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Tectonics, fracturing of rock, and erosion

Tectonics, fracturing of rock, and erosion,10.1029/2005JF000433,Journal of Geophysical Research,Peter Molnar,Robert S. Anderson,Suzanne Prestrud Ander

Tectonics, fracturing of rock, and erosion   (Citations: 17)
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We argue that by fracturing rock, not by raising it relative to base level, tectonics plays its most important role in causing rapid incision of valleys and rapid erosion of hillslopes. Tectonic deformation riddles the upper crust with fractures, which not only provide avenues for water flow and thus promote weathering and further disintegration of rock but also fragment bedrock into debris that is readily extracted and transported by surface processes. Bends in active faults require straining of adjacent rock masses. Aftershocks that occur subsequent to slip on primary faults reflect penetrative brittle deformation of the upper crust. At least some aftershocks must nucleate or lengthen cracks, which contribute to the comminution of these rock masses. Scaling rules suggest that dimensions of ruptures for very small (M < -2) earthquakes can be meters or less. The Gutenberg-Richter recurrence relationship implies that such earthquakes are common, as high-magnification seismographs in low-noise environments confirm. Moreover, large differences among fault plane solutions for aftershocks show that the small faults on which they occur are not parallel to one another; some faults must intersect. Thus the upper crust in tectonically active regions should be fragmented into blocks down to the scale of boulders or smaller. Dismembered rock arrives at the Earth's surface already prepared to be transported away. As a corollary, both deeply exhumed lower crust and posttectonic igneous rock, never deformed under brittle conditions and not deformed recently, should be less susceptible to detachment and subsequent transport than fractured rock.
Journal: Journal of Geophysical Research , vol. 112, no. F3, 2007
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    • ...Some of this correlation between rock type and denudation rate might be caused by factors other than rock composition per se. For instance, Molnar et al. (2007) suggested that fracturing is also an important control on rock strength and resistance to erosion...
    • ...These rocks often form the high-altitude core of mountain belts (Molnar et al. 2007)...

    Kevin P. Nortonet al. Cosmogenic 10 Be-derived denudation rates of the Eastern and Southern ...

    • ...Bedrock strength at hillslope scales limits topographic relief [Schmidt and Montgomery, 1995], sets thresholds for the maximum angle of slope stability [Selby, 1992; Burbank et al., 1996; Montgomery, 2001], and influences bedrock erodibility [Gilbert, 1877; Carson and Kirkby, 1972; Stock and Montgomery, 1999; Duvall et al., 2004; Molnar et al., 2007]...
    • ...In addition to influencing hillslope stability, fractures that disintegrate rock fragments or severely weaken the rock mass also produce near‐surface material that is far more readily removed by erosive processes than is pristine, intact rock [Gilbert, 1877; Carson and Kirkby, 1972; Molnar et al., 2007]...
    • ...As tectonic forces fold and bend rocks, bedrock fractures form in order to accommodate the imposed strain [Molnar et al., 2007]...

    Brian A. Clarkeet al. Quantifying bedrock-fracture patterns within the shallow subsurface: I...

    • ...Several hypotheses have been put forward for explaining the generation of steps and overdeepenings: variations in glacier length over multiple climate cycles, tributary junctions, variations in lithology or rock resistance and inherited tectonic patterns (MacGregor et al. 2000; Anderson et al. 2006; Molnar et al. 2007)...

    Olivier Le Rouxet al. Interaction between tectonic and erosion processes on the morphogenesi...

    • ...The damage that we infer is probably in the form of widelyspaced fracturing at the 5–20 cm scale, as described by Molnar et al. (2007), as opposed to pulverization which occurs at the tens of microns scale and is thought to be a marker for preferred propagation direction (Dor et al., 2006a; Lewis et al., 2007)...

    Neta Wechsleret al. Application of high resolution DEM data to detect rock damage from geo...

    • ...Fracturing should promote the disintegration of bedrock and may ultimately lead to enhanced weathering, which is the first step in the erosion process preceding the transport of material (e.g. Gilbert, 1877; Molnar et al., 2007)...

    California M. M. Goethalset al. Determining the impact of faulting on the rate of erosion in a low-rel...

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