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Ron Simenhois and Karl Birkeland on demystifying the Extended Column Test

November 6, 2021

In this 'Demystifying Avalanche Concepts' post, snow specialists Ron Simenhois and Karl Birkeland dig into the details of the extended column test; how it works, why it's useful, and how they came up with it.

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Pit digging is a staple of any reputable avalanche safety course and a time-tested method for determining what is going on beneath a coat of freshly fallen snow. Pits are typically billed as a way to determine the stability of the snowpack in a chosen zone and help identify the likelihood of triggering a slide. But in 2006, two scientists took the snow safety world by storm by creating a new test that evaluates both crack “initiation” and crack “propagation.” Since then, the Extended Column Test has become a staple among avalanche forecasters, as it can provide clues as to how likely a slab avalanche (the worst kind) is to grow in size when it releases.

For years, Rutschblock, compression, or stuffblock tests were the primary tools used when digging a pit to determine the structural integrity of the snowpack on a particular slope. All these tests primarily focus on crack initiation, the telltale sign that a weak layer has failed. But in 2006, Ron Simenhois, working then as a ski patroller at Colorado’s Copper Mountain and New Zealand’s Mount Hutt (but now an avalanche forecaster at the Colorado Avalanche Information Center), and Karl Birkeland, an avalanche scientist with the USDA Forest Service National Avalanche Center, presented the idea that there needed to be a test to measure crack propagation as well. Propagation means that the failure extends away from the trigger and the avalanche becomes a dangerous “slab” avalanche instead of simply a loose snow avalanche or “point release.” 

While the accuracy of a properly conducted compression test is crucial, the downsides of a test like this are also significant: many minutes spent in the cold and the need to have a pit on the slope in question that poses its own danger to the digger. Another major downside to traditional pit tests that Simenhois and Birkeland posited in their 2006 paper dubbed The Extended Column Test: A Field Test For Fracture Initiation and Propagation, is that while compression and stuffblock tests can identify weak layers with potential for crack initiation, they can also hide layers that are of greater risk for actual crack propagation that lead to an avalanche. 

So Simenhois and Birkeland dug in and decided to develop a test that could give the user a rough assessment of both the initiation and propagation propensity. 

“The extended column test aims to test the likelihood of crack initiation and subsequent propagation by extending the size of the loading area,” stated Simenhois and Birkeland in their 2006 ISSW article. “The extended column allows the slab to transmit stress across the column, and we assume that cracks that are initiated will quickly propagate across the column if conditions are favorable for crack propagation.” 

This is done by digging a column that is 90cm across and 30cm deep (into the pit wall) that is isolated on each side. To conduct the test, you then use a similar tapping technique to a compression test: 10 taps that are initiated at the wrist, 10 taps that are initiated at the elbow, and 10 taps that are initiated at the shoulder. The goal is to see if a layer of instability fails and if this crack then moves across the column you have created. 

When Simenhois initially presented Birkeland with his ideas for a new test, Birkeland recalls being excited by the concept. “I thought, ‘this will be a really interesting thing to look at,’ so I said, ‘Well, Ron, have you collected any data on that?’ And, Ron's response was typical Ron. He said, ‘I have 243 different snow pits with these results and avalanches nearby.’ And I was really impressed and said, ‘That works pretty good for me, Ron, can you send me that spreadsheet?’” 

About the initial reception of the paper by the avalanche safety community, Birkeland explains that people were enthusiastic about the possibilities the Extended Column Test presented because of its relative simplicity to conduct and to interpret the results. Unlike other tests, the Extended Column Test requires fewer steps, which makes it more intuitive to dig and analyze. 

Simenhois reiterates the usefulness of having a pit test that can be performed rapidly and notes, “One of the things I like about extended columns is that they are quick tests. It's not a lot of work, and it gives you more time to ski or to look at the snow in other places.” 

But he explains that like any other stability test, there still needs to be a degree of discernment in choosing where to conduct an ECT that effectively represents snowpack structure. He describes his common pit digging process: “I try to dig pits in places where I think the snow is shallow enough for crack initiation and deep enough for crack propagation. I go through those transitions. I try to go in with an idea of where are those areas that are less stable or are more likely to get unstable results. And then as I do that, I try to dig a pit where I can see those more unstable areas, or at least where I think there are going to be instabilities based on slab thickness and hardness.—That's where I'm going to go to dig a pit.” 

Both Simenhois and Birkeland agree that they primarily use pits to confirm what they have already guessed about the stability of a slope based on conditions, snowpack history, and avalanche forecasts. “If there are other signs that point to the slope being unstable, you never want to use any field test to justify going into avalanche terrain,” Birkeland said. “Rather, use these tests as the last check when other signs suggest the slope may be stable.” 

“I use it mostly as a no-go sign,” Simenhois explains. “I am not necessarily going to ski the slope if my Extended Column Test doesn’t propagate. I have many other things I take into account, but if my test does propagate then I typically will not ski the slope. I'm just going to go and find a mellower slope if I'm worried about it and especially if I get a propagating result.”

What’s the take-home message from this groundbreaking research? That the likelihood of a failure turning into a slab avalanche is just as important as its likelihood just to get started. Better to figure this out in the pit rather than on the slope. It’s a little too late once you see those “spider cracks” shooting out from beneath you.

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