Mesa Arch Earthcache EarthCache

Canyonlands National Park

Over hundreds of millions of years, this area has undergone some dramatic changes. As the North American continent slowly drifted away from the equator what is now Canyonlands was flooded by oceans criss-crossed by rivers covered in mud and buried by sand The climate here has resembled a tropical coastline, a sand dune desert, and just about everything in between. And in each of those environments, sediments deposited by wind and water piled up on the surface and buried whatever lay below Dissolved minerals like calcium carbonate, then cemented these buried sediments together, turning them into layers of rock
 

Arch Formation

Unsupported spans of rock fall under two main categories, natural bridges and arches, both of which are well represented on the Colorado Plateau. Natural bridges form by stream erosion and span either an active or an abandoned water course.>
 
In contrast to natural bridges, arches form by weathering processes and are unrelated to stream erosion.
 
There are two fundamental requirements for arch formation, a narrow wall of rock known as a fin, and rocks that are strong enough to support the roof of the arch. These requirements are most often met within the Slick Rock Member of the Entrada Sandstone and the Navajo Sandstone .
 
Arch formation often begins at the contact between the Dewey Bridge and Slick Rock Members of the Entrada Sandstone. The Dewey Bridge Member, which contains shale interbeds, is preferentially eroded producing a notch or overhang. The unsupported roof of the notch spalls off forming a concave cove. Eventually as the cove enlarges it breaks through the fin to form a window which can become enlarged to form an arch.
 
There are three major stages of arch formation.
1) Development Stage; characterized by a small window relative to the mass of enclosing rock.
2) Growth Stage; characterized by thinner more delicate arches with dwindling supports.
3)Destructive Stage; collapsed arches, with only closely spaced pinnacles remaining.

Development




Pothole arches can form on the edge of vertical cliffs in the absence of a fin. Potholes form in slight depressions on the surface of exposed rocks. Water accumulates in these depressions which increases their susceptibility to weathering and causes the depressions to be enlarged. If a pothole forms near the edge of a vertical cliff, it could eventually breach the side of the cliff and become enlarged to form a pothole arch. Many of the arches in the Windows section and Mesa Arch of Canyonlands formed in this manner.

  Mesa Arch Trail

The trail to Mesa Arch is one of the easiest that you will find in the Island in the Sky district of Canyonlands National Park. It is short — about a half mile total — and has only 100 feet of total elevation gain the trail surface is mostly sand but also traverses several short sections of slickrock small rock piles mark the route.

 Please stay on the well marked paths Biological soil crust is a living ground cover that forms the foundation of high desert plant life in Canyonlands and the surrounding area. This knobby, black crust is dominated by cyanobacteria, but also includes lichens, mosses, green algae, micro fungi and bacteria.walking on them will destroy them.

Parents please keep your childern with you Mesa Arch stands on the edge of a 500ft drop cliff.

During a thunderstorm it is recommended that you return to your car keep the windows fully up

Mesa Arch Logging Requirements.

There is no Information board at the arch.

Q1   Looking at the three stages of development above at what stage do you think Mesa Arch is at now ?

Q2   What is the hard layer of sandstone you are standing on called and what do you think it used to be ?

Q3   From Mesa Arch how many other distant sandstone formations and Landmarks can you name ?

Q4 Mesa Arch is a cliff hanging arch do you think it was formed by Erosion or Weathering please explain your choice ( looking at the ground rock in the Arch area might help )

Q5 Do you think the Arch could get larger ? if yes how could this happen ? ?

Please email your answers to us through our profile