Disturbance

RFP01 Properties of large hillslope blocks and cliff faces along the cottonwood limestone near the konza prairie nature trail

Abstract: 

This data is a collection of point observations and measurments of large rock fragments on grassland hillslopes. Data was collected from 30 hillslope transects that extend downslope perpidicular from the bedrock cliff formed from the Cottonwodd limestone. Transects are 30 meters long and 1 meter wide.  Observations of blocks include properites such as size, shape, and surface weathering. This data set also includes observtions of cliff properties associated with each transpect location. Measurments we made in field by hand for rock fragments larger than pebble (>64mm).

Core Areas: 

Data set ID: 

158

Short name: 

RFP01

Purpose: 

To quantify how the properties of large rock blocks (boulders) influence their movement and transport downslope on low gradient soil manteled hillslopes.

Methods: 

Location:
We studied a prominent limestone bench formed from the Cottonwood Limestone and hillslopes below the cliff. This occurs along the natural trail portion of Konza Prarie (Nature Trail  & K1A). The studied section of cliff mainly faces south and east, with some sections facing north.The study cliff formed by the Cottonwood Limestone and the hillslope under it are covered by mostly grassland and some forest. Forested sections are occupied by a combination of trees and dense woody underbrush that grow on top of and in the fractures of the cliff face and around the blocks on the hillslope under it.

Frequency of Measurment:
Properties of the Cottonwood Limestone cliff and blocks on the hillslopes under it were recorded every ~25 m for a 2 km distance along the cliff, excluding locations near trails.

Variables Measured:
Hillslope Block - Size, shape, surface weathering, block emedding, block stability, block dip.
Cliff Surface - Fracture spacing, surface weathering, height

Field Methods:
Block properties were measured for all blocks in a 30 m long, 2 m wide transect straight down the slope from the cliff face formed by the Cottonwood Limestone.  Block measurments were performed by hand and visual assement. A set of four cliff measurements were collected for each location separated by 2 m to capture local variability. Block and cliff measurments were performed by hand and visual assement. Minimum block size observed was set at 64 mm (corresponding to a 0.004 m2 surface area).  This minimum represents the cut off between pebble and cobble sized rock fragments and represents the smallest grainsize that can be easily observed in the grassy study location. Distances between all blocks and the overlying cliff were measured along the transect line from the center of the slope block. Block size was recorded as two measurements: the length of the longest and intermediate axes of the block. Each axis was perpendicular to the other. Weathering state was assessed visually as the percentage of the visible block surface that was occupied by surface pitting or spalling. Block dip in the downhill direction was measured in degrees using a digital inclinometer placed at the center of the block.Additionally, qualitative observations of stability, burial, and embedding were recorded to deduce transport processes. Block stability was recorded as stable or unstable depending on if movement or rotation resulted from the force of a human foot pushing the block. Burial condition was based on how embedded a block was in soil. The perimeter of embedded blocks was probed with either a soil knife or rock hammer to estimate the depth at which the bottom of the block occurred and in extension how much of the block was buried below the soil surface. If at least 50% of the block’s short axis was embedded, then a block was described as buried in soil. Blocks that were less than 50% embedded were recorded as unburied. For blocks that are buried, a secondary designation was given based on how the block was embedded. If a block was surrounded by soil, it was recorded as buried on all sides, whereas blocks only buried on the upslope or downslope faces were recorded as such.  Blocks were catigorized by shape  into classes of cubic and tile-shaped. A total of 30 slope block survey transects were performed, resulting in a total of 842 block observations.

 

Data sources: 

Maintenance: 

complete

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