Watson's Grotto
Watson’s Grotto is the first room in the cave. The two entrances allow natural light in and create a “twilight zone” habitat, suitable for cave creatures such as spiders, crickets and bats. Rain and ground water mix with carbon dioxide (CO2) to form a weak acid known as carbonic acid. The carbonic acid from the surface eroded the top part of this room while stream water from the River Styx combined with the acid helped carve out the lower part of the passageway. Seen along the walls are cave formations known as cave popcorn, which formed due to the airflow.
Geology
Room Development
Passageways formed when water containing carbonic acid trickled down from the surface, enlarging joints and faults in the marble (Palmer 4; Klinchouk 667). These cracks started small but got larger and larger as the marble dissolved. The River Styx widened the lower sections, so the room is pear-shaped with a high narrow ceiling and rounded base (Veni 438; Roth 6).
The photograph on the left shows a smaller crack in the marble of Watson's Grotto in the red circle. The red lines highlight how these small cracks are made larger over many years.
In time, the cave eroded to form entrances. Oxygen-rich/carbon dioxide-poor air entered the cave and water drained out. Cave formations need room to grow and airflow to flush out carbon dioxide (Cigna 228-230; James 184).
Cave Formations
Numerous formations can be found throughout the cave. One of these is called cave popcorn, which can be found in Watson’s Grotto. Cave popcorn forms through a combination of evaporation and loss of carbon dioxide caused by seasonal airflow changes (Roth 8; James 183; Lundberg 320). The picture below shows water drops containing carbonic acid and dissolved calcite. When these drops of water are evaporated away by passing air, in this case from the entrance, cave popcorn is formed.
Water Flow
Water visibly flows through Watson’s Grotto. The River Styx is an underground stream, which is characteristic of karst topography. The water originates at the surface, percolates through the soil or sediments, and eventually ma
kes its way into the cave. Dye tests indicate that surface water takes between 24 to 52 hours to reach the cave (Barnes 4). The water generally moves through weaknesses in the rock—like joints and faults—and follows the easiest path. But some water moves very slowly through the rock itself (Palmer 88-91). In Watson’s Grotto, the River Styx erodes laterally. The lateral erosion is likely because the water flows on top of a layer of argillite, which is much harder to erode through than marble (Roth 6).
Barnes, Mary. Results of Dye-trace on South Fork of Panther Creek. Cave Junction: Oregon Caves National Monument, National Park Service, 1999. 1-5.
Cigna, Arrigo. “Climate of Caves.” Encyclopedia of Caves and Karst Science. John Gunn, ed. New York: Fitzroy Dearborn, 2004. 228-230.
James, Julia. “Carbon Dioxide-Enriched Air.” Encyclopedia of Caves and Karst Science. John Gunn, ed. New York: Fitzroy Dearborn, 2004. 183-184.
Klinchouk, Alexander. “Speleogenesis.” Encyclopedia of Caves and Karst Science. John Gunn, ed. New York: Fitzroy Dearborn, 2004. 666-668.
Lundberg, Joyce. “Karren.” Encyclopedia of Caves. David Culver and William White, ed. Burlington: Elsevier Academic Press, 2005. 315-321.
Palmer, Arthur N. Cave Geology. Dayton, OH: Cave, 2007. 4, 88-91.
Roth, John. “Interpretive Manual for the Monument’s Showcave”. Cave Junction: Oregon Caves National Monument, 2011. 6, 8.