NOTE: PER PARK MANAGEMENT REQUEST, YOU MUST NOT PARK DIRECTLY AT GZ. THIS IS VERY DANGEROUS AND YOU CAN BE TICKETED FOR DOING SO. PARKING IS AVAILABLE ABOUT 250-300 FEET EAST ON THE NORTH SIDE OF THE ROAD.
From Ground Zero, you will observe a very rough hillside down below the roadway. This is one of the Niobrara State Park Landslides. To qualify for logging this Earthcache, you will need to observe the rough hillside and determine some information about this area and the underlying geological causes of this rugged hillside.
CAUTION: IT IS NOT CONSIDERED SAFE TO CLIMB DOWN THROUGH THE ROUGH AREA; MAKE YOUR OBSERVATIAONS FROM THE ROADWAY EDGE AND FROM THE INFORMATION PRESENTED IN THE FOLLOWING TEXT.
The predominant layers of earth/rock in the Niobrara State Park area are:
Sand-Silt Clay which is a soil deposited by flowing water. The material has sunk to the bottom of a river or pond. In this area, the silt covering hilltops is the remnants of material deposited many thousands of years ago by flowage in an inland sea. This soil is a loose sedimentary material with rock particles usually 1⁄20 millimeter or less in diameter and the soil contains 80 percent or more of such silt and less than 12 percent of clay.
Loess Soil is a non-layered, geologically recent deposit of silty or loamy material that is usually buff or yellowish brown in color that is deposited chiefly by the wind. Loess is a sedimentary deposit composed largely of silt-sized grains that are loosely cemented by calcium carbonate, and it is usually a homogeneous and highly porous soil. It may be traversed by vertical capillaries that permit the sediment to fracture and form vertical bluffs.
Limestone is a rock material made from ocean organisms. The layer consists of a sedimentary rock formed from the skeletons and shells of ocean organisms, and it consists chiefly of calcium carbonate.
Shale is a layer of rock that is a laminated (layered) and which is composed with more than 2/3 of the material being clay sized particles. It is often black or near black in color and may have an oily appearance.
TYPES OF LANDSLIDES: Information for this earthcache was gleaned from a research paper dealing with landslides along and near Nebraska roadways.
Rock Falls: Rock falls are a form of landslide occurring where earthen material is found below a steep slope or cliff, above an eroding cliff or valley wall, or under an undercut stream bank. In Nebraska, Rock Falls usually occur in the Greenhorn Limestone of the Cretaceous age, in Permian or Pennsylvanian aged rocks, or in rocks of the Arikaree and Ogallala groups of the Tertiary age. Landslide rubble is normally heavily laden with large, exposed, visible rock deposits. Only one roadside landslide of 209 slides studied was classified as a Rock Fall Slide.
See Figure 1 below.
Earth Slumps: Earth Slumps are defined as slumps of non-bedrock deposits (i.e. not of a bedrock material source). Typical materials forming an earth slump are loess soils, glacial materials, etc. Downward movement of the slide material is along a rotational failure plane. Of 209 landslides inventoried along Nebraska highway, 108 were classified as earth slumps.
See Figure 2 below.
Rock Spreads: This type of slide is defined as slabs or blocks of bedrock material that moves without a well-defined underlying surface upon which the material shifts. Examples in Nebraska have been observed involving Cretaceous Greenhorn limestone. Only one example of this type of slide has been observed in Nebraska.
See Figure 3 below.
Rock Slumps: This type of slide is defined as a mass of bedrock that moves down slopes on a rotational failure plane. In Nebraska, a majority of these rock slumps occurred the layer of Pierre Shale of the Cretaceous age. Seventy of the 209 landslides documented along Nebraska roads were of this type.
See Figure 4 below.
Complex Slides: In this example, the slide is based on one or more of the previous types of landslides. Although one mechanism may dominate, more than one basic mode of failure is observed. Slides such as these often occur near major river bluffs and involve younger geological material overlaying older bedrock such as the Pierre Shale of the Cretaceous age.
See Figure 5 below.
After studying the previous descriptions of slides in Nebraska, answer the following questions to qualify for loggings requirements of this Earthcache.
1. After visually inspecting the area, what type of slide appears in this area?
2. What is the elevation above this slide?
3. What is the appearance of the surface of this slide?
4. On which side (North, South, East, West) of the road is the location of this slide adjacent?
Reference Source:
“Landslide Inventory Along Nebraska State-Federal Roadway System” by Duane A. Eversoll, CSD Research Geologist, 1991.