![]() At that time, the park was a little-known and seldom-seen national monument.Īrches has changed dramatically in the years since it became a national park in 1971: The roads are paved, the campground has flush toilets, and at least 43 arches have collapsed. In 1968, Arches park ranger Edward Abbey wrote Desert Solitaire: A Season in the Wilderness, his ode to Arches and the one book I would choose to keep me company if I were marooned on a desert island. “Our best guess is that the smaller arches are on the order of hundreds to thousands of years old, while the largest arches may be in the range of 100,000 years old.” Ever Changing Arches Erosive features are notoriously hard to date, he said, because most of the diagnostic evidence is transported away by wind and water. Arches naturally erode into self-supporting shapes with the weight of the overlying rock compressing the base of the structure into a strong abutment, much like how the thick base of a stone wall supports the arched roof of a cathedral.Įntrada sandstone dates back to the time of the dinosaurs, but the arches themselves are much younger, with most existing arches likely forming within the past few thousand years.Įntrada sandstone dates back to the time of the dinosaurs, but the arches themselves are much younger, with most existing arches likely forming within the past few thousand years, said Paul Geimer, a geophysicist at the University of Utah in Salt Lake City. Once a hole forms, chunks of rock fall from the ceiling, enlarging the opening, in some places creating arches more than 90 meters across.Īrches come in many shapes and sizes, but they all follow the same engineering principles that govern bridges and cathedrals: Certain shapes, especially circles and arcs, are stronger than others. As water flows over and around these fins, weaker areas of rock will erode away faster, sometimes creating an alcove or shallow cave that eventually wears into a hole through the fin. Originally laid down in the Jurassic period between 180 and 140 million years ago as sand dunes and beaches, this coppery orange sandstone is relatively soft and readily sculpted by flowing water, as well as freeze and thaw cycles.Īround Arches National Park, the Entrada layers tend to erode into fins along parallel fractures, setting the stage for arches to form over thousands of years. If the catalog is expanded to include smaller arch openings, over 2,000 can be found within the 310-square-kilometer park.Īrches can form in many types of rock, but around Moab, Entrada sandstone is the star. How Old Are Arches?Īrches National Park, near the town of Moab, boasts around 100 arches with openings that span at least 1 meter across. But don’t despair-although all the famous arches will crumble and collapse within a few thousand years, replacements will continue to be sculpted out of Utah’s bedrock for a very long time to come. On geologic timescales, Delicate Arch will exist for only the blink of an eye. Most people know Utah’s most famous rock feature, Delicate Arch, from the state’s license plate and the America the Beautiful commemorative quarter, but if you’ve ever hiked to its bow-legged base in Arches National Park, you know it’s really not all that delicate: The soaring 16-meter-high arc of Entrada sandstone is the largest freestanding arch in the park.
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