Two skiers triggered a R2D1.5 avalanche in Central gully at approximately 2:30 in the afternoon. The previous night 2.9 inches of new snow fell on the summit with strong winds. During the morning and through the day this snow was transported into the deposition area below the Central ice bulge. Both Tuckerman and Huntington Ravines were under a General Advisory identifying snow stability concerns in isolated snowfields in each of the ravines.
In the words of skier #2: ” The sky was mostly clear with a lot of blowing snow, which should have been our first sign of newly loaded snow in the gullies. We moved our way up the hiking trail through the fan of the ravine carrying our skis on our packs. Halfway up the fan we broke left onto the snow fields in front of Pinnacle buttress and gully. Here we turned on our beacons and did a beacon check to make sure our transceivers were working in transmit and search mode: they were and we read in each others distance from one another approximately the same. With the high winds, cold and strong gusts, we decided to dig multiple quick/hasty pits as we ascended the snow. We found a lot of spatial variability up the slope. Scoured old icy surface, very dense heavy 2″ slab, 8-12″ lighter slabs, some of these slabs were right on old surface and some were sitting on top of what seemed to be consolidated snow. The cold temps and the winds were not friendly to digging more comprehensive pits, something we should have used as a sign that it was “not a nice day to go skiing” but we pushed on to the Central buttress where we found a large patch of recently (and still being) deposited snow. At the base of the ice route known as Cloud Walkers we began inspecting this new and different snow and kept digging around and feeling for layers in the snow as we climbed. There seemed to be no inconsistencies in this wind slab. Punching ski poles and our arms up to our shoulder we found the same type of snow as deep as we could determine with the assessment/observation technique we were utilizing. Climbing through this area of snow, postholing up to our waists at times, we made our way to the base of the ice slab in Central gully and tucked ourselves away into the corner of the rock climb known as Mechanics Route, which ended being a very good idea in retrospect. ”
The first skier started out and after one or two turns triggered a slab avalanche that carried the skier approximately 500 feet down into the fan, over snow, and fortunately not into the talus. The seconds skier standing along the buttress (skiers right) was not caught in the release and was able to move down the slope to help.
Skier#2: “I hurried down to a flatter spot where I left my skies and poles, pulled out my beacon and turned it on to search mode pointing it in the direction my partner had been swept toward. Taking a moment to make sure the beacon was indeed in search mode I found no signal, he was still too far away down hill. I began moving down through the rock fields, more or less on the hiking trail, adjacent to where the slide had flowed past. Visibility was difficult at a distance but I could see the debris from the slide. Most of it had been broken into small chunks of snow and some were still basketball size. I quickly moved downhill in a straight line scanning left and right to try to pick up his signal. Looking back and forth from my beacon to the direction I was heading, I soon saw a figure about five hundred feet below me moving from where I saw the slide go toward to where I was heading in the rock fields. It seemed to be my partner carrying his skis to a safer place away from the slide area.”
Snow Ranger doing a quick check on crown height.
In our experience looking at avalanche accidents and close calls on Mount Washington over the years, constant themes, mistakes, and oversights arise. Many of them are related to human psychological factors, the mental drivers that whisper over our shoulder “..everything is fine, good ahead you’ll have fun, you’ve done this before…”, while others miss the bulls-eye data that Mother Nature is offering and not having as much avalanche knowledge as we all should. These are traps any of us can fall into, which highlights how important it is to approach avalanche terrain with skepticism and keep asking the critical questions.
In this particular case a number of things were done well and some factors were overlooked. Good partner accountability and the ability to be support for our fellow partner is always important. Sound rescue skills and a level head to execute under duress is what all of us want in our mountain team. Beacon checks, going one at a time, good rescue execution are excellent practices and are commended in this case. Having a good plan in case of an incident is critical, but focusing on and planning for rescue should not take a front seat to all the actions we should consider in order to not get caught. It’s all about not getting caught, not avalanche rescue. New Hampshire leads the nation in the percentage of avalanche deaths resulting in trauma. Based on our terrain and low snowfall an avalanche can often send you through the trees and rocks. This results in a higher probability that you’ll be deceased when the snow stops more than any other state. The avalanche beacon is of little value in this scenario. So, avalanche rescue skills and gear are always extremely critical, but never more important than knowing how not to get caught.
In hindsight our vision is 20/20 as we ask ourselves “how could we have overlooked these clues?” This is especially true with the objective facts we would expect to ask ourselves. How much precipitation did we receive in the past 24/48 hours? What direction are the winds and at what speed? Is my intended terrain in the lee? Do I have the slope angle and adequate bed surfaces for avalanche potential? All these taken together will often send up some red flags. After these questions are answered you’ve got some data, now what? “What’s the stability like.” Snow pits and stability tests can be a double edged sword. They are critical to have an understanding what is going on under the surface. Stability tests such as Compression Tests, Extended Column Tests, the Rutschbloc, etc. give you some indication how slopes might react as opposed to quick hasty digging (sans tests) which can bring out red flag layers or crystals, but are limited in what they tell us about how the slope might respond to your load. The other edge of the sword in doing stability tests is they tell you what is going on right there and not accounting for potentially vast amounts of spatial variability. As this team went upslope they recognized variability which led to a choice to not spend too much effort or time in one pit which is not an unreasonable decision. There is a possibility that numerous pits would lead them to believe skiing the slope was a reasonable proposition. In our terrain spatial variability often increases the odds of “false stable” results when doing stability tests on a particular slope. Basically, stability tests can lead you to believe a slope is stable when in fact it’s not. No matter what mountain you’re on around the world knowing what’s buried 10-20 meters out in the middle of a couloirs is often the 64 thousand dollar question.
In this case, as best we can surmise, the initial fracture leading to failure occurred in a very thin section of the slab over water ice unseen from the surface. It is very probable faceted snow sat between the ice and the thin slab (+/- 15-22cm) causing a failure back into the deeper slabs behind the first skier. Given the same weak layer your “impact bulb” causes more stress on a shallow weakness than a deeper one. The thicker a slab (i.e. +/- 80 to 100cm) the more it generally distributes your load over a broad area on a weak layer. In a thin slab (i.e. +/- 10-40cm) a point load of the same weight impacts the weakness with a greater amount of pounds per square inch generating a more likelihood of fracture and failure.
20 hours after the incident two crown line profiles were done in a +/- 12 meter section of the 30 m overall crown length. This section was fairly consistent at 90cm deep before tapering rapidly after a rock in the crown. A score of CT11 with Q2 shear occurred in both profiles failing at 90cm. Although a number of layers existed above the test failures at 90cm they survived the CT11 tests.