Lost Lake, Oregon: The Lake That Drains Into a Hole Every Summer

eside one of the busiest highways across Oregon's Cascades, there's a lake that empties itself every year. Lost Lake sits just off Highway 20 near Santiam Pass, in the Willamette National Forest. In winter and spring it's a real lake, about 9 feet deep at its fullest, surrounded by pines and popular with anglers. But as summer arrives, the water level starts dropping. By late summer, in some years, the lake is mostly gone, replaced by a grassy meadow with a few pools. The water doesn't evaporate. It drains, down holes in the floor of the lake. The Forest Service describes two of them. One is about 7 to 8 feet across and about 6 feet deep, and when the water is flowing, you can hear it rushing into the ground. In 2015, a video of water swirling down the hole spread online and made the lake famous. The lake exists because of volcanoes. According to the Forest Service, it formed about 3,000 years ago, when lava from a nearby vent blocked an old river channel. The lava created a basin for water to collect, but it also left the ground below full of cracks and hollows. Several small streams flow into the lake, but the drain holes are its only known outlets. The cycle works like a sink with the drain left partly open. In fall and winter, rain and snowmelt pour into the lake faster than the holes can drain it, so it fills up. In summer, the streams slow down, the inflow drops below what the holes can carry away, and the lake empties. What's under the lake is still debated. The Forest Service has described the drain as a collapsed lava tube. A hydrologist who has studied it says it could be a lava tube or a sinkhole into a buried stream channel, and there's no way to know without a seismic survey. A Bend caver has argued that the lava flows in the area don't fit the pattern for lava tubes, and that the hole is more likely a collapse feature in the lava. In 2016, a new hole opened about 20 feet from the old one. Where the water ends up isn't certain either. It disappears into porous volcanic rock, and it likely recharges the underground aquifer that feeds springs in the area. Some believe it eventually reaches nearby Clear Lake, the source of the McKenzie River. Every fall the lake comes back, and every summer it goes down the drain again.