Talus Behavior above Timber in the Rocky Mountains

Behre, Charles H.

doi:10.1086/624074

Cited by 36 publications

(22 citation statements)

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“…) or elsewhere (e.g. Daly 1912;Behre 1933;Sharp 1942;Blagborough and Breed 1967;Washburn 1979, p. 234). Secondly, the constituent debris is exceptionally coarse, with numerous boulders exceeding 1 m in length.…”

Section: Sissons Also Does Not Mention a Broad Low Ridge (Ef Inmentioning

confidence: 99%

Protalus rampart development and the limits of former glaciers in the vicinity of Baosbheinn, Wester Ross

Ballantyne

1986

SJG

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Synopsis J. B. Sissons’ interpretation of a massive debris accumulation at the NW end of the Baosbheinn ridge in terms of two stages of protalus rampart development is shown to be inconsistent with the field evidence, and palaeoclimatic inferences and rockwall retreat rate calculations based on this interpretation are consequently invalid. Part of the debris accumulation is reinterpreted as two lateral moraine fragments that were deposited at the southern limit of westwards-moving ice from the Loch Maree trough at the maximum of the Wester Ross Readvance, some time before c. 13,000 B.P. During the Loch Lomond Stadial of c. 11,000–10,000 B.P. two valley glaciers advanced northwards on either side of Baosbheinn into the area formerly occupied by Wester Ross Readvance ice and truncated the earlier readvance limit, thereby isolating the lateral moraine fragments on the flanks of Baosbheinn. The upper part of the debris accumulation is apparently a giant protalus rampart of Loch Lomond Stadial age, but various characteristics of this feature suggest that unlike other Lateglacial ramparts it was not formed by slow rockfall accumulation. Instead, it probably formed when a massive rockslide or series of rockslides involving failure of c. 200,000 m 3 of rock over-rode a former snowbed and accumulated as a boulder ridge that partly buried the higher lateral moraine fragment.

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Section: Sissons Also Does Not Mention a Broad Low Ridge (Ef Inmentioning

confidence: 99%

Protalus rampart development and the limits of former glaciers in the vicinity of Baosbheinn, Wester Ross

Ballantyne

1986

SJG

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“…In steep bedrock landscapes, small piles of loose grains trapped upslope of vegetation or other roughness obstacles are systematically larger and steeper where particle size approaches obstacle size [ DiBiase et al ., ; DiBiase and Lamb , ; Lamb et al ., ]. Talus accumulations with dimensions approaching the size of their constituent blocks are also common, and their slopes tend to steepen near the top [ Behre , ], suggesting a transition from bulk friction angles lower on the pile to higher friction angles at the top. Mass failures and flows including rock avalanches, dry ravel, shallow landslides, riverbed failure, and debris flows can have thicknesses that are less than a few tens of grains [e.g., Takahashi , ].…”

Section: Introductionmentioning

confidence: 99%

Force chains as the link between particle and bulk friction angles in granular material

Booth

Hurley

Lamb

et al. 2014

Geophysical Research Letters

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From sediment transport in rivers to landslides, predictions of granular motion rely on a Mohr-Coulomb failure criterion parameterized by a friction angle. Measured friction angles are generally large for single grains, smaller for large numbers of grains, and no theory exists for intermediate numbers of grains. We propose that a continuum of friction angles exists between single-grain and bulk friction angles due to grain-to-grain force chains. Physical experiments, probabilistic modeling, and discrete element modeling demonstrate that friction angles decrease by up to 15°as the number of potentially mobile grains increases from 1 to~20. Decreased stability occurs as longer force chains more effectively dislodge downslope "keystone" grains, implying that bulk friction angles are set by the statistics of single-grain friction angles. Both angles are distinct from and generally larger than grain contact-point friction, with implications for a variety of sediment transport processes involving small clusters of grains.

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“…Washburn, 1979: 234;Sissons, 1980: 20;White, 1981;Ballantyne, 1986; Ballantyne and Kirkbride, 1986). The supposed multiridged ramparts identified and illustrated by, for example, Behre (1933), Sharp (1942), Blagbrough and Breed (1967), and Lindner and Marks (1985) appear to possess characteristics more consistent with talus-foot rock glaciers than true protalus ramparts (cf. Ballantyne and Kirkbride, 1986).…”

Section: Introductionmentioning

confidence: 99%

“…Rampart development has generally been attributed to the progressive accumulation of clasts that have fallen from cliffs upslope and rolled, bounced, or slid to the foot of the firn field, a mechanism first proposed by Daly (1912: 593) and accepted by almost all later writers on the topic (e.g., Behre, 1933;Bryan, 1934;Sharp, 1942;Richmond, 1962Richmond, , 1964Blagbrough and Breed, 1967;Sissons, 1976;Washburn, 1979: 234;Veyret, 1981;White, 1981;Lindner and Marks, 1985;Ballantyne and Kirkbride, 1986). As noted by Johnson (1983), however, the validity of this mode of accumulation has never been adequately established through studies of presentday rampart development, as virtually all accounts of protalus ramparts concern relict (usually late Pleistocene examples.…”

Section: Introductionmentioning

confidence: 99%

Some Observations on the Morphology and Sedimentology of Two Active Protalus Ramparts, Lyngen, Northern Norway

Ballantyne¹

1987

Arctic and Alpine Research

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. INSTAAR, University of Colorado andThe Regents of the University of Colorado, a body corporate, contracting on behalf of the University of Colorado at Boulder for the benefit of INSTAAR are collaborating with JSTOR to digitize, preserve and extend access to Arctic and Alpine Research. ABSTRACT Previous studies of protalus ramparts have largely concerned relict examples, and the process of rampart formation has been simply assumed or inferred. Study of two actively accumulating ramparts in northern Norway demonstrates that although rockfall boulders with sufficient momentum do accumulate at the foot of perennial firn fields (as previously envisaged), deposition of avalanche debris incorporating a high proportion of fine material also contributes substantially to rampart development. The study ramparts both comprise four morphological units, each characterized by a distinctive sedimentary facies. These are (1) a gentle proximal slope underlain by an openwork mixture of rockfall boulders and smaller avalanche-transported clasts; (2) a crest over which the frequency of rockfall boulders decreases outwards such that the distal part is dominated by avalanche deposits; (3) a steep (up to 43?) unstableand approximately rectilinear distal slope underlain by a diamicton consisting of avalanche deposits from which a large proportion of clasts has been lost downslope; and (4) a basal talus comprising fall-sorted clasts that accumulated mainly by rolling down the distal slope. These findings have wider implications in terms of the correct identification and interpretation of relict protalus ramparts, and in particular help to account for the presence of abundant fines in such ramparts.

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Talus Behavior above Timber in the Rocky Mountains

Cited by 36 publications

References 0 publications

Protalus rampart development and the limits of former glaciers in the vicinity of Baosbheinn, Wester Ross

Protalus rampart development and the limits of former glaciers in the vicinity of Baosbheinn, Wester Ross

Force chains as the link between particle and bulk friction angles in granular material

Some Observations on the Morphology and Sedimentology of Two Active Protalus Ramparts, Lyngen, Northern Norway

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