After a visit to the Columbia Gorge in the pacific SW a while back, I became interested in the Bonneville Slide, a landslide from circa 1400-1750 that actually blocked the Columbia river for a time, before the water forced its way through.
In studying maps of the area, I came to notice that in the runout area of the slide, there were quite a few lakes. Wauna Lake, Hazel Lake, Wecoma lake, and a handful of others too. They seem to be unusual for that area of the country, until I consider that they are all sitting on top of landslide material. I don’t see any streams that seem to drain them, so I’m guessing they seep into the nearby Columbia river via their beds, and stay replenished mainly by rain.
I’ve poked around on the net trying to find some geologic discussion about these associated lakes to see if my assumptions are correct or wildly erronious, but all I’ve been able to pull up are real estate and resort ads for said places. Can anybody explain the phenomenon of lakes forming on landslide detritus, or point me towards more scientific articles about these lakes? Or even tell me if the lakes have a collective name?
Looking at the map and as someone who lives in Portland and goes up around that area fairly often, you’re probably not far off the mark. There are about a kazillion seasonal streams that drain off the Gorge and quite a few year round ones as well. The area around those lakes does tend toward marshiness so probably what happens is that in summer the lakes drop a bit in volume then when the rain hits they fill up and the areas between the lakes and the river turn into vernal marshes and drain off that way. There aren’t a lot of trees out there between the lakes and the river, which does argue that the land is too wet for much of the year for trees to get established. Also, some of the lakes actually have managed to cut channels directly to the river either on their own or some have been been cut by people, probably to stabilize the land in the area.
Also, the area around there tends to be lousy with springs and artesian wells so there’s no lack of water to fill the lakes with.
I have no idea if there’s a collective name for the area, there’s no signage to indicate such. It’s a very pretty place though, and Skamania Lodge is quite nice.
Depending on the lake, some of the base level might be from ground water, but I think the bulk is rainfall and drainage from the hills. I wouldn’t say lakes are too unusual in that area; I saw one book that referenced 3,813 lakes and reservoirs in Washington.
If you look at this view of the area, it’s easy to see how the slide intruded into the original width of the Columbia at the Bridge of the Gods. Lakes could more easily form here because the area is relatively level compared to the steep slopes of the gorge, so there’s a place for basins to collect water. The slide could also result in creation of dams that block what were streams that formerly ran freely into the river.
The area of these lakes isn’t exceptionally marshy, compared to some of the other places along the river. If you follow the highway west about 10 miles, you can see Franz Lake, which clearly formed through sediment deposit from the river. You can see in satellite imagery that the area is more marshy. The lakes in the slide area in contrast are more heavily forested and above river level a bit.
I think most, if not all of them, do have some surface drainage into the Columbia. There are drainage pipes at a few places along Highway 14; I believe this culvert on the SE side of the highway is one. Wauna Lake appears to drain into Rand Lake, which drains into the unnamed pond immediately west of the highway, which drains into this culvert. I feel comfortable guessing there are many such culverts along the road - the engineers aren’t going to risk the highway and train tracks getting washed out every time there is a heavy rain.
I couldn’t find anything too useful on the specific geology and hydrology of these lakes, but there were a number of articles that came up when I googled “lakes formed by landslides”. The ones I glanced at talked more about the landslide creating a dam, not the lake forming in the landslide area itself, so it’s not exactly what you’re looking for. But I think the general idea is the same: an outlet is blocked or a berm is created, and the lake forms behind it. The mechanism is the same whether the basin was pre-existing or created during the landslide.
Plus, the landslide material would have been much softer than the surrounding rocky surface, allowing water to pool, then the weight of the pooling water would further encourage the compaction of the material underneath. I bet it was some ugly right after it happened though.
Apropos of nothing much, Merrill Lake is a great example of a landslide created lake–there are seven or eight big streams that feed it but only one that allows outflow and then only when the water’s quite high. I go kayaking there often, it’s a gorgeous lake and apparently the fishing is amazing though it’s a catch and release lake that allows no barbed hooks. Toward the end of summer the lake is considerably smaller in area than earlier in the year, with some marvelous sandbars cut by deep channels up at the northern end. The spiders parasail along the water with big wafts of silk pulling them along when the time is right, super weird looking.
Thanks for the education, guys! That helps. Lakes on landslide material is an interesting concept; in Wisconsin we have lakes in the formerly glaciated areas, where a huge block of ice was driven into the gravel from the glacier. And in some ways I can see how those lakes in WA are similar to our Kettle Moraine lakes.
When I saw the map linked to above, I couldn’t help noticing the ‘Bridge of the Gods’ across the Columbia River on it and pulled up a Google map of it. Very strange representation of both ends of it by Google! Sadly, Streetview shows that it’s not really that shape!
I grew up near there. I don’t recall there being a collective name for the lakes specifically. We just referred to the general area as Bonneville. My brother still lives around there. He’s much more up on local knowledge than me. I’ll ask him about it.
People reading this thread probably know this, but The Bridge of the Gods was named after a legend by the native peoples in that area. It told of a land bridge acrross the river that was there long ago. The arriving settlers thought that was all mumbo jumbo, but then geologists later established it as fact, due to the landslide. (Not that that helps with your enquiries, but I’ve always thought that was a neat bit of local history.)
And of course once the dam went in any vestige of a land bridge got covered by real deep water.
Bridge of the Gods is fun, it’s an erector set style bridge and the road bed is all that metal grill stuff with no asphalt on it. Whenever I take someone over it for the first time, I tell them to hang their heads out the passenger window and look down. That’s always good for a few gasps or choked screams depending on the acrophobia level of the passenger. That’s a stone deal for the dollar toll!
Ride a motorcycle over it! Quite the view. Plus, the grating tends to make your moto shift back and forth (like riding on grooved pavement when they are preparing to resurface). :eek:
It does that to cars too, but I’m sure that’s less alarming than a motorcycle. I crossed the bridge during an ice storm once and I think it took about three-four hours for my anal sphincter to unclench enough to pull the upholstery out of my ass. Do not recommend! Especially in a large van with huuuuuuge sail area.
Link went to a 3D view of the approach to the bridge that made it look like a flat bunch of metal draped down across several elevation changes, like it melted down a levee. Crazy looking.
