Natural bridge

A natural bridge is a natural formation where a rock arch forms, with a natural passageway through underneath. Most natural bridges form as a narrow ridge, walled by cliffs, become narrower from erosion, with a softer rock stratum under the cliff-forming stratum gradually eroding out until the rock shelters thus formed meet underneath the ridge, thus forming the natural bridge eg. Kolob Arch.

Natural bridges also form from natural limestone caves, where paired sinkholes collapse and a ridge of stone is left standing in between, with the cave passageway connecting from sinkhole to sinkhole.

Like all rock formations, natural bridges are subject to continued erosion, and will eventually collapse and disappear. One example of this was the double-arched Victorian coastal rock formation, London Bridge which lost an arch after storms increased erosion.

See also:

• Arches National Park
• Natural Bridges National Monument[?]
• Bridge