Research Article| February 01, 1988 Bedload sheets in heterogeneous sediment Peter J. Whiting; Peter J. Whiting 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 Search for other works by this author on: GSW Google Scholar William E. Dietrich; William E. Dietrich 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 Search for other works by this author on: GSW Google Scholar Luna B. Leopold; Luna B. Leopold 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 Search for other works by this author on: GSW Google Scholar Thomas G. Drake; Thomas G. Drake 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90024 Search for other works by this author on: GSW Google Scholar Ronald L. Shreve Ronald L. Shreve 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90024 Search for other works by this author on: GSW Google Scholar Author and Article Information Peter J. Whiting 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 William E. Dietrich 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 Luna B. Leopold 1Department of Geology and Geophysics, University of California, Berkeley, California 94720 Thomas G. Drake 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90024 Ronald L. Shreve 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90024 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1988) 16 (2): 105–108. https://doi.org/10.1130/0091-7613(1988)016<0105:BSIHS>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Peter J. Whiting, William E. Dietrich, Luna B. Leopold, Thomas G. Drake, Ronald L. Shreve; Bedload sheets in heterogeneous sediment. Geology 1988;; 16 (2): 105–108. doi: https://doi.org/10.1130/0091-7613(1988)016<0105:BSIHS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin, migrating accumulations of sediment, and coarse grains cluster at their leading edge. These accumulations are one or two coarse grains high and are much longer (0.2-0.6 m long in sand; 0.5-2.0 m in fine gravel) than their height. We propose the term "bedload sheet" for these features, and we argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment. In essence, coarse particles in the bedload slow or stop each other, trap finer particles in their interstices, and thus cause the coarse particles to become mobile again. Bedload sheets develop on the stoss side of dunes, causing the dune to advance incrementally with the arrival of each sheet. Successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain-size sorting that distinguishes cross-bedding. Available flume experiments and field observations indicate that bedload sheets are a common, but generally unrecognized, feature of heterogeneous sediment transport. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Abstract In the summer of 1962 a completely portable and relatively simple electrically heated thermal core drill of new design was constructed and used to obtain 16 oriented samples of ice 2.5 cm. in diameter by 120 cm. in length from depths ranging from 12 m. to 137 m. in lower Blue Glacier, Mount Olympus, Washington, U.S.A. The thermal element is a 0.260-in. (0.66-cm.) diameter 300-W. 150-V. tubular heater bent to form an annulus with an external diameter of 5.0 cm. Opposed ratchet-like teeth break off and hold the core inside the tubular core barrel. Orientation is recorded photographically by a commercial inclinometer modified to show azimuth and to be controlled from the surface.
Abstract In 1957 through 1962 six deep holes were drilled by means of specially developed electrically powered hotpoints, 4 cm diameter aluminum pipes were placed in them, and annual inclinometer surveys were made to investigate the deformation field and flow law of the ice at depth. Although a strongly maritime climate with moderate temperatures implies that lower Blue Glacier should be temperate, freezing at depths as great as 200 m, sometimes even in summer, seriously hindered inclinometer surveys. This freezing cannot be due solely to chilling by winter cold and to leakage into initially dry pipes, but may also be due to wintertime changes of water Table in the glacier and to contamination of the ice by antifreeze. Another possibility, residual subfreezing zones carried down from the ice fall, seems unlikely. Because the relatively inextensible pipe slips lengthwise in the deforming hole, observations of pipe motion at best give only the two components of ice velocity perpendicular to the hole. Thus, a single hole gives two independent equations connecting the nine unknown derivatives of the velocity components; two holes give four equations: and three or more give at most six. Incompressibility of the ice, when applicable gives another. The remaining unknowns must be either neglected or estimated from assumptions about the flow field. At the Blue Glacier holes the longitudinal strain-rate is less than about 0.01 per year, becoming more extensional down-glacier and more compressional at depth, because the holes were moving through a reach in which the surface steepens and the bed becomes more steep-sided and flat-bottomed. Although the effective strain-rates are only about 0.01 to 0.1 per year, so that errors are relatively large, they are in reasonable agreement with flow laws deduced from laboratory experiments by Glen, from tunnel contraction by Nye, and from deformation of Athabasca Glacier bore holes by Paterson and Savage, except that in the range of strain-rates covered the viscosities found for Blue Glacier are about half those derived from the other studies.
