User:Hannahcl99/Arches National Park

Arch Formation
Geological processes that occurred over 300 million years ago caused a salt bed to be deposited, which today lies beneath the landscape of Arches National Park. Overtime, the salt bed was covered with sediments that eventually compressed into rock layers that have since been named Entrada Standstone. Rock layers surrounding the edge of the salt bed continued to erode and shift into vertical sandstone walls called fins. Sand collected between vertical walls of the fins, then slightly acidic rain combined with carbon dioxide in the air allowed for the chemical formation of carbonic acid within the trapped sand. Overtime, the carbonic acid dissolved the calcium carbonate that held the sandstone together. Many of the rock formations have weaker layers of rock on bottom that are holding stronger layers on top. The weaker layers would dissolve first, creating openings in the rock. Gravity caused pieces of the stronger rock layer to fall piece by piece into an arch shape. Arches form within rock fins at points of intense fracturing localization, or weak points in the rocks formation, caused by horizontal and vertical discontinuities. Lastly, water, wind, and time continued this erosion process and ultimately created the arches of Arches National Park. All of the arches in the park are made of Entrada Sandstone, however, there are slight differences in how each arch was developed. This allows the Entrada Sandstone to be categories into 3 groups including Slick rock members, Dewey rock members, and Moab members. Vertical arches can be developed from Slick rock members, a combination of Slick rock members and Moab members, or Slick rock members resting above Dewey rock members. Horizontal arches (also called potholes) are formed when a vertical pothole formation meets a horizontal cave, causing a union into a long arch structure. The erosion process within Arches National Park will continue as time continues to pass. Continued erosion combined with vertical and horizontal stress will eventually cause arches to collapse, but still new arches will continue to form for thousands of years.