In Colorado this spring there was a pattern with the kind of avalanches people have been getting involved with: dry snow avalanches in a spring context. There are a couple nuances with this specific setup that can help us operate more effectively in the spring.
First let’s bring it back to the fundamentals of new snow settlement.
When new snow falls, it has an inherently unstable grain form. The stellar dendrite—the perfect snowflake—is predisposed to settlement. The large surface area to volume relationship in the shape of a stellar is fundamentally unstable and immediately it begins to deteriorate.
Soon as it falls the stellars begin to decompose into a more stable shape with a better surface area to volume relationship on its path a ‘rounded grain’. As they deteriorate, they begin to form bonds and loose pore space becoming more dense. This process generally referred to as ‘settlement’ causes the new snow to begin taking on the slab like properties that allow fracture to propagate and avalanche conditions to evolve.
Settlement can occur faster or slower under specific conditions, generally hotter and more humid means faster settlement. For instance a storm that begins in the late afternoon–while it’s warmer–tends to bond more readily and settles in well as it progresses to cooler snow that night.
As the new snow is settling amongst itself it’s also beginning to bond to the underlaying old snow. This new/old interface is one of the keys to dry snow avalanches being so reactive in the spring.
Snow likes to bond to like snow. The more similar the characters of a grain the more rapidly it tends to bond. This means that new dry snow can bond out very effectively on a old surface of relatively new snow and decomposing fragments. Sometimes this can be only a matter of hours. In the case of spring snow surfaces composed of crusts and melt forms, the new dry snow does not bond well at all.
So not only do we have old snow interfaces that don’t allow new snow to bond but we are dealing with a much higher hotter sun. This heat leads to rapid settlement in the new snow. This combination leads to surface avalanches with rapidly growing snow volume as well as dramatic spikes in reactivity with only a short amount of sun exposure. This combination makes it easy for snow volumes to grow rapidly as every small avalanches immediately entrains all the new snow available below them as they run.
Solar aspects with seemingly small snow volumes can turn into fast ticking time bombs as the sun warms them up. It’s easy to find parties booting up a solar couloir at around 10 am as the snow quickly transforms from a few inches of low density stellars into a large loose snow avalanche as the sun hits the slopes. The resulting flows can catch people off guard because it’s hard to achieve similar snow volumes from entrainment in the winter.
In these conditions I tend to prefer shaded aspects as the new snow settles slower and grows a slab more slowly as well as bonding with the underlying old snow of a similar character much faster.
The other option is to enter slopes from the top, as these problems are very manageable before they grow in size during their flow. Managing six inches of snow in this character from the top is very reasonable, but that same avalanche will quickly have an unmanageable volume after a short flow, be it naturally triggered from the sun or human triggered by another party.
Know Your Guide:
Always remember to be critical who you get your avalanche education from. There are a lot of uncertified guides with limited experience in the industry out there these days. At minimum seek out a AMGA certified ski guide or a IFMGA licensed mountain guide for your backcountry education.