Geology…
(Reprinted from “Caves of Mount St. Helens – Guidebook”)
Mount St. Helens National Volcanic Monument contains one of the largest concentrations of caves in the Northwest. The geology and caves found here are unique in their variety of sensitive resources, and young age. Unfortunately, unlike limestone caves, the appreciation of lava caves hinges upon a heightened awareness of volcanology through education. Lava tubes are generally not an “ohhh, ahhh” type of experience.
to the Cave Basalt Flow. This entered several caves, depositing sand and gravel on the floors. Hopeless Cave, a small lava tube up slope from the main entrance to Ape cave, was completely filled. As you walk Ape Cave Trail you cross one of these alluvial flows.
THE WIND DOES BLOW!
When more than one entrance exists, significant air movement may takes place. Cave wind is caused by differences in air temperature inside and outside the cave. During the winter, warm cave air rises like smoke in a chimney, and pours from upper entrances. This chimney effect reverses itself during the summer when cool cave air drains down- slope and rushes out through lower openings or cracks. Cave wind in Ape Cave has been measured at seven (7) miles per hour.
LAVA KARST!
At Mount St. Helens, a watershed of approximately 17 square miles drains entirely beneath the Cave Basalt Flow. All precipitation falling in the watershed disappear into the lava, either directly or as sinking streams. Two large springs, one at Dry Creek, and the other at Cougar Creek are resurgences. Water has been dye traced from upper Cougar Creek at Grass Lake three miles underground to Cougar Creek Spring, in a little less than three days. This rapid ground water transit can only be accounted for by open channels beneath the lava.
In Little Red River Cave, Lake Cave, and Ape Cave, water channels have developed along the contact between the overlying lava and buried paleo soils. Water collecting beneath the lava enters the caves at points where wall linings have collapsed exposing the buried soils. These erosion channels are as much as several hundred feet long. Over the last few years, similar erosional caves have been found along the margins of the Cave Basalt Flow. Some carry water all year and are still being surveyed. The “master” channels which carry most of the water flow to the large springs have not been entered. but are expected to be similar to those already found.
Two caves, Little Red River and Lake Cave, contain seasonal streams and lakes at their terminus. Lake Cave only has water during the winter months, but Little Red River Cave has perennial flow, and a semi-permanent lake. The unusual name of this last cave comes from iron oxide stains found in the stream bed.
CAVE SOFTLY!
Caves at Mount St. Helens contain a variety of sensitive resources. These include rare or endangered plants and animals, geologic features, formations, unusual hydrology, deposits of bones, and unique strains of microorganisms that have been undisturbed for thousands of years.
The ultimate goal while visiting a cave is to avoid having a negative impact on cave resources. Many cave formations are extremely fragile. To prevent damage, stay on well worn or marked trails. If Sand Castles (drip eroded deposits of volcanic sand) or clay covered floors are encountered, avoid walking across them. Your footprints may destroy thousands of years of natural sculpting and development.
Lava stalagmites and bead-like globules of lava drip are found on the floor in some caves. These are fragile and will be crushed if stepped on. Avoid these areas or stay on established trails. At no time is it justifiable to break formations or cause damage for the sake of exploration. Responsible cavers always back away from entering areas where their presence could cause damage.
Many lava tubes have tree roots hanging from the ceiling where they enter through cracks. These are a primary source of food for cave invertebrates, rare cave adapted insects that must survive in a food-poor environment. Avoid contact with roots or disturbance to any other organic material found in caves. Even removal of human transported wood from caves should only be done after examination by a cave biologist to make certain that cave insects are not using it as a food source.
Aquatic invertebrates living in pools or cave streams are particularly vulnerable. Avoid unnecessary wading or walking in permanent water bodies. Never wash your hand or rinse mud off boots or clothing in cave pools or streams.