Effect of height and orientation (microclimate) on geomorphic degradation rates and processes, late-glacial terrace scarps in central Idaho

Pierce, Kenneth L.; Colman, Steven M.

doi:10.1130/0016-7606(1986)97<869:eohaom>2.0.co;2

Cited by 122 publications

(119 citation statements)

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“…These first two estimates are based on the simple morphologic assumption that the last large regional alluvial discharge occurred near the onset of the Holocene period, 10 ±2 kyr ago. The three values we found for k in three regions of northwestern China are in fair agreement with those obtained for similar scarps under semi arid climates in the western United States [Colman and Watson, 1983;Hanks et a!., 1984;Pierce and Colman, 1986;Hanks and Wallace, 1985]. Profl!ill>:e_O~ff.,_se"'t~ .…”

Section: Calibrationsupporting

confidence: 75%

“…The product of the numerical age by the mass diffusivity constant kt can be estimated directly from one scarp, using equation (5) and measurements of the regional slope, half offset, and maximum scarp slope (see, for example, Nash [1980a] or Pierce and Colman [1986]). If a set of profiles presumed to be of the same age and of various heights is available, Hanks et al [1984] suggest plotting the reduced scarp slope tge-b as a function of the scarp half offset.…”

Section: Diffusion Model Of Scarp Degradationmentioning

confidence: 99%

“…Unfortunately, it seems that for scarps formed in similar cohesionless materials and under a , similar semiarid climatic environment, the mass diffusivity constants can vary by a factor of .ten, between 1 and 11 m2jkyr (Table 1). Pierce and Colman [1986], for example, have carried out a study of a set of terrace risers of known ages in Idal10 to explore the dependency of the mass diffusivity constant 9n ·climatic, geologic and even geometric factors. That study .showed a conspicuous dependency of mass diffusivity on scarp orientation as well as a clear pos1t1ve correlation between apparent mass diffusivity and scarp height (see also Colman and Watson [1983] and Hanks et al [1984]): k is seen to vary between 0.7 and 5.2 m2Jkyr for scarps about 10-15 m high, and between 0.3 and 1.6 m2Jkyr for scarps about 5 m high.…”

Section: Diffusion Model Of Scarp Degradationmentioning

confidence: 99%

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Analysis of scarp profiles: Evaluation of errors in morphologic dating

Avouac¹

1993

J. Geophys. Res.

103

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Morphologic analysis of scarp degradation can be used quantitatively to determine relative ages of different scarps formed in cohesionless materials, under the same climatic conditions. Scarps of tectonic origin as well as wavecut or rivercut terraces can be treated as topographic impulses that are attenuated by surface erosional processes. This morphological evolution can be modelled as the CQ!lvolution of the initial shape with erosion (or degradation) function whose width increases with time. Such modelling applies well to scarps less than !Om high, formed in unconsolidated fanglomerates. To a good approximation, the degradation function is Gaussian with a variance measuring the degree of rounding of the initial shape. This geometric parameter can be called the degradation coefficient. A synthetic experiment shows that the degradation coefficient can be obtained by least squares fitting of profiles levelled perpendicular to the scarp. Gravitational collapse of the free face is accounted for by assuming initial scarp s~opes at the angle of repose of the cohesion less materials (30° -35°). Uncertainties in the measured profiles result in an uncertainty in degradation coefficient that can be evaluated graphically. Because the degradation coefficient is sensitive to the regional slope and to three-dimensional processes (gullying, loess accumulation, stream incision. etc.), a reliable and accurate determination of degradation coefficient requires several long profiles across the same scarp. The linear diffusion model of scarp degradation is a Gaussian model in which the degradation coefficient is proportional to numerical age. In that case, absolute dating requires only determination of the propotionality constant, called the mass diffusivity constant. For Holocene scarps a few meters high, in loose alluvium under arid climatic conditions, mass diffusivity constants generally range between I and 6 m2/kyr. Morphologic analysis is a reliable method to compare ages of different scarps in a given area, and it can provide approximate absolute ages of Holocene scarplike landforms. lNTRODUCfiONThe geomorphic expression of an active fault is usually characterized by offsets of features such as rivers, ridges, terrace levels and terrace risers, or moraines or simply of the sloping topographic surface. The kinematics of an active fault can be constrained by measurements of such offset features, combined with dating. Measurement of offsets is a relatively simple and easy task, especially with modem digital geodetic instruments. Dating of the morphology is less straightforward. In arid and semiarid regions, organic material (such as peat or charcoal) is rare, which makes 14C dating a painstaking endeavour. Based on the use of other cosmogenic isotopes (such as 36Cl, lOBe or 26Al), of thermoluminescence or of desert varnish development, new techniques may soon allow easier accurate dating. Morphologic dating is an alternate method that derives from the simple observation that the shape of a scarp is a function of its age [Wall...

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Section: Calibrationsupporting

confidence: 75%

Section: Diffusion Model Of Scarp Degradationmentioning

confidence: 99%

Section: Diffusion Model Of Scarp Degradationmentioning

confidence: 99%

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Analysis of scarp profiles: Evaluation of errors in morphologic dating

Avouac¹

1993

J. Geophys. Res.

103

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“…The scarp-morphology data presented in the following discussion show the relation between fault-scarp height and maximum scarp-slope angle, the variation of these two parameters, and their relation to fault scarps of known age. My studies are based on the following premises of fault-scarp evolution: (1) initially, the free face of the fault scarp is near vertical, reflecting the near-surface dip of the fault; (2) soon the face slumps to the angle of repose of the faulted material, typically 32°-35° for unconsolidated surficial deposits; and (3) then the slope of the scarp decreases at a slower rate, mainly by the process of slopewash instead of gravitional collapse (Wallace, 1977;Nash, 1981 ;Pierce and Colman, 1986). Only those fault scarps on unconsolidated Quaternary deposits have been analyzed.…”

Section: Fault-scarp Morphologymentioning

confidence: 99%

Preliminary assessment of Quaternary faulting near Truth or Consequences, New Mexico

Machette¹

1987

Open-File Report

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“…Underlying deposit characteristics suggest fluvial transport and sorting from sheetfloods have been the dominant transport processes (Pierce and Scott, 1982;Patterson, 2006). This has produced deposits composed of clast-supported gravels with planar to sub-horizontal bedding and low percentages of silt and clay (Funk, 1976;Pierce and Scott, 1982;Pierce and Colman, 1986;Patterson, 2006). Alternating coarse to fine couplets characteristic of sheetfloods (Blair and McPherson, 1994) are common.…”

Section: Insert Figure 2 Herementioning

confidence: 99%