Taking a Geological Tour of the Ape Cave With the Mount St. Helens Institute


    Located on the south side of Mount St. Helens, the 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 more than two miles in length.

    The cave is open for self-guided exploration year-round (although the site is often inaccessible due to heavy snows in winter). Ranger guided tours are available June through early September.

    Last Saturday, I took the opportunity to take a tour through the Ape Cave and over the surrounding trails in a geological field seminar sponsored by the Mount St. Helens Institute and led by Dr. Charlene Montierth, head of the Clark College geology department.

    “Taking a guided, focused tour adds another level to your hike and your enjoyment of the outdoors,” said Ray Yurkewycz, science education coordinator for the Mount St. Helens Institute, who also accompanied the group hike.

    The two mountain steward volunteers who accompanied us on our hike — Chris Stanton, a middle school math and science teacher, and Pam Stewart, a geophysics student at the University of Oregon — added another level of information.

    Field seminars are generally limited to 10 participants, which allows plenty of time for questions and answers for each individual.

    The day began with a short walk through the cool forest, past the Ape Cave main entrance and out into an open field where the classroom gathered found seats on a tumulus mound of broken up lava, created as the surface of the lava cooled and created a crust and then was pushed up and broken apart as the active lava flowed beneath the crust.

    “This lava flow that we’re sitting on is about 2,000 years old,” Dr. Montierth told the class.

    The view of Mount St. Helens from the Ape Caves isn’t the most stunning view. That is until your realize that in its explosive past, the far away mountain in the distance had a far reach that could affect the land even farther than where we were sitting.

How the Ape Caves Were Formed

    About 2,000 years ago lava poured down Mount St. Helens’ southern flank in streams. As the lava flowed, the edges of the lava stream cooled. The cooling lava stream formed a hardened crust, which insulated the molten lava below and allowed the lava to remain hot and fluid, encased in a “lava tube.”

    After the molten lava on the inside drained away, the hardened outer crust was in place, forming the cave. Lava stalactites and stalagmites and flow marks can be seen on the walls and floor of the cave.

    The lower Ape Cave is about is .75 miles long and can be hiked down and back in an hour. The cave dead-ends at a narrow tunnel that continues on for a long way, while crawling on hands and knees along the sandy surface.

    The lower cave is most famous for “Meatball.” The meatball is a block of cooled lava which fell from the lava tube ceiling while lava was still flowing through the cave. The meatball floated on the surface of the lava flow it was carried downstream until it became wedged in a narrow spot above the cave floor.

    The upper Ape Cave is 1.5 miles long and takes about 2.5 hours to complete, returning on a surface trail. There are 27 boulder piles and an 8-foot-high lava fall for the more adventurous cavers to climb to get through the upper end of the cave. The cave ends at a long metal ladder to the surface.

How the Ape Caves Were Named

    “It just blows my mind how the cave was named,” said Dr. Montierth. “It was discovered by a logger — and loggers are sometimes known as mountain apes.”

    Logger Lawrence Johnson in 1947 almost drove his tractor into the main entrance. Johnson told his friend Harry Reese about his discovery. Reese then led a Scout troop into the cave to explore and map the cave — they were known as the Mount St. Helens Apes Boy Scout troop.


    Kimberly Mason is a freelance writer based in Cinebar. She can be contacted at kz@tds.net.