Ape Cave Lava Tube
Mount St. Helens National Volcanic Monument, Washington
Ape Cave Lava Tube in Mount St. Helens National Volcanic Monument, Washington is a lava tube system featuring 2.5 miles of surveyed passages and a vertical relief of 80 ft. Rated under crawlways & squeezes accessibility, exploring this cavern requires adherence to White-Nose Syndrome bat decontamination protocols, sturdy footwear, and three independent light sources.
Speleological Profile
Unlike solution caves dissolved over millions of years by acidic water, Ape Cave is a volcanic conduit formed when fluid basaltic lava (approx 2,000°F) crusting over at the surface while molten lava drained underneath. The cave is divided into two distinct experiences: the Lower Cave (0.75 miles one way) is a relatively smooth, flat walk down a subterranean basalt subway tunnel. The Upper Cave (1.5 miles) is an athletic obstacle course requiring scrambling over giant rock piles, scaling an 8-foot sheer lava wall, and exiting through an open volcanic skylight ladder onto the forest floor above.
Famous Chambers & Features
- Longest continuous lava tube in the contiguous US (13,042 ft)
- Upper Cave 8-foot lava fall boulder scramble
- Lava stalactites (lavacicles) and flow ledges
- Total pitch darkness with no artificial trail lights
Required Speleology & Exploration Gear
Leave No Trace Underground & Cave Conservation
- •Never touch cave slime (biofilm/actinobacteria) on basalt walls; this fragile microscopic ecosystem feeds subterranean invertebrates.
- •Strictly pack out all trash, food scraps, and used batteries.
- •Stay off fragile sand banks formed by ancient glacial floods.
Visitor Information
US Forest Service timed reservation ticket required May through October via Recreation.gov.
Mandatory boot bio-sanitization before entry and upon exit.