FORMATION AND CLASSIFICATION OF NATURAL ARCHES IN THE RED RIVER GORGE GEOLOGICAL AREA, EAST-CENTRAL KENTUCKY - PRELIMINARY INVESTIGATIONS
The Natural Arch and Bridge Society has created a classification scheme based on observable attributes such as context (surroundings in which the arch occurs), morphology (shape of various parts of the arch), metrics (size of various parts of an arch), geology (type of rock or formation in which the arch occurs), and anthropomorphic factors (actual or perceived relationships between arches and humans). The most common types of natural rock openings in the Red River Gorge are (alphabetically) alcove arches, buttress arches, cave arches, pillar arches, shelter arches, and waterfall bridges.
Natural arches in the Red River Gorge form on top of and at the base of narrow, joint-bounded, sandstone-capped ridges in the cliff-forming Pennsylvanian Corbin Sandstone. Natural arches also occur in the Mississippian Newman Limestone, which forms discontinuous cliffs along the flanks of ridges and also underlies the valleys. Certain types of natural arches also occur along different parts of the landform and the landscape. Generally, shelter arches form on ridgetops, alcove and buttress arches form along the sides of cliffs, pillar arches form along the base of cliffs, whereas bridges span drainages and cave arches usually form in limestone.
Future work will entail refining the classification of ridgetop arches and collecting samples for OSL dating to determine possible age for arch formation and landscape evolution.