This EarthCache takes you into the heart of a volcanic landscape dominated by Pisgah Crater, a basaltic cinder cone in the Lavic Lake volcanic field. The surrounding lava flows contain lava tubes—natural underground passageways formed by flowing lava that provide an exceptional opportunity to observe volcanic processes up close.
Lava tubes are a remarkable record of volcanic processes — they preserve how molten lava flowed, crusted over, and drained away, leaving behind hollow tunnels. At Pisgah, these features are among the best regional examples of lava tube development in a young volcanic field.
Formation of the Pisgah Crater Lava Tubes
1. Basaltic eruption and lava flow
Pisgah Crater erupted basaltic magma that was extremely hot and low in silica, allowing the lava to flow easily across the desert surface. This fluid behavior enabled the lava to spread in broad sheets rather than piling up near the vent. As the lava moved away from the crater, it maintained enough heat and mobility to travel long distances, which is a critical requirement for lava tube development.
2. Cooling of the surface and formation of a solid crust
As the lava flowed outward, the surface was exposed to cooler air and rapidly began to solidify. This cooling created a hardened basalt crust on top of the still-molten interior. The crust thickened over time and acted as an insulating layer, slowing heat loss and allowing the lava beneath to remain liquid even after the surface appeared solid.
3. Insulated flow beneath the crust
Once the crust became strong enough to support its own weight, lava continued to move underneath it in a confined channel. This insulated pathway reduced friction and heat loss, allowing lava to flow efficiently beneath the surface. At this stage, the lava tube functioned as a natural pipeline, transporting molten lava away from Pisgah Crater.
3.5. Establishment of a stable lava tube
Continued flow beneath the crust widened and smoothed the interior of the tube. The constant movement of lava polished the walls and ceiling, leaving behind flow lines and ropey textures that can still be seen today. These features record the direction and depth of lava movement within the tube.
4. Drainage of lava as the eruption ended
As volcanic activity declined, the supply of lava feeding the tube decreased. Gravity caused the remaining molten lava to drain downhill and exit the tube system. This process left behind an empty conduit, preserving the tunnel shape and internal textures created during active flow. After the tube emptied, the remaining heat slowly dissipated and the basalt fully solidified. Cooling caused contraction, which sometimes produced cracks or weakened zones in the ceiling and walls. Drips of molten lava from the ceiling may have formed small lava stalactites, known as lavacicles.
5. Collapse and formation of skylights
Over time, sections of the lava tube roof weakened and collapsed due to gravity, weathering, and minor seismic activity. These collapses created skylights and entrances that expose the interior of the tube. The angular blocks surrounding these openings are evidence of roof failure rather than erosion by water.
Works Cited
https://en.wikipedia.org/wiki/Pisgah_Crater
https://discovernewberrysprings.com/pisgah-crater
https://digital-desert.com/pisgah-crater/index.html
https://www.nps.gov/subjects/volcanoes/basaltic-lava-flows.htm
https://caves.org/lava-tubes/
https://home.nps.gov/media/photo/view.htm?id=2EF1195A-A050-49F4-9FA9-DBE561B366DE
TO LOG A FIND ON THIS CACHE YOU MUST ANSWER ALL THE QUESTIONS BELOW. YOU CAN CONTACT ME THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER TO SEND YOUR ANSWERS. ANY INCORRECT ANSWERS MAY RESULT IN A CLARIFICATION RESPONSE FROM ME.
1. "Pisgah Crater - Lava Tubes" on the first line of your email AND list all geocaching names of your party so I can match your answers to them. If you all want to learn something, I would prefer each cacher send me individual emails in the spirt of earthcaching.
2. Take a photo of you (or your signature item if you don't want to show your face) inside the lava tube. This photo MUST be attached to your "found it" log.
4. As you enter the lava tube, describe the texture of the rocks as you go deeper underground. How do they compare to the surface exposed rocks at the tube's entrance?
4. What process might cause the texture of the rocks to be the same (or different)?
5. Once inside the flat part of the tube, where you can easily stand and walk around, estimate the size (or diameter) of the tube.
6. As you walk deeper into the tube, look for evidence of flow direction. Was the lava flowing towards the tube's entrance or away from it? Support your claim using the evidence you see. Hint: look for cooled lava plumes along your feet that show the flow direction or high level lines similar to floods that are marked by ledges or shelfs. Additionally, you may infer the flow direction based on the elevation gain/loss as you walk deeper in the tube.