Avalanche Safety - Compression Test
Winter is coming and I’m already excited for some great backcountry ski touring. A topic that is always important in this regard is avalanche safety. I highly recommend to take an avalanche safety class with a good instructor. You will learn a tremendous amount of potentially life saving information, especially if you plan to do unguided trips.
I was always fascinated by the tests in the field. Based on one of my latest avalanche safety course these are no longer tought as they are regarded to complicated and provide only value to the trained person. For Switzerland and Austria for example you get so detailled snow saftey bulletins (slf.ch for CH) that one could really question the value of these personally done tests. Never the less I would recommend to use all the information available in the field as we all know conditions can vary. I personally would never assume a slope to be more secure than the bulletin states based on my own observations, but I might take less risk and ski more defensively if my tests indicate a higher risk of triggering an avalanche than the bulletin would make me believe.
How do you run a compression test?
There are a number of interesting videos on the Internet on this topic. One of the more interesting ones I would recommend is one by G3: Optimize your snow profile pit.
Unfortunately, these videos only show you how tu run the test. But how do I read these test results and what does it mean for me on that specific day? Is a break in a weak layer after 15 taps a good or bad thing? Can I still ride that slope?
Compression test interpretation
I’m not an avalanche expert, so I would be very hesitant to provide guidance here. But I did find an very interesting video and research study in this regard from the University of Calgary “Applied Snow and Avalanche Research”. In the linked video, Bruco highlights some very interesting results on a study they performed linking the taps and fracture character to the likelyhood of a skier triggering an avalanche.
Linking the compression test taps with the fracture characteristics does provide some actionable guidance on how avalanche prone a specific slope is for skiiers. Start looking for the two most critical fracture types being sudden collapse (drop) and sudden planar (pop). These two in the easy (up to 10 taps) and moderate (11-20 taps) are the most critical ones - likelyhood of triggering an avalanche are in the 50-60% range for easy and 40-45% range for moderate. Even up to the hard (21-30 taps) section they have likelyhoods up to 30%.
These are interesting figures to me, the applicability in the field has to be tested in the upcomign winter. Digging a good snow pit takes time. To be meaningful you should do it several times and in representative areas (i.e. slope). One always has to be careful not to put oneselfes in danger for running this test.
Once again, I highly recommend you to do an avalanche safety training - or also do a refresher if yours is more than a couple of years old. I’m not an expert at all but did find these research results interesting and worth sharing. Safe skiing.