The entrance to the Ape Caves on the south side of Mt. St. Helens is surrounded by bright green  moss and ferns and feels welcoming enough. But, within a few feet of the entrance, just beyond the stairs that lead into the lava tubes, the darkness consumes you. Without a light, you cannot see even a millimeter in front of your face.

For anyone with claustrophobia – and that would be me – entering the caves is a challenge. Fortunately, the lower Ape Cave tunnel, where we began our exploration, is big enough for visitors to be able stand and walk comfortably. These caves are the result of lava flows from about 2,000 years ago.

Basaltic lava flowed down the southern slopes of Mt. St. Helens toward the Lewis River. As the top of the lava flow began to cool, it formed tunnels, allowing molten lava to keep flowing underneath for months, perhaps even a year. Eventually, the molten lava flowed out of the tunnels and left these long lava tubes behind. The Ape Caves are nearly 2 1/2 miles long, the longest intact lava tubes in the continental United States!

Temperatures in the caves remain a steady 42-degrees year-round, so dressing warmly and carrying light are important for every visitor. The highlights of the lower cave are the railroad tracks – a section where there is a shoulder along the side of the lava flow – and the “meatball” – a  block of cooled lava that flowed on top of the hot lava and got wedged between two hard edges of the tube. The meatball hangs precariously above you as you walk through the cave.

After exploring the easier lower cave, we ventured into the more difficult upper cave and were confronted by huge piles of boulders (8 – 10 feet high) that we had to scramble over to proceed down the tube. After climbing over the first boulder pile, we knew this section would be more challenge than we were prepared for. It was really amazing, though, but way scary for me.

There are 27 boulder piles like that and an 8-foot tall lava wall to climb over to get to the end of the upper cave. At least at the end, you can climb out a ladder and hike the 1-1/2 miles back through the forest.

For anyone visiting the Mt. St. Helens National Monument area, I’d certainly recommend this as a stop. And don’t skip the Trail of Two Forests down the road – where you can crawl through a short lava tube left when lava cooled around downed tree trunks. Very cool!

To find out how the Ape Cave got its name, go here.