Arid Arches

It is well known that Arches National Park is located in an arid landscape, but what exactly does that mean? Most people think of desserts when they hear the world arid and though this tends to be true is not 100%. The word Arid simply means that the land receives less than 8 inches of rain fall per year. witch tends to result in less than 25% plant cover.

Arches Dry weather truly changes it landscape. The most common plant throughout Arches is the Juniper Tree. All plants in arid climate have extreme adaptations that let them survive. The Juniper is a desert expert; the trees send there roots out wide rather than deep to collect the most water when is does rain. when these trees are only 6ft tall they can be 100's of years old. The rest of the ground in Arches is simply covered in small low lying shrubs.

Arches lies in the center of the Rocky Mountains this Causes a rain shadow all over the Great Basin. The water in the clouds is deposited on the mountains before reaching The Great Basin creating its arid landscape.

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Arches resides in one of the most arid desert in the United States. Although the Great Basin might seem like a  fairly consistent place for weather on a short visit, the weather here can change in a instant.

As arches resides in a desert there is not a lot to retain the heat from the day. In the summer the temperature can sore over 100 F at mid day, however at night the temperature plummets towards freezing. Not many people realize that Arches can get some fairly strong snow storms.

Although arches is a desert the most dangerous weather here is water. Flash floods are due to thunder  storms that can be miles away. The earth around arches is scared with small gullies that run for miles many hikers have been walking through these canyons on perfectly sunny days when out of no were a wall of water is bearing down on them. Flash floods are unpredictable at best you might know they are coming just a few seconds before it arrives. Notice in the picture below the flat lands are flooding but there is no rain and the clouds above aren't major storm clouds. Arches my gets quite a few thunder storms a year, however most precipitation will fall in a single storm making flooding a serious danger.  

Weathering

The most important force that shaped Arches National Park is weathering. Without weathering Arches would be nothing more that a pile of rocks and one of the elegant structures could have formed.

  Notice in the photo above the large boulders laying on the ground in Double Arch. Arches was formed to to the expiation of a great salt dome. Due to this salt dome the sands and rocks in Arches have a large amount of salt. When salt partials heat and cool they expand and contract more than stones this causes small or large peaces of rock to begin to break away.

Salt Particles

Although most weathering in Arches is due to Salt it is not the only form. If an arch forms in a spillway it is actually not and arch but rather a natural bridge. A bridge plain and simple is a arch formed by running water. 

The final form of weathering that affects arches is wind weathering, however wind is often given more credit than it has earned. Wind can smooth out the base of rocks by beating sand off the stones, however the wind can only lift the sang a few feet from the ground. Wind itself is only causes minor weathering.

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Arches National Park resides in the center of Utah just outside of Moab. The park itself is only 119 square miles for comparison Yellowstone National Park is 3,468 square miles. Although the park is dwarfed by some of its cousins it holds some of the most spectacular sights that have ever been seen.

Arches delicate and beautiful rock formations are made almost completely from sandstone. Sandstone is a Sedimentary Rock made almost completely out of you guessed it sand. Sandstone is comprised mostly of Feldspar and Quartz however Arches Sandstone also has a high amount of Iron giving it its reddish tint. Sedimentary rock is formed in layers called Strata witch can be clearly seen in the image above by looking for the horizontal lines in the rock. Sedimentary rock always forms underground with heat and pressure so the rocks that you see have remained as the earth surrounding them eroded away this allows for some very impressive structures to form.

The Delicate sand stone sits lightly atop some major faults the most famous being the Moab Fault.(shown above) This fault cause the valley (in witch the city of Moah resides) to drop almost 2500 feet form the surrounding landscape truly shaping the park.

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this blog in by John Rugg it is on Arches National Park