Back on June 28, a large rockfall event occurred on the south slope of Hallett Peak, halfway up Chaos Canyon. My college geology teacher probably would have called it a “mass wasting event”. Mass wasting is simply the movement of rock or soil downslope due to gravity. In RMNP over the last decade, we’ve seen a number of these but most were due to flooding. The water loosened things up and gravity took over. This one, though, was not like those others.
Mountains erode over time. Generally, we think of erosion as being due to water or wind. Very little of it is due to wind. Erosion due to the normal, continuous flow of water isn’t that great, either, mostly just making jagged rocks round. Mass wasting, whether it be landslides due to flooding or rockslides like what happened in Chaos Canyon in late June, is by far the largest contributor to erosion.
Due to the rockslide, the NPS closed off access to most of Chaos Canyon above the lake. Obviously, things are quite unstable there and it’s entirely possible that more slides are in store. This closure doesn’t really affect me, as I’m not a rock climber. I’ve only been a significant distance up the canyon from the lake once when Ed and I hiked to the small, unnamed tarn near the head of the canyon.
It’s not the slide, though, that interests me. I’m interested in the glacial flour. Also called glacial silt or rock flour, glacial flour is the sediment from ground-up rock particles produced during glacial erosion. This stuff is very finely ground. The particle sizes typically range from 2 microns to 65 microns. Particles that small will hang suspended in water for a long time. (A human hair is around 70 microns thick, while wheat flour is in the 10-41 micron range.)
This glacial flour is what gives the turquoise color to lakes that are fed by glaciers.
Clear water absorbs longer wavelengths of visible light (yellow, orange, and red) and strongly reflects shorter blue and blue-green wavelengths. Therefore, unless there is another pigment present near the surface of the water, like algae, it will always appear blue or blue-green. The glacial flour that floats in the water provides reflects light back to our eyes and makes the water appear both opaque and bright. Interestingly, the composition of glacial flour absorbs most of the blue light and reflects some blue and green, as well as yellow, orange, and red (but, as mentioned above, these colors are absorbed by water). With the elimination of the colors absorbed by both the glacial flour and the water itself, what is left is mostly green and some blue light reflected back off the glacial flour to our eyes: turquoise. The more glacial flour present in the waters, the greener the water will appear.
There is no glacier in Chaos Canyon; there hasn’t been one for a long time. But it turns out that a significant amount of rock flour is released in these rockslides. There was a smaller rockslide here back in 2018. The lake changed color for a few months, but to a much lesser degree than right now.
I can’t predict how long the lake will have this color. It is my guess, though, that the water will be clear again next spring. Lakes fed by active glaciers are always being fled flour, but I doubt snowmelt will pick up more flour from this rockfall and so I expect the lake to be clear again in the spring.
Then: If I want to see the lake decked out in turquoise, I better go now.
Tuesday, September 13
Lake Haiyaha is only a couple of miles from the Bear Lake parking lot, so it’s one of the shortest hikes I take. And, being so close to the parking lot, the place is always crowded.
I followed the masses up the trail to Nymph Lake and Dream Lake. It was a conga line. The flip-flops and no-water crowd was well represented. Nearly everyone was talking. Some hikers on their way back to Bear Lake gave words of encouragement to those going up: “You’re almost there!” It amuses me that everyone seems to think everyone else is going to the same place they’re going to. In this case, “You’re almost there” meant Dream Lake, 1.1 miles from the parking lot.
At the turnoff for Haiyaha, the crowd thins a bit. I had three or four minutes where I could see nobody ahead of me or behind me.
Just before reaching the lake’s outlet, I head west to reach the northern shore of the lake. The trail dumps the crowd onto the boulder-strewn southern shore. To get to my spot on the quieter shore, I have to navigate a bit of talus and dodge downed trees, but it’s worth it. Even though nobody is over here, you don’t really get any solitude: sound travels surprisingly well over water. You can not only see the people on the other side of the lake, you can sometimes make out what they’re saying.
Sitting on my rock, enjoying a snack, I concentrated on my nearer surroundings. The water is translucent for only maybe six inches. Any water deeper than that appears opaque. I was wondering what effect the glacial flour has on fish, but I did see trout rise a few times. They can still see insects on the surface because of the shadow, and they’re now pretty much invisible to predators, so unless the flour interferes with their gills, the fish are probably doing fine.
I wanted to make my way to the top of the ridge between here and Dream Lake. I’ve been up there twice, once in winter and once in spring. There’s a really nice view of Haiyaha from there. I never made it. I was too far west when I started and never got more than halfway. I spent about twenty minutes in the attempt before capitulating and heading to the crowded side of the lake.
There’s a social trail that leaves the main trail just before the main trail starts crossing a rock pile. A few feet up the social trail, the Park Service has posted a sign showing the area of the canyon that’s closed. I worked around the south shore for a bit until I found a nice, flat, unoccupied boulder to sit and have my picnic lunch on.
Today’s beer: Great Divide Brewing Company’s American Lager.
On the way back, rather than return the way I came, past Dream and Nymph, I headed down the “back way” on the trail that goes to Glacier Gorge junction.
An interesting thing about Lake Haiyaha is that it has a leak. In winter, the lake drains to a level several feet below the level of the outlet. I’m not exactly sure where this leak comes out onto the ground, but this trail follows the stream formed by the leak for a short way, to where it fills a pond. The stream itself looks milky, and the pond is less green and more a milky, pale blue.
I’m happy I got to see the lake in this condition. The small rockslide in 2018 didn’t have nearly the same effect as this year’s big slide. Seeing the lake this color may be a once-in-a-lifetime thing. And, although I complain about the crowds, I think it’s great that so many people can enjoy the Park. Besides, it helps me appreciate my hikes where I get hours of solitude.
[See some of my older Lake Haiyaha photos here.]