Fluting (geology)

About: Fluting (geology) is a research topic. Over the lifetime, 44 publications have been published within this topic receiving 1293 citations.

River incision into bedrock: Mechanics and relative efficacy of plucking, abrasion and cavitation

Abstract: Improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed. We present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion (e.g., plucking, abrasion, cavitation, solution) is a strong function of substrate lithology, and that joint spacing, fractures, and bedding planes exert the most direct control. The relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks, and their spatial distributions. We find that plucking dominates wherever rocks are well jointed on a submeter scale. Hydraulic wedging of small clasts into cracks, bashing and abrasion by bedload, and chemical and physical weathering all contribute to the loosening and removal of joint blocks. In more massive rocks, abrasion by suspended sand appears to be rate limiting in the systems studied here. Concentration of erosion on downstream sides of obstacles and tight coupling between fluid-flow patterns and fine-scale morphology of erosion forms testify to the importance of abrasion by suspended-load, rather than bedload, particles. Mechanical analyses indicate that erosion by suspended-load abrasion is considerably more nonlinear in shear stress than erosion by plucking. In addition, a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued. Cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive, unjointed rocks that is otherwise attributed to suspended-load abrasion. Direct field evidence of cavitation erosion is, however, lacking. In terms of the well-known shear-stress (or stream-power) erosion law, erosion by plucking is consistent with a slope exponent ( n ) of ∼2/3 to 1, whereas erosion by suspended-load abrasion is more consistent with a slope exponent of ∼5/3. Given that substrate lithology appears to dictate the dominant erosion process, this finding has important implications for long-term landscape evolution and the models used to study it.

Reevaluation of the Lindenmeier Folsom: a Replication Experiment In Lithic Technology

Abstract: This article reports on a continuing study of the stoneworking technology of the Lindenmeier Folsom. Production time, sequential stages of manufacture, and fluting technique are examined and discussed on the basis of extensive replication and experimentation, as well as of macroscopic and microscopic analysis of one of the original Lindenmeier Folsom assemblages. Results of this study indicate that simplicity of technique, along with desired form, were crucial factors in the decision making associated with the production of the Lindenmeier Folsom.

The Forms of Glacial Erosion

Abstract: Glacicl erosion is universally attributed to two processes — abrasion and plucking — and though satisfying explanations in physical terms have yet to be offered of the mechanics of either, their reality and their general characteristics are not in doubt. Abrasion is self-evidently witnessed by polished and striated surfaces, by fluting and streamlining and by such distinctively original forms of ice-moulding as roches moutonnees. Plucking is evidenced in a variety of ways. There is G. K. Gilbert’s (1910) argument that in southern Alaska where there is clearly evidence ‘of an enormous amount of glacial degradation, it was a matter of surprise to find the reduction of the surface to smooth sweeping curves was a somewhat rare phenomenon. By far the greater number of exposed glaciated areas, even where degradation has been profound, abound in low embossments and in more or less angular groins or re-entrant spaces showing little trace of abrasive action.’ This is equally true elsewhere. There is J. P. Dana’s argument (cited in Gilbert, 1910, p. 207) that the blocks and boulders in the moraines of the Laurentide ice sheet, which received no falling stones from mountain peaks, must have been plucked bodily from the underlying bed. In Britain this argument is best exemplified by the blocks of Silurian grit that have been torn from the floor of Crummack Dale and carried uphill to rest on the limestone scar that overlooks the Craven fault. But plucking has its most conspicuous results in the cliffs of conies, though as late as 1896 E. Richter thought that because such cliffs show no signs of abrasion they were not glacially sculptured but fashioned by frost weathering above the surface of the ice.

Stream Fluting and Stream Erosion

Abstract: Swiftly moving sand or silt-laden water currents sometimes abrade grooves, elongated in the direction of flow, in stream boulders and in the bedrock of the stream channel. Discontinuous grooves of irregular pattern result from turbulence of the water flow. In this article the grooves are termed "flutes," and the process of their formation is called "stream fluting." The importance of stream fluting in fluvial erosion is discussed. The process is analyzed on the basis of excellent examples observed in the inner gorge of the Grand Canyon of the Colorado River.