Colchuck avalanche

If the link doesn't work, it's worth your time to look up Washington Hikers and Climbers on facebook to find this video.

www.facebook.com/banzaimf/videos/10154393776449181/

colchuck avalanche

It's a video of an avalanche taken by someone at Lake Colchuck looking up at the glacier. It was probably raining. I was north in Spider Meadows and there was a soaking rain that grew and decreased in intensity. Probably similar at Coluchuck.

Makes me shiver. I generally operate under the assumption that summer snow is safe. Clearly that isn't true.

I guess it was Saturday morning. Here is an even better video of the avalanche



instagram vid

Summer snow in the Cascades is different from other ranges as the quantities of snow are generally large, the elevations are pretty low, and the temperatures, especially at night are high. Same goes for glacial hazards.

Lots of water to lube up the systems.

Stay smart!

That would have been nerve racking to be near it. Shot from May, much different conditions, but to think that slope does move at times. Timing...

one more view from campers at Colchuck.



and here is a video from the climbers as the avalanche approached them. Would you have time to get out of the way? I don't know.
www.facebook.com/shane.flynn.3323/videos/533711566826926/

Did any of the observers note a trigger? Where was the crown? There's quite a bit of entrained rock/debris for a simple wet slide originating on the glacier itself.

From the comments from the poster of the Instagram video:
"A rock fall the size of a pickup truck is what caused the slide. The snow was not wet, it was firm."

Here is my hypothesis.

1. Rock falls from above (off Colchuck) and pierces snowpack


2. Snow at bed surface is rotted and provides inadequate resistance to stop the rock. Rock slides below the snow surface down glacial ice and then down the polished granite slope like a wedge or chisel. Rock goes fast and plows beneath competent surface snow, pulverizing it. Pulverized snow falls back to bed surface (behind rock) and slowly starts to slide down the slope inside the channel


3. Rock stops. Pulverized snow in channel slides downhill, hits rock, jumps out of channel and fans out.


If this was the mechanism, I'd bet that almost no surface snow below the channel was entrained, and that the entire debris pile consists of the snow from the channel. Also, I expect to find the big rock wedged in the snow pack at the end of the clean channel. 

Mike, Great theory; which is very likely the scenario that happened. Nice "engineering" sketches. It makes total sense to me and hope that is what happened and not a new normal because, if it was a rock induced event, it would be a rarer occurrence. Like others have said, the videos posted also put a "shiver" in my groin and your theory may let me breath a little easier. Will you please stamp the sketches.

Will you please stamp the sketches. 

I'll stamp them "the rock-mole hypothesis"
I plan to go look at it later this week. I'll report back what we find.

In the video, it looks a lot like I'd imagine a lahar to be. Rock gets mixed up with snow and ice chunks, which flow downhill in a slurry. It's impressive the amount of material moving down the Colchuck.

Have you guys seen the pictures of the Boulder glacier debris flow that occured this year on Baker/Sherman peak? That one also ran an impressive distance. I went and camped on Boulder ridge a couple weeks back and saw debris from that event below the toe of the glacier, near where the trail reaches the fixed rope up onto Boulder ridge. And the starting point for that flow was the top of Sherman peak.

Mike, add free flowing water into the mix...

Is there any history of glacial outburst flooding/internal water pooling on the Colchuck?

^ I was wondering that, too.

This event was after/during a rain saturation period, right? Full-pack wet-slab-on-rock release somewhere high up?

Considering the rapid changes we've seen (especially after last year), there may be no history of GLOFs, but that type of action may very well have played a part here. Interested to hear what people find upon investigation of the site.

GLOFs: en.wikipedia.org/wiki/Glacial_lake_outburst_flood

Mikes mole rock theory has been debunked! We went up there today(tr to follow) and "discovered the cause" there was a huge land slide on the Colchuck side that was the mechanism for the start of the release.  It really was just amazing, I wanted to torture Mike and his theory! HA!

He is require to submit a new "stamped" drawing to explained the new discovery.

The large amounts of water migrating downhill within the snow at this time of year is a big factor when something loads the slope like a big rockfall. Very persistent layers within the snow left over from winter can provide a base for this water to track along.

Mikes mole rock theory has been debunked!

I was way off. Here is we found:

The trigger was a huge rock fall from the shoulder of Colchuck.

colchuck col is at the left on the skyline. The green line is what I believe to be the event boundary. It's possible that the gap in the skyline did not exist before this event. I wonder if someone has a photo for comparison?








All the snow slid off the glacier on the steep pitch near the top. The bed surface is glacier ice. On the left side in this photo, the snow depth at the skyline was just more than a ski pole, and near the bottom of the slope the sidewall was just over 300cm deep. There was a weak layer between 155cm and 195cm from the surface where my probe met very little resistance. I don't think the weak layer played any part in this event. The snow depth tapered on the right, at one point to zero where glacier ice is exposed at the surface (right of center in the photo)


The debris pile was truly impressive. It filled a large portion of the flat above the terminal moraine. 15 feet (estimated) deep at the lowest edge.


I re-watched the videos. The woman from the lake mentioned hearing something and then a few minutes later seeing the avalanche. Her video shows white snow. The climbers videos both show white snow, especially the debris flow into the moraine basin which was snow chunks with an occasional large rock. What Jamie and I found in the debris pile was a mix of rock and snow with sand over the top.

Mike, WOW! Thanks for going to take a look with Jtack and reporting back; nice pictures paint a good story. It definitely looks like Mother Nature did an impressive job of "destructive-testing" on the snow pack. Gravity is a heavy thing and sure can do a great amount of work when a large object is released from a height. Its usually pretty calm and peaceful out there in the hills but, in geologic terms, some pretty awesome and powerful things happen regularly. May we all travel in guardianship...

Thanks for all the observations! Nicely done.