Helon and I took advantage of a warm sunny day to get up into Tuckerman. Our primary objectives were to look at the existing snowpack and get a handle on what today’s danger was, for anyone coming up later today, and for what the emerging heat wave might do to the snowpack.
For those few who came up today, they were rewarded with good stability in Right and Left Gully, but different conditions. Left Gully’s snow stayed cold and dry despite the +7C ambient air temperature. In one location, Helon found a thin 4F+ slab layer sitting on top of a loose graupel layer with very easy compression test results. Snow test results don’t always tell the whole story though. Helon’s impression was that the Moderate rating was appropriate. One of the skiers in the gully tested the slope with a finely executed faceplant, which is often a more realistic test of a slope’s stability than compression tests. (I’d name names, but the Harvard caretaker might not want his identity revealed.)
Right Gully had a much different environment than what was found in Left. Rather than cold dry snow, the surface layer was saturated with melted snow. At 11:45, the wet layer was 7cm deep. By 12:45, it was twice that or more. The loading that came in with yesterday’s 5cm snowfall didn’t create much new slab in Right, so my earlier concerns regarding stability of this layer were quickly erased as the sun baked the slabiness right out of the upper layer.
Standing in the middle of Right Gully for a long time, I began to look around at the terrain, and I realized that the snow I was standing on was probably 8-10′ lower than where it is in a typical winter. Trees whose tops are usually the only part visible were standing proud over my head. At the top of the gully, rocks that we see melt out sometime in early May have not even been buried this year. It really sunk home how poorly we’ve done for snowfall this year.
The 1F+ (hand hardness scale) slab in Right Gully was 100cm deep down to a hard, hard crust. The very top of the snowpack was wet snow from the heat and sun. Cooler snow was found down below, with a few centimeters of 1mm facets above the crust. I found it hard to really get a good look at the facets – the air temperature was +7C so as soon as I put some on a crystal card they began to melt. This facet layer gave two compression tests at CT21 and CT23. An extended column test did not propagate. I also got negative results with a shovel tilt test and shovel shear test on a suspected weak layer at 37cm down from the top. Generally speaking, these are good test results for the stability of the slope at the time the tests were done, but the facet layer is concerning for what might happen with further warming.
In the Sluice, Lip, and Chute, as well as the left side of the Center Bowl and in the hangfire, there is a good chance that the facet layer remains intact, and this might become reactive tomorrow or Thursday as the upper slab becomes wetter and wetter.
Here are some other pictures from the day:
I’m running out of time for this post now, so be sure to check tomorrow’s advisory for more information and stability ratings for the day.
Helon and I got up into Tuckerman early this morning and were treated to the sight of two fresh piles of avalanche debris and one older pile. With our avalanche eyeballs wide open, we welcome the arrival of the 2015-2016 avalanche season. The recent slides were likely from overnight or early this morning, as they were both very soft and had slightly different levels of wind effects on the debris. The older slide was probably from earlier this week.
The first of the recent pair came from the Chute. We believe all the debris came from the crown lines visible in the picture, across the narrows of the gully, into the variation to the lookers’ left of the main path, and down along the buttress. Debris from this was approximately 2′ deep, some less, some more. The crown ranged in size from a few inches deep to a few feet deep.
The second of the pair was from the far left side of the Center Bowl, just to the lookers’ right of the Chute. The crown was still visible beneath the ice bulge, although wind loading was ongoing and working to fill it in. This slide was a little smaller than the Chute, with debris being about 12-18″ deep and a max crown depth of 18″ (just a guess, as we couldn’t access the deepest location and it had been partially reloaded.)
Even though we hadn’t yet begun using the 5-scale danger rating system, these new slides were not completely unexpected. We were a little surprised at the size; I’d call them both D1.5R1, but they are at the larger end of the R1 size. The one that surprised me a little is the older slide that crossed the hiking trail down low in the flats. The trajectory of this shows it coming from the Center Bowl and left side of the Center. Based on how far it ran in lean conditions and weather history, it was likely a pretty hard slab.
After returning down to Hermit Lake, we got a report of another small avalanche triggered by a skier. This was in the area we call “Chicken Rock Gully,” which is the small terrain feature that fills in between the Open Book and Lunch Rocks, and from the top you can go right into the Sluice or Left into the Lip. The party triggered the slide near the rocks at the top of this slope. They reported that it was about 4-6″ deep, 40′ wide x 50′ long, and ran down to the bottom of Lunch Rocks.
Jeff Lane, Snow Ranger
Mount Washington Avalanche Center