Motion pictures taken at Duck Creek, a clear stream 6.5 m wide and 35 cm deep near Pinedale, Wyoming, provide detailed, quantitative information on both the modes of motion of individual bedload particles and the collective motions of large numbers of them. Bed shear stress was approximately 6 Pa (60 dynes cm −2 ), which was about twice the threshold for movement of the 4 mm median diameter fine gravel bed material; and transport was almost entirely as bedload. The displacements of individual particles occurred mainly by rolling of the majority of the particles and saltation of the smallest ones, and rarely by brief sliding of large, angular ones. Entrainment was principally by rollover of the larger particles and liftoff of the smaller ones, and infrequently by ejection caused by impacts, whereas distrainment was primarily by diminution of fluid forces in the case of rolling particles and by collisions with larger bed particles in the case of saltating ones. The displacement times averaged about 0.2−0.4 s and generally were much shorter than the intervening repose times. The collective motions of the particles were characterized by frequent, brief, localized, random sweep-transport events of very high rates of entrainment and transport, which in the aggregate transported approximately 70% of the total load moved. These events occurred 9% of the time at any particular point of the bed, lasted 1–2 s, affected areas typically 20–50 cm long by 10–20 cm wide, and involved bedload concentrations approximately 10 times greater than background. The distances travelled during displacements averaged about 15 times the particle diameter. Despite the differences in their dominant modes of movement, the 8–16 mm particles typically travelled only about 30% slower during displacement than the 2–4 mm ones, whose speeds averaged 21 cm s −1 . Particles starting from the same point not only moved intermittently downstream but also dispersed both longitudinally and transversely, with diffusivities of 4.6 and 0.26 cm 2 s −1 , respectively. The bedload transport rates measured from the films were consistent with those determined conventionally with a bedload sampler. The 2–4 mm particles were entrained 6 times faster on finer areas of the bed, where 8–16 mm particles covered 6% of the surface area, than on coarser ones, where they covered 12%, even though 2–4 and 4–8 mm particles covered practically the same percentage areas in both cases. The 4–8 and 8–16 mm particles, in contrast, were entrained at the same rates in both cases. To within the statistical uncertainty, the rates of distrainment balanced the rates of entrainment for all three sizes, and were approximately proportional to the corresponding concentrations of bedload.
Triggered by the earthquake of 27 March 1964, 3 × 10 7 cubic meters of rock fell 600 meters, then slid at high speed 5 kilometers across the nearly level Sherman glacier near Cordova. The landslide has a number of significant new features in addition to those typical of other large landslides that may have slid on a layer of trapped and compressed air.
The interactions between turbulence events and sediment motions during bed load transport were studied by means of laser‐Doppler velocimetry and high‐speed cinematography. Sweeps ( u ′ > 0, w ′ < 0) which contribute positively to the mean bed shear stress, collectively move the majority of the sediment, primarily because they are extremely common. Outward interactions ( u ′ > 0 w ′ > 0) which contribute negatively to the bed shear stress and are relatively rare, individually move as much sediment as sweeps of comparable magnitude and duration, however, and much more than bursts ( u ′ < 0, w ′ > 0) and inward interactions ( u ′ < 0, w ′ < 0). When the magnitude of the outward interactions increases relative to the other events, therefore, the sediment flux increases even though the bed shear stress decreases. Thus, although bed shear stress can be used to estimate bed load transport by flows with well‐developed boundary layers, in which the flow is steady and uniform and the turbulence statistics all scale with the shear velocity, it is not accurate for flows with developing boundary layers, such as those over sufficiently nonuniform topography or roughness, in which significant spatial variations in the magnitudes and durations of the sweeps, bursts, outward interactions, and inward interactions occur. These variations produce significant peaks in bed load transport downstream of separation points, thus supporting the hypothesis that flow separation plays a significant role in the development of bed forms.
