File:Flowstone (Butterscotch Falls, Mammoth Dome, Mammoth Cave, Kentucky, USA) 1 (46459767855).jpg

Travertine flowstone in Mammoth Cave, Kentucky, USA.

Western Kentucky's Mammoth Cave is the longest cave system on Earth, with 412 miles known and mapped as of fall 2017. The name does not refer to the early discovery of fossil mastodon or mammoth bones here. Rather, the name refers to the immense size of many rooms and passages.

The system has a variety of cave passages: tubular passages, canyon passages, vertical shafts (domepits), keyhole passages, and giant canyon passages.

The flowstone structure seen here is in Mammoth Dome, a large, complexly-shaped domepit that can be viewed during the 2 hour, 2 mile long Historic Tour. Domepits are large, silo-shaped, dissolutional features in caves. They form in the vadose zone (above the water table) as downward-moving groundwater dissolves limestone. Mammoth Dome corresponds to a surface sinkhole (Mammoth Dome Sink) that can be observed along a hiking trail that originates near the park's visitor center.

One measurement puts Mammoth Dome at 150 feet tall. Park signage asserts that it is 192 feet tall.

The rocks in Mammoth Dome include the Ste. Genevieve Limestone and the St. Louis Limestone (both Middle Mississippian).

Mammoth Dome is one of the few areas along the Historic Tour to have "cave formations", which are properly called "speleothem". All secondary mineral deposits in caves are known as speleothem. Most cave formations are composed of calcium carbonate (CaCO3 - usually in the form of calcite, but sometimes aragonite). Calcareous speleothem is referred to using the rock name "travertine", a crystalline-textured, chemical sedimentary rock formed by precipitation from water.

Dripstone and flowstone are the most common forms of travertine speleothem. Dripstone forms by calcium carbonate precipitation from dripping water. Flowstone forms by calcium carbonate precipitation from thin sheets of flowing water. The most common forms of dripstone are stalactites (attached to ceilings), stalagmites (growing from the floor), columns (= fused stalactite-stalagmite pairs), and draperies (= curtain-like sheets formed as water drops descend along an inclined surface). Flowstone often has the appearance of frozen waterfalls.

Seen here is a yellowish-brown colored flowstone mass in Mammoth Dome called "Butterscotch Falls". This site was visited one day after a rain event, so actively-flowing films of water were present on the flowstone.