Overcast with rain in the morning, but mostly holding off over town during the day. Windy with temperatures in the lower 50s.
Yesterday at the concert I heard from someone that Medveie Lake was much lower than normal. With temperatures warming and the forecast calling for rain, I didn’t figure it would stay that way.
Despite the forecast for rain, I wanted to see the low lake level enough that I packed up rain gear and headed out.
I stashed my bike after the 20+ minute bike ride from Herring Cove to Bear Cove. At the crossing for the trail, Medvejie Creek was not running at the surface (no surprise) so no wading was required. I made it to the lake in a little over 20 minutes.
The lake was far lower than I’ve ever seen it. When Connor and I came up last March, it was not high enough to flow out, but it was at least 6 feet higher than what I saw today.
I walked the north shoreline to the upper end, and then came back along the south shoreline. On each side there was one location where I had to go up off the shoreline briefly to get around vertical rock faces that went into the water. The north shore was significantly easier, mostly due to the gentler slope. The steep shoreline on the south side required much more climbing/scrambling over and around boulders (plus a vague concern about how stable the rocks were).
I had previously realized the lake level rose around a foot (probably several feet) sometime in the last 100 years. There’s an old Merrill Photo that I tried to replicate. I found the tree, but it was just a snag with its base in the water. One thing that surprised me today was how many stumps that had pretty clearly grown where they sat were significantly lower down on the exposed shore.
In at least one instance, stumps were at a place that they could only have grown if the normal lake level was about where I saw it today. It makes me wonder how old those stumps are. Certainly more than 100 years. [I later realized the Merrill tree also had roots that dropped down to the lower level, so I think the 7-8 foot rise in water level may have happened in one or more events after Merrill’s photo (which was taken prior to 1929, when he died) and mostly before the late 1970s, which is the earliest anyone I have yet talked to visited the lake.]
It’s interesting to consider how the lake level rose. Since it’s a lake, it wouldn’t be carrying significant sediment (other than wood, I guess) which could accumulate at the outflow. However, the outflow is rocky up to the normal elevation of the lake.
My guess is rock fall and/or debris flows carried rock from the sides down into the outflow. It’s flat enough there that water velocities would be too low to move that rock downstream. Anything that came in further downstream I expect is regularly moved further down in high water events.
Last year when I was observing for a project at Medvejie Hatchery, the folks there told me that since a log jam broke loose in 2020, heavy rain events have seen faster rises and falls, with higher flows, and more sediment (including good-sized rocks moving down stream. The logs presumably provided a damping mechanism which allowed Medvejie Lake to rise a bit higher than it would without them, and so hold more of the big pulse of water in the lake to be released over a longer period of time.
Perhaps a rock fall/debris flow happened sometime after Merrill got his photo. Subsequently logs got caught up on it and formed the extensive log jam that was there from well before the first time I visited (early 1990s) until it blew out. It’s also possible the logs were already jamming up and helping to catch rocks coming down from the hill slopes either side of the creek.
Going further back in time, I guess one large event or a series of smaller ones would have built up a rock dam at the mouth, raising the lake level. It’s hard to imagine quite what it would have looked like, but maybe qualitatively not much different than it does now (since forest would have gone to the lake shore still.
Given the windy conditions making waves on the water, it was hard for me to be sure, but I think I saw one stump still in the water. Presumably it would be even older (assuming it grew where it sat).
Upon arriving at the upper end of the lake, another question came to mind. How long will it take for the lake to fill in?
Sediment (coarse and fine) coming down from the upper valley rapidly settles out once the stream hits the lake. The entire upper end was sand and mud, with many larger rocks that seemed fresh enough (and not even partially buried in sediment) that I suspect they were deposited by last year’s avalanches.
I haven’t revisited the area enough with this question in mind to get a sense of how much (if any) land has built up enough for vegetation to colonize during the last 30+ years I have experienced. I do know sand/gravel bars have disappeared and become covered in willows. However, those are right where the main creek comes in, and remain subject to being washed out during high water events.
That said, it does seem clear that last year’s avalanches deposited enough material that patches remain above the lake surface and will be colonized by vegetation in the coming years.
Looking back in time, this also raises the question for me of how much further back did the lake extend just after the ice left?
In addition to the filling in from the upper end, there are several places where streams come down along the sides. There are large coluvial deposits associated with some of them which are gradually pushing towards the middle.
The frequency of events bringing more fill into the lake vary, with smaller events mostly carrying cobble and smaller-sized rocks happening annually with heavy rain. Large events such as avlanches, debris flows, or significant falls may only happen every few years to decades.
Maybe someone with a better understanding and ability to model these sorts of events could come up with a plausible range. In the absence of that, I’m guessing it’s probably on the order of 1000s of years, and maybe more like tens of thousands. This might depend in part on how much more damming might take place at the outflow. Presumably if there is another ice age sometime in the future, the ice would scoure it all out (and make it even deeper than it had been on this go around).
Writing this up made me think of something I hadn’t considered before. The rock dam at the outflow could gradually be eroded from the lower end where elevation drops more rapidly back towards the lake if there’s not bedrock or larger boulders which keep water velocity down upstream of them. If I make it back up there again soon, I’ll try to remember to check.
One other thought/question comes to mind. I wonder if the north shore has a gentler slope because there has been more rock fall than on the north slow. If it’s subject to more free-thaw cycles due to sun, that would be a potential explaination. With a couple of exceptions, the rock on each side seems to be the same granodiorite. (There are two sections of different looking rock on the south shoreline, but the rocks there were smaller and the slope gentler than the rest of that shoreline.) On the other hand, avalanches may be more of a thing on the south side (north facing), and I’m pretty sure that’s what’s kept trees out of large sections.
With the lake so low, it was much easier to poke around looking for lichens, mosses, liverworts that grow right at the shoreline or in the shallows. I made many observations of each, especially on the north shoreline (before I started running low on time and paper bags).
I heard several Ruby-crowned Kinglets singing from the forested areas on my way around. I have yet to hear any in town, but maybe they were around today.
I wasn’t thinking too carefully when I packed to go. I put the rain gear in thinking I would probably end up in some heavy-ish rain. That was fine (though I did not end up needing it). I hadn’t eaten anything before I left, and didn’t pack any food. This also wasn’t such a big deal, though I would have appreciated food if I had had it. The bigger issue was water. At the very least I should have packed the filter/bottle that weighs very little. I was thinking more in terms of a quicker trip just going to the lake and back. I wouldn’t have needed water if that’s all I had done. The 4+ hours I took walking the shoreline were a different story. I did drink some water from a small water course coming into the lake. I probably should have had more.
My iNaturalist Observations for Today
Map-based Gallery view showing where many of the photos were taken