English: Western Kentucky's Mammoth Cave is the longest known cave on Earth, with 426 mapped miles as of March 2024. This moderately large block of limestone breakdown has anastomoses - networks of channels formed by dissolution of calcium carbonate at partings and bedding planes. Dissolution occurs as slightly acidic groundwater seeps or moves horizontally through the bedrock in the phreatic zone (at or below the water table). All groundwater is at least slightly acidic - the acid is usually carbonic acid (H2CO3) and some organic acids are also usually present. Carbonic acid forms by a simple chemical reaction: water + carbon dioxide = carbonic acid (H2O + CO2 --> H2CO3). This happens as raindrops fall through the atmosphere and also occurs as water percolates downward through soil and bedrock. The partial pressure of carbon dioxide gas is higher in soil gas, so even more carbonic acid forms in that environment. In landscapes with limestone bedrock, the slightly acidic groundwater dissolves the calcium carbonate (calcite) in the rock. This dissolutional action can result in caves and cave systems.

Once anastomoses are formed, beds below the parting plane or bedding plane are removed by gravitational collapse or complete dissolution. The result is a cave ceiling with a network of channels.

Locality: trailside breakdown block in Main Cave (between Mummy Ledge and Chief City), Mammoth Cave, Kentucky, USA

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(accessed with park permission)