How Caves Formby Jonathan DuHamel on Mar. 15, 2010, under Geology
How many caves are there in Arizona? By one count, more than 1,600. Most of us have been to Colossal Cave in Tucson, or Kartchner Cave near Benson. Both of these are limestone caves. In northern Arizona, some caves are formed by lava tubes.
Limestone caves have a geologically short lifetime, usually less than a few million years, and more often, just a few thousand years.
Most limestone in Arizona was deposited when the area was beneath the sea during the Paleozoic era 500 million to 250 million years ago. Both Colossal Cave and Kartchner Caverns occur within the approximately 330-million-year-old Escabrosa Limestone.
Limestone caves are solution caves that form just below the water table. Groundwater, made slightly acidic by dissolved carbon dioxide, passes through cracks and pores, and dissolves some of the limestone. In some areas, such as at Colossal Cave, weak sulfuric acid from volcanic exhalations, also helped dissolve the limestone. Over time, the cavities become larger, and, if the water table is lowered due to erosion outside the cave, multilevel passages are formed.
Cave decorations such as stalagmites stalactites don’t form until the cave is exposed to the air, perhaps by a stream intersecting one of the passages. Once that happens, cave formation ceases. It’s just like opening a can of soda pop; the carbon dioxide dissipates leaving the water less acidic. The calcium carbonate in the water is deposited as the water evaporates.
The final stage in the life of a limestone cave is collapse. As the water table lowers and surface erosion continues, the caves dry out and the ceiling of caves collapse, producing sink holes. The end stage is a land-form called Karst topography characterized by subterranean drainage which leaves a barren surface, and after more erosion, can leave limestone spires.
Lava tube caves occur in the San Francisco volcanic field near Flagstaff. These were formed about 700,000 years ago within lava flows when a crust is formed around a flow channel and the still hot fluid lava flowed out of the cylindrical crust. Lava tube caves can contain formations similar to limestone caves if conditions are right. The longest known lava tube cave is Kazumura Cave in the eastern slope of Kilauea on Hawaii. It is 3,614 feet long.
Caves can form in other kinds of rock. The voids are usually produced by faulting or erosion, especially along a seashore. Caves also form in ice.
The cave system with the greatest total length of surveyed passage is Mammoth Cave, Kentucky, with 367 miles of passages.
The longest surveyed underwater cave is the Ox Bel Ha Cave System in Yucatán, Mexico with 110 miles of passages.
The deepest known cave (measured from its highest entrance to its lowest point) is Voronya Cave (Abkhazia, Georgia), which is 7,190 feet deep.
The deepest vertical shaft in a cave is 1,980 feet in the Vrtoglavica Cave in Slovenia.
The largest room ever discovered is the Sarawak chamber, in the Gunung Mulu National Park (Miri, Sarawak, Borneo, Malaysia), a sloping, boulder strewn chamber with an area of approximately 2,300 feet by 1,300 feet and 260 feet high.
For a story on how caves contribute to our knowledge of sea level fluctuations, see:
For more on the geology of Arizona, see my seven part series beginning here.