COLD COUNTRY OBSERVATIONS SNOW-WELLS

We spent a part of the Christmas season in Bennington County, Vermont at our place in the Green Mountains. We arrived with the snow which was falling on a base that was well over a two feet. Big piles lay all around the house and roof avalanches kept our little dog Milo growling deep in his chest all night as big sheets of snow slid off the steep roof. In the morning, I noticed the trails of deer which meandered out of the woods and through our little meadow toward the house. They led to the place under our high, back-deck were little snow had accumulated and where patches of withered coltsfoot still struggled to stay alive in the damp soil there not far from the seep which drains off into the brook. Later that day, when I investigated, I found that the deer had eaten the partly frozen and curled up coltsfoot leaves and stems. The damp soil frose into crazy lifted soil of fractured lumps raised by the artic cold air that came down on us after the big snow fall. A few nights later, a lone coyote crossed the old deer tracks, its big dog-paws trended in a nearly straight line, not like a dog's, but more fox-like and disappeared into the woods on the far side heading down slope toward Flood Brook. That morning, I followed them a good way into the spruce and balsam woods with Milo struggling to keep up in the deep snow. Milo got tired and took refuge in a snow-well that formed around the base of the big maple tree on the edge of the meadow.

These depressions are interesting features of the snow country. Up here the locals either don't know what they are, or can give you a long list of theories of how and why they form. Milo didn't care what they were or how they got there, all he knew was that his big under-belly danglers were taking a beating in the cold crusty snow and they found welcome relief in the snow-well where he sat in the sun with his back to the base of the tree and his pink tongue lolling as he recovered from his exertions. He had to be strongly encouraged to leave his refuge.

These features which might be characterized as radiation tree wells, develop as depressions around the base of trees after the snow cover has been in place for a few days. They are generally deeper and wider on the south-side of the tree. They are apparently the result of the fact that as the dark tree bark absorbs solar radiation it re-radiates it outward toward the surrounding snow. Snow is an excellent reflector of sun's rays, as anyone knows who has been skiing on a sunny day, but on the other hand snow does absorb the long wave (heat) radiation from warmed bodies like rocks and trees. This heat causes the snow to sublimate (change from a solid to a gas) away and slowly retreat like an expanding collar from the base of the tree, while the surrounding areas exposed only to the sun's rays (which they reflect) remain unaffected.
In addition to the solar effect, there may be another source of heat which can cause radiation tree wells. That heat is derived from the earth itself. The trunk and roots of a tree-may conduct earthheat through its roots to warm its trunk and this heat may radiate out to sublimate surrounding snow. The tree roots are buried in the ground well below the surface where the earth is warmer can conduct heat upward. Ground temperatures increase from the surface downward, where at some two meters or so the subsurface may reach temperatures which average of about 45 to 50 degrees Fahrenheit in our latitudes. That is why the groundwater which seeps up and keeps that coltsfoot alive even late into winter under our back deck--its warm. Relatively speaking, this may be quite warm, perhaps 50 degrees above that of the air temperature during the depth of winter. That heat being conducted up through the root into the tree trunkcould well cause some of the observed snow-well effects around trees during periods when there is little sun to warm the tree base. In addition this would explain why trees develop well defined hollows around their bases but similarly exposed rocks and erratic boulders do not exhibit the same effect.

I am planning a test of this earth radiaton hypothesis here in the Greens by measuring the tree wells around the bases of deeply rooted vs shallow rooted trees. The hypothesis would be suppported if the more deeply rooted trees were found to have larger deeper tree wells. So far, snow and observation conditions have not enabled me to gather sufficient data, but work is in progress.

In among the evergreen forest on the upper slopes of Stratton, Magic and Bromley here in the Green Mountains very heavy snows sometimes produce enormous deep tree-wells in ungroomed areas around the base of tall, spire-shaped balsam firs or black spruces or other similar shaped coniferous trees. These deep wells may be dangerous to off trail skiers and snowboarders particularly during and after major snow storms. These large tree-wells, some in or western mountains have been reported at 20 feet or more, fall into a class I will term "snow void" tree wells to distinguish them from the small radiaition wells described above.

"In December 2007, a snowboarder at Mount Hood Meadows in Oregon suffocated fifteen minutes after falling head first into a tree well, despite efforts by three of his companions to free him. On December 22, 2007, at the grand opening of the Revelstoke Mountain Resort, an Edmonton ski instructor disappeared on the mountain's Jalapeno run. His body was found in a tree well three days later. During winter 2008, two skiers at Steamboat Ski Resort in Colorado fell into tree wells and did not survive. One was a man in his mid-60s and the other was a man in his mid-20s. The younger man was unable to escape despite assistance from two friends." http://en.wikipedia.org/wiki/Tree_well These fatalities have been termed "fatal non-avalanche snow-immersion deaths". The risks of such non-avalanche snow immersion fatalities are increased when the size of the tree well is very deep and probably more importantly when the skier disturbs the snow accumulated on the tree and is buried deeper by this latent fall of disturbed snow.

Deep snow-void tree wells typically form around the base of evergreen conifers such as balsam firs and black spruce during major snow events when fine snow falls for long periods in light wind (or in shletered areas) permitting the dense evergreen branches of these spire-like trees to catch and accumulate the white stuff on their close-set branches rather than permitting it to accumulate around the base of the tree. In effect, the snow that would have accumulated on the ground is visible on the branches of the tree. The skier can roughly visualize how big of a snow-well maight be found within the lower circle of branches of the tree by siZing up the amount of snow trapped on the branches. Trees that appear to be small and to have the outter perimeter of their branches touching the snow may be more dangerous. These "small" appearing trees may actually be average sized trees which are buried deeply by snowpack and they may thus have a deep snow well around their base. Another factor to consider is that the tree-well is often deeper on the down hill side of the tree since gravity tends to cause snow to creep down-hill and partially fill the upslope portion of the well.

Milo and I headed back to the house, retracing the way we had come. Milo closely followed the trail the coyote broke through the deep snow. As we walked back, I thought of how beautiful the snow is--- and how dangerous it could be. I determined to get out again and make some good photographs of radiation tree-wells. Then thinking of the dangerous snow void type of tree wells I formulated a mental promise to warn the skiers in my family about sking too close to trees in deep snow-pack up on Bromley and Stratton. Just one wrong turn, cutting an edge too close to a beautiful white-blanketed balsam fir and you could fall in head-first into a deep snow void to find yourself gasping for air, as you grapple at loose snow which falls away and collapses under you, while you breath in fine, white powder rather than air. Ugh! I shivered at the thought, as I finally reached the warm house and gladly stompped off the white stuff off still clinging to my boots.