Horseshoe Lake is located within Denali National Park, and is renowned for its unparalleled beauty and serene surroundings. The lake gets its name from its distinct horseshoe shaped shoreline, adding to its allure. As visitors venture along the trails that wind through lush forests and meadows, they are rewarded with breathtaking views of the lake, reflecting the majestic peaks of the Alaska Range.
While hiking along the lake, you may notice the hillside covered in loose rocks. What you are looking at is known as a scree slope, and they are fascinating geological features formed by the accumulation of loose rock fragments, typically found at the base of steep mountains or cliffs. The process of scree slope formation begins with weathering, as rocks are broken down into smaller fragments due to freeze-thaw cycles, chemical weathering, or mechanical processes like exfoliation (peeling away of sheets of rock off a rocks surface). These fragments, ranging in size from pebbles to boulders, gradually accumulate on the slope, as gravity causes them to slide or tumble downwards. Scree slopes are often found in mountainous regions where steep slopes and frequent weathering processes contribute to the continuous accumulation of loose rock material. These slopes can be highly unstable, with the angle of repose being a crucial factor in determining their stability. Heavy rainfall or seismic activity can trigger mass movements, leading to scree avalanches or landslides, further shaping and modifying the slope over time.
In geology, the angle of repose refers to the maximum slope or angle at which loose, granular materials, such as sand, gravel, or rock fragments, can remain stable without collapsing or sliding. This concept is critical in understanding the stability and behavior of natural landforms, such as hillslopes, dunes, and talus piles. The angle of repose is influenced by several factors, including the size, shape, and cohesion of the particles comprising the material. Generally, materials with larger, more angular particles tend to have steeper angles of repose, while fine-grained and rounded particles lead to shallower angles. The angle of repose can also be affected by external factors, such as the presence of water or other fluids. The addition of water can reduce the friction between particles, causing a decrease in the angle of repose, leading to landslides and other mass movements. On the other hand, dry conditions can result in a higher angle of repose, providing greater stability to the geological features.
In order to help protect the park for future generations to be able to enjoy, please remain on the trail at all times. All observations can be made without leaving the trail.
Logging Requirements:
- Describe the scree slope visible in front of you (or behind you, if facing the lake). Are the rocks rounded, or jagged? What size rocks is it made up of?
- Estimate the angle of repose. What other factors do you think can influence the angle of repose?
- Do you see any vegetation growing on the scree slope? How do you think this affects its stability? Based on your observations, do you think this scree slope is stable, or not, and why?
- Upload a photo with Horseshoe Lake. You don't have to be in the photo, though it is strongly encouraged.
Sources:
- https://www.meteorologiaenred.com/en/que-es-un-canchal.html
- https://www.allthescience.org/what-is-the-angle-of-repose.htm
- https://backyardgeology.com/2021/05/19/dig-your-toes-into-the-angle-of-repose/