CAVES AND KARST PROCESSES, GRAND CANYON, ARIZONA, USA

Grand Canyon caves fall into two main categories: those formed under unconfined conditions and those formed under confined conditions. Unconfined caves are simple underground conduits through the vadose zone, fed by infiltration into the Kaibab Plateau, through which water moves by gravity along faults or master joints as free-surface streams. These caves usually discharge into the canyon from the base of the Muav Limestone and above the Bright Angel aquiclude. Confined caves are those that formerly developed (or are developing) in the phreatic zone under confined condtions. Grand Canyon confined caves are hypogenic; that is, they owe their origin to solutional aggressiveness generated at or below the water table where dissolution is due to the mixing of hypogenic H₂S-CO₂-bearing waters with epigenic meteoric waters. Only confined caves contain mammillary and folia speleothems and replacement gypsum that can be dated and related to the general lowering of the water table and incision of the canyon over time.

Karst piracy is a type of stream piracy where a subterranean drainage connection is made under a topographic divide. The terms "piping" and "groundwater sapping" should not be used for karst piracy. Karst piracy has been proposed as the process by which the eastern and western sides of the Kaibab arch were connected at ~6 Ma via caves in the Redwall Limestone. Only the Kaibab arch section of the canyon has this proposed origin, not the entire Grand Canyon. The caves along the Grand Wash fault in the western Grand Canyon are hypogenic confined caves. They did not form by the process of infiltration-dissipation from the Colorado Plateau to the Grand Wash trough. C-O isotopic and DZ data favor karst piracy rather than lake spillover and a time of connection under the Kaibab arch at ~6 Ma. Karst piracy is a well-established mechanism of drainage integration around the world. Notable examples include sections of the Danube River, Swabian Alb, Germany and Yangtze River, Three Gorges region, China