A placid mountain lake in central Oregon lives up to its name, Lost Lake, by disappearing every spring. This year, video capturing the annual phenomenon has gone viral.

As the above video shows, Lost Lake drains rapidly through a six-foot (two-meter) wide hole in the lake's bottom, morphing into a quiet meadow in late spring. Early in the following spring, the lake fills up again, as snowmelt from the surrounding Cascade mountains accumulates faster than water can drain out through the hole.

That hole is really a lava tube—a geologic feature made when lava cools around the edges of a river of molten rock. After the hot lava drains away, it can leave an empty space. There are many such tubes