Talus Flows at The Loch EarthCache
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Rocky Mountain National Park is located west of Estes Park and north and east of Grand Lake. This is a fee area of the National Park Service, and costs $30 per vehicle. This fee is covered in the Rocky Mountain National Park Annual Pass, the Rocky Mountain National Park/Arapaho National Recreation Area Annual Pass, and the America the Beautiful Pass. Please see the following website (visit link) for the entire fee schedule. The park is open 24 hours a day, 365 days a year. Road and Trail Conditions and Closures can be found at: (visit link) Recorded information for the condition of Trail Ridge Road can be found by calling (970) 586-1222. Please remember that all geologic features within the borders of Rocky Mountain National Park are protected by law, as are all natural and historic features. Please do not disturb, damage, or remove any rocks, plants, or animals.
This EarthCache is located on the point that juts out from the north shore of The Loch, a high elevation lake formed from the waters of Icy Brook. The steep walls on the east and west sides of The Loch are formed from biotite schist and gneiss, and age to about 1.7 billion years old. Erosion has caused several talus flows to form on the eastern wall (to the left as you look south across The Loch), and these talus flows will be the subject of this EarthCache. Because loose fragments of rock are continually rolling downslope and shifting position, you should not attempt to go near these slopes!
Talus is the accumulation of loose pieces of rock and rock fragments that fall from cliffs and collect in fan-shaped piles at the base of the slopes. This type of erosion is more common in arid areas due to the general lack of vegetation that might hold the soils in place. Weathering actions of heavy rains and freeze-thaw actions are the primary causes of talus slopes, with the resulting rockfalls and debris flows being responsible for the movement of the material.
Talus slopes in the Park are relatively recent in age (from the Holocene and upper Pleistocene), with all of the alpine and sub-alpine talus occurring after the retreat of the most recent glaciers around 10,000 years ago.
Note that the slopes of the talus flows are similar. All of the flows are at the Angle of Repose, which is the steepest angle that will be supported by the underlying material. This is one of the reasons that talus slopes can be dangerous, since any movement on the slope can cause additional unpredictable downhill rock movement.
To receive credit for this EarthCache, send me an email with the answers to the following questions:
1.) How many talus slopes do you see on the eastern wall?
2.) From this location, estimate the angle of repose for these talus slopes.
3.) Do you think the rate of accumulation of the talus is greater now, or right after the glaciers retreated? Explain your answer.
Please consider posting photos of yourself, or the local geology, when you log this EarthCache. Photos can be an additional rewarding part of your journey, but posting them is not a requirement for logging this EarthCache, and is strictly optional.
The above information was compiled from the following sources:
2004. Rocky Mountain National Park. In Harris, A.G. et al., editors. Geology of National Parks, Sixth Ed. P. 337-356. Dubuque, Iowa: Kendall/Hunt Publishing Company.
Cole, J.C., and Braddock, W.A. 2009. Geologic map of the Estes Park 30’ x 60’ quadrangle, north-central Colorado: U.S. Geological Survey Scientific Investigations Map 3039, 1 sheet, scale 1:100,000, 1 pamphlet, 56 p.
KellererLynn, K. 2004. Rocky Mountain National Park. Geologic Resource Evaluation Report. NPS D307, September 2004. Online at: (visit link)
Rocky Mountain National Park. Online at: (visit link)
Rocky Mountain National Park was most helpful in the background discussion, aid in the choosing of sites, and review of this EarthCache. My thanks to the Park for allowing the placement of this EarthCache!
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