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

By Kimberly Mason / For The Chronicle
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.
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Kimberly Mason is a freelance writer based in Cinebar. She can be contacted at kz@tds.net.
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Upcoming Field Seminars
Aug. 6: Geology in the Heart of the Blast Zone
Aug. 13 (Hiking Day): Discover the Secrets of the Harmony Trail (Aug. 12 Optional Evening Campout)
Aug. 13 (Climbing Day): Geology on High: A Summit Climb of Mount St. Helens Aug. 12 (Optional Evening Campout)
Aug. 19: Plants of Recovery Backpacking Adventure
Aug. 27: History Unveiled: Geology of Lava Canyon
Sept. 10 (Hiking Day): Into the Mouth of Destruction: Geology of the Pumice Plain (Sept. 9 Optional Evening Campout)
Sept. 17 (Hiking Day): Into the Crater: A Guided Science Hike to Crater Glacier (Sept. 16 Evening Campout)
Oct. 8: Ape Canyon: Lahars, Big Trees and Fall Color
Oct. 22: Foraging for Edible Mushrooms

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If You Go:
The Ape Cave is located on the southern side of Mount St. Helens. There are two ways to go. You can take Interstate 5 south to Woodland, take exit 21 and follow the signs to the Ape Cave or take U.S. Highway 12 east into Randle and follow Forest Road 25 south, then Forest Road 90 west, then follow the signs.
A $5 National Forest Day Pass or $30 Annual Northwest Forest Pass is required. The day pass is available for purchase at the ranger station.
Arrive early, the parking lots for the Ape Caves are typically filled by noon on weekends.
The Ape Cave stays a consistent 42 degrees, even in the heat of the summer. Bring warm clothing to layer on as you descend into the mouth of the cave.
Wear sturdy-soled shoes, preferably hiking boots. The floor of the cave is a rocky and uneven surface most of the way.
Carry a lantern and wear a headlamp. The cave is very dark, your feet will be plunged into darkness just steps away from any light source and the uneven, rocky terrain is very hard to navigate without a light source. Lanterns are available for rent at the ranger station located at the head of the Ape Cave trail from June through early September.
A word of caution to parents:
While the Ape Cave is a popular destination for families and a relatively easy hike for youngsters, it is also a very dark and cold environment. If you walk to the end of the lower cave passage, it will be like spending an hour standing in your refrigerator. The swinging lights and lanterns in the dark cave create a shadowy presence that may intimidate many young children.

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About the Mount St. Helens Institute
Founded in 1996, the Mount St. Helens Institute is a nonprofit organization devoted to helping people understand and protect the volcano. The institute sponsors field seminars, guided climbs, lecture series, work parties, and other outings. They are supported by generous businesses and individuals from across the country and seek to share their enthusiasm for the Pacific Northwest’s youngest and most active volcano.
Visit the Mount St. Helens Institute on the Internet at http://mshinstitute
.org or call (360) 449-7883 for more information.

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