Oregon's Lost Lake

Every spring in Oregon’s Willamette National Forest, Lost Lake begins to drain down naturally occurring lava tubes. A six foot wide lava tube hole was featured in this 2015 video from The Bulletin, which notes, “The water is most likely seeping into the subsurface below and refilling the massive aquifer that feeds springs on both sides of the Cascades.” MentalFloss explains a bit more:

Lava tubes are a common feature of Oregon’s geology. They form after a volcanic eruption, when flowing lava cools and hardens near the surface while hotter lava continues to flow down below, carving a path as it goes. Occasionally, one of these tunnels will even break through to the surface, as in the case of Lost Lake.

Western Oregon’s rainy months—beginning in the fall—yield such a massive amount of precipitation that the basin fills in at a faster rate than the tube can drain it, and the lake reappears. It freezes over in the winter months, followed by a spring thaw that leads into summer when dry weather results in a (sometimes muddy) meadow. Then the cycle begins again.

Jude McHugh, a spokeswoman for the Willamette National Forest, says it’s hard to predict when the annual drain will occur. While the video makes it seem like a single, continuous flow akin to water in a bathtub, it’s actually a much more gradual process with ebbs and flows that vary from year to year.

Here’s another Lost Lake drain video from September 2010: