Ape cave National Volcanic Monument

Ape cave National Volcanic Monument in Washington

Mount St. Helens Ape Cave Lava Tube is a popular attraction in the Mount St. Helens National Monument and the longest lava tube in the continental United States at over two miles in length.  The Ape Caves are located on the south side of Mount St. Helen's and accessed through Woodland - go up highway 503 past Cougar. 

How the Ape Caves were formed:  About 2,000 years ago lava poured down the southern flank of Mount St. Helens in streams.  As the lava flowed the outer edges of the lava stream cooled forming a hardened crust which insulated the molten lava beneath.  This allowed the lava to remain hot and fluid encased in this “lava tube” and continued flowing months during the eruption.  The end result was the creation of this spectacular 13,042 long lava tube.  This formation is especially unusual at Mount St. Helens as this type of volcano usually erupts lava of a much thicker consistency which tends to block flow and build up pressure resulting in explosive eruptions like the blast of 1980. 

Ape Cave Information

·         The Third Longest lava tube (13,042’ long) in North America

·         Be sure to practice “Leave No Trace” ethics

·         Cave temperature is 42°F/5.6°C year-round

·         No pets, food or drink allowed inside the cave, except water.

·         Hike to the lower tube is easy (and the upper is more difficult)

·         Click here for more on information on Ape Cave Lava Tube Hike

·         Complete darkness
·         Dripping Water and blowing breezes

Hiking the Ape Caves:   The lower Ape Cave is approximately is .75 miles long and can be hiked down and back in an hour.  It is most famous for “Meatball” - a block of cooled lava which fell from the lava tube ceiling while lava was still flowing through the cave.   Floating on the surface of the lava flow it was carried downstream until it became wedged in a narrow spot above the present cave floor.  This large lava tube is very interesting and not too difficult a walk in the lower tube (just watch your step.)

How to Reach: Driving time from I-5 and highway 503 where all the Mount St. Helens Visitor Centers are to the Ape Cave is just over an hour.   The Ape Caves are open year-round though the parking lot gets snowed in during the winter.

From I-5 exit 21, travel north and east on State Route 503 (Lewis River Road). At 23 miles from the freeway, continue straight on Spur 503. At 31 miles, Spur 503 becomes Forest Road 90. Cross a bridge over a canal, then 2.6 miles later, turn left on FR 83.