There is no simple short answer for how arches are formed. A geologist could go on for hours describing the nuances of the process. However, since we are not official geologists and we’re assuming you aren’t either, here’s the simplest way we know how to explain the forming of an arch.
Underneath Arches National Park lies a salt bed layer, which was deposited some 300 million years ago when the area was part of an inland sea. When the sea evaporated, it left salt deposits; some areas collected over a thousand feet of these deposits. During the next millions of years, the area was filled with debris deposited from winds, floods, streams and oceans that came and went. Over time this debris compressed into rock. The weight of the rock layer caused the salt bed below to become fluid, allowing it to thrust up and create domes and ridges.
What happened after the movement of salt molded the landscape? Erosion went to work on the surface rock layers and ground water began to dissolve the underlying salt deposits. Water seeped through cracks in the weathered rock and ice formed, further expanding the crevices and weakening the rock. Eventually, the domes began to collapse leaving a maze of vertical free-standing rock walls known as fins. Wind and water continued to assault these fins until they eventually wore through and pieces began to fall away, creating the amazing arches you see today.
Free Insiders Guide to Moab, UTWhat to take, where to eat, where to stay, what to do, and a few little secrets on the side. Our Moab Insiders Guide will provide you with all the essentials for a perfect Moab experience.
Expedition GuideWhat to take, where to eat, where to stay, what to do, and a few little secrets on the side. Not unlike your own personal Jiminy Cricket, (minus the worries of the little guy getting smooshed) the Moab Insiders Guide will provide you with all the essentials for a perfect Moab experience.
