Mount Shasta is as beautiful and dramatic underground as above, hosting numerous natural caves and intricate lava tubes under its expansive environment, some of which can be explored today.
While caves can be created in a variety of ways, including rainwater, wind erosion, and sand erosion, for all their exoticism, they are formed from just two commonplace ingredients: rock and water. Not just any rock will do, however, as caves are generally formed from gypsum, limestone, dolomite, or salt.
Caves around Mount Shasta were formed when rainwater percolated through the soil, picking up carbon dioxide (from both the air and surrounding soil), to form a weak acid. This acidic water was squeezed between the cracks and layers of limestone, dissolving out a channel in the bedrock for the water to flow — a process that can take anywhere from around 50,000 years or so to millions of years.
More notable in this area are lava tubes, which are natural underground tunnels that are rapidly formed by the flow of fiery hot molten lava during volcanic eruptions.
When a volcano erupts, lava flows can create channels through which the molten rock passes. As the outer layer of the lava flow cools and solidifies, it forms a crust, insulating the still-flowing lava inside. This can lead to the development of a tunnel-like structure as the lava continues to flow and eventually drains out, leaving behind a hollow tube, not unlike a drinking straw.
These lava tubes can be enormous and run for miles in length, forming elaborate networks, stacked layer upon layer, throughout multiple eruptions, often occurring over many, many years.
Sometimes the roof of a hidden lava tube will collapse, exposing it to the surface. Sometimes the roof and/or floor of a lava tube will collapse, revealing the levels above or below. The fact of these collapses should serve as a warning to those who would explore the depths of Mount Shasta’s lava tubes, even as they beckon the way by providing a passage into the mountain’s mysterious netherworld.
Lava Tube Habitation
Lava tubes offer unique environments with relatively stable temperatures and protection from the elements, making them attractive habitats for various organisms, including humans. Lava tubes provide shelter for a variety of animals, including bats, insects, and other small creatures — as well as for deadly rattlesnakes seeking to escape the heat in the entranceways, and the occasional mountain lion lurking in the depths — as well as other living organisms that are adapted to the dark, humid, and cool conditions found deeper within the lava tubes.
While lava tubes are not as abundant around Mount Shasta as they are in some other volcanic areas, there are a few notable locations where they can be found. The most prominent of these is the fabulous Lava Beds National Monument. Located northeast of Mount Shasta, Lava Beds National Monument is known for its extensive system of lava tubes. This area was formed by the eruption of the Medicine Lake Volcano around 10,000 to 30,000 years ago and boasts more than 700 lava tube caves, with some being accessible to visitors. Notable lava tubes in this area include Mushpot Cave and Skull Cave.
In addition to its lava tubes, Mount Shasta Caverns, a popular tourist attraction that is easily accessible south of the mountain along the shores of Shasta Lake, offers visitors a tour of limestone caves that have formed in the marble rock near Mount Shasta. These more traditional caves were not created by volcanic activity, but by the dissolution of limestone rock over countless years, creating the beautiful formations underground.
While less commonly explored, there are also reports of small caves and lava tube-like structures on the slopes of Mount Shasta itself. These features are not as extensively studied or accessible as the ones at Lava Beds National Monument, however.
It is important to note that while caves, mines, and lava tubes can provide interesting opportunities for exploration and scientific study, they should be entered with caution and proper equipment, as they can pose many risks due to uneven terrain, potential collapses, the darkness of the environment, and more.
In summary, lava tubes are formed by the flow of molten lava during volcanic eruptions, creating underground tunnels. While there are not as many lava tubes directly under Mount Shasta, the nearby Lava Beds National Monument is known for its very extensive system of lava tubes. These underground environments offer unique habitats for various life forms and provide opportunities for exploration and scientific study for those who are properly equipped and prepared.