We have had some significant temperature swings the past couple of weeks and so I thought a post discussing the effect this can have on the snow pack might be in order. 

Most of the time when we hike in the winter, we are hiking on trails that others have traveled before.  The snow gets compacted, rocks get buried and the trail actually gets smoother than it might be in the warmer weather.  This is ideal winter hiking and there is nothing like it.  You can sometimes walk on these trails with bare boots or light traction such as Microspikes, and sometimes you might need small snowshoes or crampons.  I often have both snowshoes and crampons with me on a hike because conditions change with exposure and altitude.

When the snow has not been walked on very much, or if it is a new deep snowfall, the snow is called unconsolidated.  Unconsolidated snow is not particularly dangerous to traverse, but is can be extremely arduous for one to do so.  Even with large snowshoes, hikers will sink deep in unconsolidated snow and the lead hiker in the group expends great effort to lift every snowshoe laden foot out of the footprint he has just made and place it in front of him for the next.  Often, on unconsolidated trails, groups of hikers take turns “breaking trail” so that no single hiker gets more tired than the others.

Because it is such slow going when hiking over trails of unconsolidated snow, one should keep in mind that the distance they can travel will be greatly reduced and trips should be planned or changed accordingly.  One of the biggest problems winter hikers have is that they have a particular goal in mind and lose sight of the time and the distance they have traveled or still need to travel.  There was recently a tragic outcome for a hiker as he ventured, unguided, up to Bondcliff on a winter hike.  He called his parents from the summit at 7 pm, much too late to be up there, 7 - 8 miles from the trailhead.  He unfortunately did not survive getting out and search and rescue teams had to call in a helicopter to retrieve his frozen body two days later.

Another thing to keep in mind when traveling over unconsolidated snow is that one needs to stay on the trail.  Often, especially as one gets high in the peaks and the snow pack gets deep, spruce trees get partially or completely buried beneath the snow.  These trees can have large air pockets next to their trunks where the branches have kept snow from falling and they create pits we call “spruce traps” which can be a hazard for the unwary hiker.  By being aware that these traps can exist next to spruce trees, one can safely avoid them all together, but having equipment, just in case, to extricate a hiker that has fallen into a trap can be important.

Sometimes we hike in areas where there may be large fields of snow below or above us.  In these instances, we must always be mindful of avalanche danger.  This is where the large temperature swings I mentioned at the beginning of this post can be important.  As snow falls, because it doesn’t melt, it accumulates in many layers.  Some layers can be just an inch or two, and some can be feet deep.  As long as the snow remains snow and doesn’t melt and turn to ice, these layers combine with one another and cohere.  This is a strong and stable snow pack and can be traversed safely.  However, when there is a freezing rain storm, sleet or grapple (a soft hail like precipitation), or the snow melts a little and re-freezes, a weak layer can be formed on top of the compacted base.  When more snow falls on top of the weak layer, or it is blown there by wind, it is a recipe for trouble.  The new snow on top of the weak layer is called a slab layer and may be one layer of snow or several, but the key is that it did not bond with the snow below the weak layer and so, when there is a triggering event, this slab layer of snow sloughs off and forms an avalanche.

The wind and weather can both be avalanche triggers but, by far, the most common avalanche triggers are humans.  Hikers, climbers or skiers on, or above, an unstable slab can add just enough extra impetuous for the snow to release and start to slide downhill.  Sometimes, hikers below an unstable slope can trigger and avalanche upon themselves just by the chain reaction of breaking the weak bond below the slab layer.  The key to hiking safely in avalanche areas is to avoid them entirely.  Before hiking in areas of avalanche danger, check the avalanche conditions board in Pinkham Notch or go here: http://www.mountwashingtonavalanchecenter.org/advisory/ to see the currently posted conditions.  Conditions are rated one of five different levels and the warnings on line generally will tell you what is safe and what is not.

There is a lot of fun to be had in the mountains in the winter, and they can be absolutely gorgeous, but it is important to explore them safely.  Be mindful not just of the weather for the day of your hike or climb, but also of the weather for the past few weeks.  With that in mind, the proper attire and an adventurous spirit, you will have a great time!