Glide crack

Another similar spot exists on the South Face of the West Peak of Goat Mountain and can easily be viewed from the Mt Baker Ski Area. Every year an enormous series of glide cracks opens up and eventually it collapses. I beleive the surface is rock slab.

Good discussions on the WR glide crack and ensuing avalanche &#8230;lots of good knowledge out there for sure. I&#8217;ve watched, monitored and thought about this or similar cracks for many years and wanted to add a little more to the previous comments.<br><br>The glide crack and resulting glide crack avalanche on WR that's being discussed is definitely an annual occurrence, and I believe that its release in this instance most probably stems from a variety of factors, including weakening of the slab itself (faceting) and some lubrication of the underlyinbg bed surface/rock face. The physical constraints here include the facts that much of the slab lies on a steep and rather smooth rock face (with some heather, grass and other small shrubs near the boundaries), and a significant rollover near the top of the slab boundary that amplify stress concentrations affecting the slab and produce the initial glide crack near the top of the rock face. Once formed the slab is held in place by flank (shear) strength and compressive strength at the stauchwall, along with basal shear strength at the snow-rock boundary under the slab. One possible scenario is that during the past week or so of cold weather, temperature gradient driven faceting slowly weakened both flank and compressive strength of the slab. Then slowly rising freezing levels and some warming/sunshine Sunday and Monday on south facing terrain produced increased creep and glide of the slab itself, solar induced snow melt at the rock, and associated lubrication of the shear interface under the slab. All of this may have initiated shear failure between slab and rock which then put too much stress on the weakened flanks and stauchwall of the slab (stress exceeds strength), resulting in subsequent fracture at the remaining slab boundaries and the pictured avalanche. Certainly the mud shown spread over much of the slide indicates that melt may have been an important contributing factor. <br><br>One of the main points here is that you don&#8217;t want to wander around on slopes under glide cracks during changing weather regimes, for any changes in the thermal or mechanical regime of a slab under duress do not normally result in good things.<br>

Wow! Cool photos and discussion.<br><br>That slide is pretty close to the site of the old Wellington disaster. As I vaguely remember, the Wellington site is a bit farther down the valley. But I'm not sure about that. Anybody know for sure?<br><br>The Wellington disaster was caused by a different set of conditions, but it's interesting to have this modern reminder of the dangers of Windy Ridge.

Hey Lowell-<br>To the best of my knowledge, the Wellington slide of 1910 occurred in the almost unassuming path just to the west of where the two drainages fork--which puts it to the east-northeast of the Windy Ridge glide crack that's being discussed. It's the path that does not have and did not have the "protection" of the railway snowsheds back in the early days before the tunnel, which is one of the reasons that the train parked where it did (no trapped smoke in the shed from the locomotive). And since it has a lower starting zone angle than many of the paths further down valley that often run at least once or more annually, it was perceived to be less dangerous...

To the best of my knowledge, the Wellington slide of 1910 occurred in the almost unassuming path just to the west of where the two drainages fork--which puts it to the east-northeast of the Windy Ridge glide crack that's being discussed.

<br><br>Having looked at a map, I think you're right. Here is a topo map of the Wellington vicinity. A few years ago, Garth Ferber and I walked down the Iron Goat trail to look at the 1910 avalanche site. As I remember, there are memorial markers in the snowshed shown on the map, a few hundred yards inside the east entrance. The snowshed was not there in 1910, but was built later. I think the avalanche ran down the SE facing slope directly above the snowshed.<br><br>Can anybody identify where the glide crack slope is on this map? I think it is the slope NW of the word "GRADE" along the old rail line.

I've watched that particular glide crack for years and most years it slides just like this one. If you really study the slope during the summer, there is kind of a steep carved out half shell on the face that begins where crack is. Below where the slide starts is a big pile of rocks just below the big bowl. It's really an odd looking feature. Maybe water forms a pool somewhere under there creating some conditions that prevents good anchoring early in the season?