Research Article| May 01, 1985 Esker characteristics in terms of glacier physics, Katahdin esker system, Maine RONALD L. SHREVE RONALD L. SHREVE 1Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90024 Search for other works by this author on: GSW Google Scholar Author and Article Information RONALD L. SHREVE 1Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90024 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1985) 96 (5): 639–646. https://doi.org/10.1130/0016-7606(1985)96<639:ECITOG>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation RONALD L. SHREVE; Esker characteristics in terms of glacier physics, Katahdin esker system, Maine. GSA Bulletin 1985;; 96 (5): 639–646. doi: https://doi.org/10.1130/0016-7606(1985)96<639:ECITOG>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The characteristics of large, subglacially formed eskers, such as the Katahdin system, are closely related to two special peculiarities of water-filled tunnels along the beds of ice sheets: (1) the water pressure approximates the weight of the overlying ice; and (2) in tunnels that descend and those that ascend less steeply than ∼1.7 times the ice-surface gradient, the walls melt, producing a sharply arched tunnel cross section, whereas in those that ascend more steeply, they freeze, producing a wide, low one. The first peculiarity primarily governs the paths of these eskers. It causes the tunnels to follow the paths ordinary rivers would follow were the land tipped downglacier ∼11 times the local ice-surface gradient. The paths therefore trend in the general direction of the former ice flow but tend to deviate so as to follow valleys and to cross divides at the lowest passes, as observed. Ice-surface gradients calculated from path deviations at two localities on the Katahdin esker system indicate relatively thin, sluggish ice the surface of which lay ∼200 m below the summit of Mount Katahdin, in agreement with independent geologic evidence. The second peculiarity primarily governs the form, composition, and structure of these eskers. Strong melting causes a large inflow of basal ice and entrained debris to the tunnel and produces sharp-crested eskers of poorly sorted, poorly bedded sand, gravel, and boulders with lithologies like the adjacent till, whereas weaker melting produces multiple-crested ones of similar composition. Freezing precludes inflow and produces broad-crested eskers of fairly well-sorted, well-bedded, more water-worn, coarse sand with few large clasts. Ice-surface gradients calculated from transitions from the multiple-crested type to small areas of broad-crested type on the Katahdin system agree closely with those computed from the paths at nearby localities. An anomalously low gradient calculated from a transition to an area of broad-crested type approximately twice as wide and long as the probable ice depth apparently confirms that, as expected, the basal ice was supported by water pressure over most, if not all, of the width of the esker. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Research Article| September 01, 1975 The probabilistic-topologic approach to drainage-basin geomorphology Ronald L. Shreve Ronald L. Shreve 1Department of Geology and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90024 Search for other works by this author on: GSW Google Scholar Geology (1975) 3 (9): 527–529. https://doi.org/10.1130/0091-7613(1975)3<527:TPATDG>2.0.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Ronald L. Shreve; The probabilistic-topologic approach to drainage-basin geomorphology. Geology 1975;; 3 (9): 527–529. doi: https://doi.org/10.1130/0091-7613(1975)3<527:TPATDG>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyGeology Search Advanced Search Abstract Although the probabilistic-topologic approach to drainage-basin geomorphology that I initiated unifies a wide variety of quantitative empirical geomorphic relationships, some geomorphologists have objected variously that it abandons the scientific method, that its emphasis on topologic properties causes it to miss the geomorphic components of drainage basins, that it lacks physical content, and that it is too complicated to be of practical value. In fact, however, it gives results that are generally simpler, better, and more practical than those given by other methods. It has physical content because it is founded on postulates that are observational statements about actual drainage basins. It emphasizes topologic properties because they dominate the orientation-free planimetric aspects of drainage basins. Finally, it is necessarily probabilistic because of the prominent random element in natural landscapes, which may result from instabilities that amplify small perturbations into large ones. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.
There is so much common ground between studies of seasonal and perennial snow and ice that it is difficult to subdivide the broad field of glaciology (which includes all aspects of research on snow, ice, and frozen ground) in to the current AGU subcommittees of ‘Snow and Ice’ and ‘Glaciers’. A merger of the two U.S. subcommittees is now being considered. The mass balance of a glacier is the connection between the glacier's meteorological environment and its dynamic response to that environment. Heat and mass fluxes to the surface determine components of mass balances; the net mass balance at each point represents a thickening or thinning of glacier which determines changes in glacier flow. Knowledge of mass balance is crucial to any understanding of the relation of glacier dynamics to climatic variations.
Research Article| May 01, 1968 Leakage and Fluidization in Air-Layer Lubricated Avalanches RONALD L SHREVE RONALD L SHREVE Search for other works by this author on: GSW Google Scholar GSA Bulletin (1968) 79 (5): 653–658. https://doi.org/10.1130/0016-7606(1968)79[653:LAFIAL]2.0.CO;2 Article history received: 15 Mar 1967 rev-recd: 29 Apr 1967 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation RONALD L SHREVE; Leakage and Fluidization in Air-Layer Lubricated Avalanches. GSA Bulletin 1968;; 79 (5): 653–658. doi: https://doi.org/10.1130/0016-7606(1968)79[653:LAFIAL]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Air-layer lubrication, that is, nearly frictionless support on a layer of trapped and compressed air, has been suggested for the Blackhawk-type landslides and for some nuées ardentes, snow avalanches, and cratering fallback. To ensure a sufficiently small rate of air loss by leakage through a typical Blackhawk-type landslide, the harmonic mean permeability must be less than about 1 darcy, a value that is reasonable for the extremely poorly sorted debris involved. A further necessary requirement for air-layer lubrication to occur, rather than simultaneous deposition and fluidization, is that the product of the permeability and the bulk density of the basal debris be less than 0.7 times the product of the harmonic mean permeability and the arithmetic mean density for the debris as a whole, as is probably in fact the case in these landslides. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
