Spiral Stairs
The circular area encompassing the spiral staircase was dissolved by flowing water. This created a shaft called a domepit. The water was funneled through joints and faults over a layer of water-resistant, impermeable argillite and slowly dissolved the marble. As the water receded, drapery, flowstone, and cave bacon formed around the edges.
Geology
Room Development
The Spiral Staircase stands in a domepit or a rounded vertical passageway. Domepits often show rillenkarren on the walls and are usually created by showering water (Bates and Jackson 194). The name domepit is an informal term that cave explorers came up with. Looking up, the shaft looks like a dome and, looking down, the shaft looks like a pit (Palmer 139).
Water drilled through the marble, dissolving calcite. This water is more aggressive (acidic) because it flows over argillite. Argillite is impermeable, meaning water cannot readily pass through it. Since the argillite stops the water from coming in contact with marble, calcite is not dissolved as the water travels along the argillite and it stays more acidic. At the Spiral Stairs, the argillite has eroded away, and this aggressive water enters the cave system (Hess 445; Palmer 140; Roth 254). Other domepits are found at Miller’s Chapel and Paradise Lost.
Cave Formations
As cave entrances formed, carbon dioxide was able to leave the cave, the water became less acidic, and formations started to grow. Also, as the water flow decreased, the water became more saturated in calcite.
Drapery and flowstone can be seen at the top of the room, as well as cave bacon. Soda straws, stalactites, flowstone can also be seen on the left side of the room.
Water Flow
Another water collection bucket can be seen on the way to the Spiral Stairs from Niagara Falls. This bucket, like the one seen on the floor of the Imagination Room, helps resource staff monitor how much and how long it takes for water to enter the cave (McCall 1; Roth 30).
Bates, Robert and Julia Jackson, ed. Glossary of Geology. Alexandria: American Geological Institute, 1987. 194.
Hess, John. “Pits and Shafts.” Encyclopedia of Caves. David Culver and William White, ed. Burlington: Elsevier Academic Press, 2005. 444-447.
McCall, William. “Infiltration and Fire Suppression: Preliminary analysis of tipping bucket data to determine whether fire management activities have a measurable effect on infiltration into the cave.” Cave Junction: Oregon Caves National Monument, National Park Service, 2008. 1-9.
Palmer, Arthur. “Influence of geology on cave patterns.” Cave Geology. Dayton: Cave Books, 2007. 138-140.
Roth, John. “Interpretive Manual for the Monument’s Showcave”. Cave Junction: Oregon Caves National Monument, 2011. 254.
Veni, George. “Passages.” Encyclopedia of Caves. David Culver and William White, ed. Burlington: Elsevier Academic Press, 2005. 436-440.