This trip to the Ape Caves took place in Aug. 1996).
We arrived at the caves around noon, quickly geared up, and began our hike. The walk from the parking lot to the cave entrance was only about 100 yards. The 'main' entrance is actually a sink hole that has been fitted with stairs, allowing easy access to the main cave 40 feet below. The cave itself is approx. 12,800 feet in length. It was formed about 1900 years ago when a lava flow from Mt. St. Helens filled an old river canyon with lava. As the exterior of this new lava bed cooled, the interior continued to flow, eventually forming a long, hollow tube. The information booth had a sign that said it took roughly 85 days for this to occur. Over the years, erosion has covered the upper layer of the tube making it virtually indistinguishable from the surrounding forest. The Ape Cave is currently the longest known lava tube in the Northern Hemisphere (or continental US depending on what literature you read!).
There are three 'entrances' to the cave, two of which have been modified for easy access (to which Tim Oerting can attest to - he tried the third to no avail). The 'main' entrance, which we used, enters the cave about a third of the way along its length. We went along the shorter (or lower) length first. This part of the cave was about 3/4 of a mile long and was very easy to traverse. The ground, although hard and somewhat irregular, was fairly level and posed no large obstacles. The cave ceiling varied in height from roughly 5 to 30 feet (much more than 15 feet on the average). We passed through several large 'rooms' where you could see where the lava had etched long, straight lines into the cave edges and dripping lava had cooled to forms 'frozen' drops on the ceiling. The vertical drop in the lower section was only about 150 feet.
The lower section ends gradually, beginning with a 5 foot high tunnel that eventually peters off to nothing. The literature that we picked up describing the cave indicated that back in the Early Kalama Period, about 450 years ago, an eruption caused a large amount of ash to be washed into the lower section of the cave, giving it it's smooth floor. Seasonal rains still cause the terminus of the lower cave to change on an annual basis. For more information on the Early Kalama Period (which occurred about 450 years ago), please E-Mail Alan deSalvatore at ADES@MICROSCAN.COM (he knows all about it).
After reaching the end of the lower section, we backtracked up to the main entrance where we entered the longer, upper section. This part of the cave was MUCH more difficult to traverse (and a lot more fun too)! There were many rock piles (where the roof had collapsed years ago?) that had to be traversed. These ranged between 5 and 25 feet in height. The ceiling height again varied from 5 to 30 feet but averaged less than in the lower cave. There were several sections where we had to climb up very steep grades (45 to 70 degrees) ranging in height from 3 to 25 feet. Midway through this section is a 90 degree, 10 foot vertical rise that you have to traverse using just foot and hand holds.
If you like caves, the upper section is a definite 'must do'. It took less than an hour to do the lower section (including the backtrack), but over two hours to the upper (one way). At the end of the upper section is another set of stairs that will take you to the surface. The terminus of the upper section is roughly 300 vertical feet above the main entrance (which means lava must flow downhill as Alan so deftly pointed out). The upper terminus is just that...a rock wall dead end. I suspect it is a 'plug' of lava that cooled more rapidly, hiding what may exist beyond.
After exiting the cave at the upper end, we rested and ate lunch. After 30 minutes or so we headed back down to the parking lot using an above ground trail (about 1 1/4 mile long). On the way down we saw 2 deer and several deer mice. Very cool! The entire hike took about 4.5 hours (parking lot to parking lot). I suspect that most able bodied adults and kids of 8 years or older could handle it. For any of you that are interested in doing this I would recommend bringing:
Primary light source per person (Coleman lantern or flashlight)
Secondary light source (in case of emergency - probably a flashlight)
Canteen (no water there)
Gloves (rocks are hard and sharp in many cases)
Fairly warm clothing...don't gear up for Winter...but maybe Fall??
After hitting the parking lot we took another 15 minute break, got in our cars, and then headed to "Lava Canyon" (a 15 minute drive from the Ape Cave...or 17 minutes if Bassam is driving). Lava Canyon provides an expansive view of the South East side of Mount St. Helens. You can see part of the blast zone and there is a reader board that provides information on the area. It's worth the drive on a nice day!