This EarthCache is located in Great Smoky Mountains National Park and was placed with permission from NPS. There is no container to find and no need to leave the trail.
From the parking lot, you will hike on the Alum Cave Trail for about 1.5 miles until you reach Arch Rock. You will gain about 1200 ft in elevation so be prepared for a tough hike and bring plenty of water and food.
Arch Rock is located in a rib of black slate that is slanting down from the slope to the Styx Branch Creek below. The trail crosses the creek on a log bridge and continues under the arch. This will give you the opportunity to examine the rock closely and learn how this arch was formed. At the lower point of the arch, the hole is about 20 feet wide. But at the upper portion, it is about 6 feet wide. So how did this arch form?
An arch typically forms through an erosion process. It can be done by wind or water/ice. The softer rock erodes away as the water or wind can widen the cracks in the rock. As ersoion undercuts the rock material, it will cause the rock to collapse. Flowing water can erode the rock as the water passes by. This typically will have smoother edges.
Arches can also form through freeze-thaw weathering. The rock contains small holes that can allow water to pass through. This also occurs at bedding planes. When temperatures drop, the water will freeze and expand. This expansion causes the cracks to widen. And as the cracks widen, more water can make it deeper into the cracks. The process will repeat itself until the rock splits entirely. Along the bedding planes you will notice more blocked edges, rather than a smoother surface.
Logging Tasks:
1. Post a picture of you (face not required) or a personal item at Arch Rock.
2. Explain in your own words how this arch formed.
3. Do you think the arch will continue to grow or stay the same size? Why or why not?