Geological History of Arches National Park

English: Double Arch, a close-set pair of arch...

English: Double Arch, a close-set pair of arches located in Arches National Park in Utah, USA. (Photo credit: Wikipedia)

Arches National Park is a truly magical place where, on the first time of visiting you just stand and stare, wondering how on earth it all began. Well, hold on to your sun hats because I’m gonna’ tell you. The sculpted rocks and dramatic scenery of Arches National Park have been formed by 100 million years of erosion, with a little help from water, ice, underground salt movement and extreme temperatures. It’s a bit difficult to imagine whilst you enjoy your picnic under the bright blue sky that such violent forces were present in such a majestic landscape. Arches National Park is home to more than 2,000 arches in a large variety of sizes (see photo if you don’t believe me). Landscape Arch is the longest one, measuring a massive 306 feet across the base, the smallest official size of an arch, for it to be an arch is 3 feet across the base. You may also find it difficult to imagine that new arches are still being formed, and old arches are being systemically destroyed. The weather and erosion don’t stop for anybody, they might work slowly but their power is relentless. It has been known, too, for slabs of rock to fall from the underside of arches revealing more dramatic and sudden changes to the landscape. It’s pretty amazing to see some of those balanced rocks atop of the rock stacks too, how on earth do they do that?

Arches National Park and the Saltbed

Okay, so what’s all this about “underground salt movement”? Where does that come in to the geological history of Arches National Park? Well, Arches National Park lies on top of a salt bed, an underground salt bed which is, to be honest, mostly responsible for the wonderful shapes and landscape you can see – the arches, the spires, the balanced rocks, the eroded monoliths. In some places this saltbed is literally thousands of feet thick, it’s been there for around 300 million years, ever since the sea flowed into the area before evaporating, leaving the massive salt deposits behind. This salt bed was gradually covered with residue from winds, the comings and goings of oceans, floods etc (it took millions of years for that to happen), and then lots of the debris was eventually compressed to become rock.

The problem with salt is that it’s pretty unstable (try building a salt mountain on the dinner table, then squishing it), and pretty soon (well, millions of years is pretty soon geologically speaking) the weight of the rock covering the saltbed was just too much for it to handle so it started to shift, buckle, liquify, dropping whole sections into cavities and upward thrusting others. Vertical cracks started to develop helping to eventually form many of the arches in Arches National Park. Water began to seep into the cracks, ice formed, expanding and splitting the rocks, bits and pieces started to break off, you know how it goes . . .

Arches National Park Winds

Next come the winds, blowing away the loose particles leaving free-standing fins reaching from the earth. The wind and water continually attacked the fins until, in many cases, great chunks of materials gave way and the rocks tumbled out, some of the fins simply couldn’t take the strain and completely collapsed – others survived and became the famous arches.

So, that’s how the famous arches of Arches National Park were formed, in a nutshell, over hundreds of millions of years.

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