumptuous pillows, but the thought of avalanche debris collecting in the curving gully urges me elsewhere.

Avalanches and wildfires favor very similar terrain. Several fire fatalities, including Storm King (1995), have occurred on steep slopes, often with gullies. The rising heat dries out and ignites the fuels positioned above it, and draws in air from below, fanning the flames. This combination results in rapid rates of fire spread. Just as increasing slope angles add tension to the weak layers of a snowpack, increasing angles of fuel beds cause energy-release potential to rise. Narrow gullies are avalanche terrain traps. Steep drainages funnel wind and heat resulting in infernos of turbulent flame, potentially fatal places for firefighters.

Ducking around a large cornice, I cross onto a southwesterly slope. The luxurious powder turns sour and I blast through large chunks of zipper crust on my way back to the soft northerly snow. Aspect, a terrain feature, plays a large role in staying safe in both avi and fire terrain. The increased solar radiation on southerly aspects has a great effect on both fuels and snowpack; both are often thinner and more responsive, flashier. The grasses and shrubs that dominate southerly slopes are more reactive to daily fluctuations of temperature and humidity than their northerly counterparts. Similarly, the sun-affected southerly snow slopes can quickly become dangerous on a warm spring day due to rapid heating of the upper layers of snow. The more protected northerly aspects hold moisture and are often densely vegetated. These slopes are resistant to fire early in the season, however they can sustain intense burn when conditions are right. Northerly slopes are also more resistant to change in the winter, although the shelter that promises powder turns may also cultivate and protect weak, faceted snow and instability.

Continuing along the ridge to my powder stash, I scan the mountains in the area. A white flag waves above the highest peak to the south. High winds are hammering the upper slopes and the spindrift of snow loading on the northerly leeward slopes makes me glad I chose not to climb higher. Just as a trained fireman continually monitors for conditions that could result in entrapment, every powder junkie keeps his or her eyes on the weather. Rapidly rising temperatures and high winds sound alarm bells to fire and avalanche professionals alike.

Popping out of a treed ridge, a bowl of tasty powder unfurls below. Recent snow and wind, in combination with the steep, avalanche-prone slope, make me wonder what's under my skis. I plunge my pole beneath the surface to get a feel for how the new snow is stacked on the old, much the same way that I dig into the forest floor to examine the dry summer fuels.

The third leg of the fire and avalanche triangle is the substrate, either the snowpack or the fuel bed. Fire and avalanche create rapid physical changes to the outermost cover of the Earth. The accumulation of dead organic material and flammable live material on the ground creates a structured layering of fuels. The physical properties of the fuel alter how responsive it is to fire. Fine, dead grass creates a layer of very flammable fuels that dries quickly and is highly responsive to change. Easy to start, easy to put out. On the other end of the spectrum, heavier fuels take days and even weeks to dry to the point of being flammable, but then can sustain fire for a relatively long time.

In a similar manner, the various layers in the snowpack react to loads in different ways. Cold weather creates delicate crystals with many air spaces and complex structures. These crystals are very reactive and, buried, can trigger larger events, like the flammable grass will stimulate the bigger logs to burn. Denser layers in the snowpack are less reactive themselves, but like the heavy fuels, once triggered, may increase the magnitude of the event. Often a small slide will "step down," triggering a deeper layer and a much larger avalanche. This is mirrored in the way a hot ground fire in the grass and litter will "ladder" to the lower limbs of the trees with the fire climbing into the crowns of the trees, resulting in a very destructive event.

I gaze at the inviting powder stretching out below my ski tips and contemplate the myriad variables involved in the tenuous balance of stability and entropy. As effortless turns float by and powder fills my consciousness, I'm happy that these mountains don't feel like shedding their skins today. At the bottom I'm overpowered by the euphoric balance of earth, sky, and water that is powder skiing, and give thanks that this season doesn't require me to hump a chainsaw back out to the road.


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