Paleogeomorphology of the Sub-Pennsylvanian Unconformity of the Arbuckle Group (Cambrian-Lower Ordovician)

Kansas Geological Survey
Open-file Report 2001-55

Ground-Water Sapping

Ground-water sapping is a process that entrains soil or rock when ground-water flows through and emerges from a porous medium at a free slope surface. This leads to shear stress loss of the basal support, and failure of the overlying rock producing a retreat in valley heads and sidewalls (Luo, et al., 1997; Laity and Malin, 1985). Sapping is an erosional process that produces unique landforms. Sapped drainage systems differ from their fluvial counterparts in morphology, pattern,spatial evolution of network, rate of erosion and degree of structural control (Laity and Malin, 1985).

The Late Mississippian-Early Pennsylvanian deformation produced regional uplift of the basement on the Central Kansas uplift. Local blocks were differentially affectedproducing minor horst and graben features (Franseen, 1995). These uplifted plateaus were attacked by both karst dissolution and mass-wasting processes. Exposed joints on the plateau concentrated surface runoff, and in some cases enlarged to form channels. Precipitation was rapidly diverted into the ground -water system and flowed down the localdip of the beds. Sapping occurs locally at sites where ground-water emerges from the Arbuckle just above lithologic discontinuities (intraformational shale layers). Ground-water emerging from these seepage springs slowly removes material that provides the basal support for the cliffs and slopes. Slope failure occurs as the scarp is undermined, allowing debris to accumulate at the base of the slope. Continued scarp retreat depends on fluvial processes to effectively remove talus.

Parameter Runoff-Dominated Sapping-Dominated
Basin Shape Very Elongate Lightbulb shaped
Head Termination Tapered, gradual Theater, abrupt
Channel trend Uniform Variable
Pattern Parallel Dendritic
Downstream tributaries Frequent Rare
Relief Low High
Drainage density High Low
Drainage symmetry Symmetrical Asymmetrical
Cross-section shape V-Shape U-Shape, steep wall, flat floor
Valley width Widening downstream Relatively constant
Tributary length Relatively long Short stubby tributary
Structural control Less strong Strong
Basin area/canyon area Very high Low

Comparison of geomorphic characteristics of sapping and fluvial channels in the Colorado plateau and Hawaii (after Luo et al., 1997).

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Last updated January 2002