Buffalo National River's geology: 500 caves under the Ozarks

Buffalo National River, in the Ozark Mountains of northern Arkansas, was the country's first national river: 135 miles of free-flowing water between sandstone bluffs, with more than 500 caves along it. Few places in the National Park System have as much karst — the landscape of sinkholes, sinking streams, springs and caves that forms when water dissolves rock.

The river in brief

How the karst formed

The bedrock is Paleozoic sedimentary rock laid down from the Ordovician to the Pennsylvanian period, in the Ozark Plateaus physiographic province. Two things together made the caves and sinkholes:

1. Soluble rock. A thick sequence of Ordovician carbonates — the Fernvale and Kimmswick Limestones, the Powell and Cotter Dolomites and the Plattin Limestone — dissolves in slightly acidic groundwater.
2. Broken rock. Faults, grabens, folds and domes fractured the bedrock, and the cracks gave water paths to follow. Water dissolving outward from those paths, above and below ground, opened the caves, swallowed the streams and left the sinkholes.

Above, the river has cut slowly down through the layers, leaving sheer sandstone bluffs and waterfalls. The youngest deposits are Quaternary: river terraces, channel gravels and slope debris along the Buffalo and its tributaries.

The Park Service's Geologic Resources Inventory has published geologic maps and a report for the river, and its Soil Resources Inventory has completed a soil survey; all are free on the NPS DataStore.

Sources

Written from "NPS Geodiversity Atlas—Buffalo National River, Arkansas", National Park Service Geologic Resources Division, a work of the United States government in the public domain, which cites Haley et al. (1993).