Exploring Washington’s mysterious disappearing lake | Oregon Field Guide

This is one of my favorite places on the forest and I've felt that way for a long time. Okay let's turn to your left. And I come here every year so it's not that it's new. It appeals to all of my aesthetic senses. The first thing we noticed when we set out with Andrea Ruckte and Justin Ewer on this lake was its strange bayou-like feel. Do you see the aspens to the left? Look through those cottonwoods there. Can you see that? Where else in the northwest can you paddle through groves of cottonwood, aspen, and lodgepole pines and not be along a flooded river? I honestly have never heard of another habitat that is like this one. Look at that beautiful cottonwood snag. You know when they get so old they get really complex with their branching systems and there will be tops that have died and so you can have some cavity excavators that create you know holes up there so you know it's just very rich habitat. We're in a place called South Prairie in the Gifford Pinchot National Forest of southwest Washington. Andrea is a botanist here. She says there are a lot of lakes in the area but this one is unique because it disappears every summer. When we come back here in a few months this will be a beautiful little grassy glade and it will be a beautiful place to come with a picnic. By July, the 85-acre lake is gone, replaced by a prairie. No springs, no wetlands, no water anywhere. You'd never know it was a lake other than you come out here in the summer and you wonder why is there driftwood at the edge of this meadow? When we set out to learn what's going on here we heard that there hasn't been much research into this phenomenon but Andrea says we can rule out natural springs as a cause as well as river flooding since there's no river nearby. So what gives? We can hear it and I'm kind of trying to see if we can see some flow but it's right in here. Andrea finds a clue in a small seasonal creek that runs into the lake. All right here's the creek that's feeding the lake that becomes a dry meadow. That alone shouldn't do it. Lots of forests have creeks running through them but then Andrea paddles to the other end of the lake. It's here that water butts up against a 20 square mile landscape called the big lava bed. I mean I really do think of it almost like a bathtub and we don't exactly understand why it acts like a bathtub. You know the theory being is that it's backing up against this big lava flow. Andrea thinks something is happening inside this 9,000 year old lava flow. It is very likely that there are lava tubes below us that are frozen. She says frozen ice could be acting like a dam. But we don't understand exactly why and where the drainage occurs but we just knew it happens really quickly. This seems like one of the places where the stopper goes into the bathtub. This was a hard theory to test while the lake was still up to eight feet deep. So we returned in July to find some answers. Oh yeah right here. Yeah so right here's the the pollen line where the pollen was floating on the water and kind of stuck to the tree. As we made our way to the lava flow we passed through a meadow that's as rare as the lake itself. Most meadows on the west side are meadows because they're wet meadows but this place is actually dry right now. It's it's very dry. You can see like how dry it is. Uncommon environments often give rise to uncommon species. Here at South Prairie you can find the world's largest known population of this tiny blue flower. Here it is. This is Syrenchium Sarmentosum is our rare iris and it was actually found here in 1893 and this was the first site for it and it really likes it here. It's perfect for it here. Among trees there's an oddity here as well. You don't find many aspen this far west in the entire state of Washington. They are a species that just needs light. They can't compete with conifers. So they're a little bit like our rare iris in that they're here at South Prairie probably because the inundation has kept the habitat open so they can get that light. But we were on a quest to find that drain plug that causes the lake to appear and disappear each year. Andrea figured it would be somewhere in the lava flow at the edge of the meadow. After a few hours of hiking she found a cave that she'd never noticed before. So you can really see that if there was an ice dam and it was ice up in there how the water would rise up and form this lake and we paddled right through this area when it was full we couldn't see this cave. The lava waterway. Yeah this is exactly the kind of place that I think could easily function as a drain because it looks like this cave kind of keeps going back. So it's it's a theory but it's a very credible theory and it would explain why South Prairie drains relatively quickly. Fills with water is a lake and then drains within about three weeks. To be clear Andrea is a botanist not a hydrologist but like us she just happens to love a good mystery. What we know is that when springtime comes the open meadow will fill up again and become the closest thing to a southern bayou you can find in the northwest. To me this is one of the most peaceful places that you can come. It's a good place to paddle and ponder a small wonder in our own backyard. You come out here and you kind of just go wow it strikes something in you and I don't know it's aesthetic it's intangible. I think that it would be a great thing if we could find out more about what makes this place what it is. Getting inspiration for your next adventure it's kind of why you're here right? Well you can support more of what we do at Oregon Field Guide and everything else you see on OPV by going to opv.org slash video and becoming a sustaining member.