A natural arch or natural bridge is a natural geological formation where a rock arch forms, with an opening underneath. Most natural arches 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 arch. Natural arches commonly form where cliffs are subject to erosion from the sea, rivers or weathering (subaerial processes); the processes "find" weaknesses in rocks and work on them, making them larger until they break through.
The choice between bridge and arch is somewhat arbitrary. The Natural Arch and Bridge Society identifies a bridge as a subtype of arch that is primarily water-formed. By contrast, the Dictionary of Geological Terms defines a natural bridge as a "natural arch that spans a valley of erosion."
Read more about Natural Arch: Coastline, Weather-eroded Arches, Water-eroded Arches, Cave Erosion, Arches As Highways, Gallery, Notable Natural Arches
Famous quotes containing the words natural and/or arch:
“[O]ur rules can have authority over such natural rights only as we have submitted to them. The rights of conscience we never submitted, we could not submit. We are answerable for them to our God.”
—Thomas Jefferson (1743–1826)
“Men themselves have wondered
What they see in me.
They try so much
But they can’t touch
My inner mystery.
When I try to show them,
They say they still can’t see.
I say,
It’s in the arch of my back,
The sun of my smile,
The ride of my breasts,
The grace of my style.
I’m a woman
Phenomenally.
Phenomenal woman,
That’s me.”
—Maya Angelou (b. 1928)