ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    facet.materialart.
    Unknown
    Lamb Receives 2012 Luna B. Leopold Young Scientist Award: Response (2013)
    Wiley
    Details
    Publication Date: 2013-09-18
    Description: It is my pleasure to be a part of the exciting community of Earth and planetary surface processes. In addition to the opportunities to participate in engaging and fundamental science, I enjoy our field because of collaborations with bright and fun people. In my short career I have had the pleasure to work with a number of colleagues, and I share this award with you.
    Print ISSN: 0096-3941
    Electronic ISSN: 2324-9250
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 2
    facet.materialart.
    Unknown
    Influence of bed patchiness, slope, grain hiding, and form drag on gravel mobilization in very steep streams (2013)
    Wiley
    Details
    Publication Date: 2013-04-03
    Description: [1]  Steep streams are a major portion of channel networks and provide a link to transport sediment from hillslopes to lower gradient rivers. Despite their importance, key unknowns remain, perhaps foremost of which is evaluating in steep streams empirical laws for fluvial sediment transport developed for low-gradient rivers. To address this knowledge gap, we painted sediment in situ over three years to monitor incipient sediment motion and sediment patch development in five small (drainage areas of 0.04–2 km 2 ) and steep (slopes of 5 – 37%) tributaries of Elder Creek, California, USA. We found that channel beds organized into size-sorted sediment patches which displayed active fluvial transport of gravel annually, consistent year-to-year patch median-grain sizes, partial transport of bed material, and significantly higher values of critical Shields stress for incipient sediment motion compared to that observed for lower gradient rivers. The high critical Shields stresses (up to 0.5 for the median grain size) agree within a factor of ~3 to theoretical predictions which account for slope-dependent hydraulics, grain hiding, and sediment patches. For grains of approximately the same size as the roughness length scale, slope-dependent hydraulics and bed patchiness are the dominant controls on critical Shields stress values, while grain hiding is important for grains larger or smaller than the roughness length scale. Form drag exists in our monitored tributaries, but has a smaller influence than the above effects. Our field observations show fluvial processes contribute to sediment mobilization in steep channels which are often considered to be dominated by debris flows.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 3
    facet.materialart.
    Unknown
    Hydraulics of floods upstream of horseshoe canyons and waterfalls (2015)
    Wiley
    Details
    Publication Date: 2015-05-15
    Description: Horseshoe waterfalls are ubiquitous in natural streams, bedrock canyons, and engineering structures. Nevertheless, water flow patterns upstream of horseshoe waterfalls are poorly known, and likely differ from the better studied case of a one-dimensional linear step because of flow focusing into the horseshoe. This is a significant knowledge gap because the hydraulics at waterfalls controls sediment transport and bedrock incision, which can compromise the integrity of engineered structures and influence the evolution of river canyons on Earth and Mars. Here we develop new semi-empirical theory for the spatial acceleration of water upstream of, and the cumulative discharge into, horseshoe canyons and waterfalls. To this end, we performed 110 numerical experiments by solving the 2-D depth-averaged shallow water equations for a wide range of flood depths, widths and discharges, and canyon lengths, widths and bed gradients. We show that the upstream, normal-flow Froude number is the dominant control on lateral flow focusing and acceleration into the canyon head, and that focusing is limited when the flood-width is small compared to a cross-stream backwater length scale. In addition, for sheet floods much wider than the canyon, flow focusing into the canyon head leads to reduced discharge (and drying in cases) across the canyon side-walls, which is especially pronounced for canyons that are much longer than they are wide. Our results provide new expectations for morphodynamic feedbacks between floods and topography, and thus canyon formation.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 4
    facet.materialart.
    Unknown
    Self-formed bedrock waterfalls (2019)
    Springer Nature
    In: Nature
    Details
    Publication Date: 2019
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 5
    facet.materialart.
    Unknown
    Canyon formation constraints on the discharge of catastrophic outburst floods of Earth and Mars (2016)
    Wiley
    Details
    Publication Date: 2016-06-15
    Description: Catastrophic outburst floods carved amphitheater-headed canyons on Earth and Mars, and the steep headwalls of these canyons suggest that some formed by upstream headwall propagation through waterfall erosion processes. Because topography evolves in concert with water flow during canyon erosion, we suggest that bedrock canyon morphology preserves hydraulic information about canyon-forming floods. In particular, we propose that for a canyon to form with a roughly uniform width by upstream headwall retreat, erosion must occur around the canyon head, but not along the sidewalls, such that canyon width is related to flood discharge. We develop a new theory for bedrock canyon formation by megafloods based on flow convergence of large outburst floods towards a horseshoe-shaped waterfall. The model is developed for waterfall erosion by rock toppling, a candidate erosion mechanism in well-fractured rock, like columnar basalt. We apply the model to fourteen terrestrial (Channeled Scablands, Washington; Snake River Plain, Idaho; Ásbyrgi Canyon, Iceland) and nine martian (near Ares Vallis and Echus Chasma) bedrock canyons, and show that predicted flood discharges are nearly three orders of magnitude less than previously estimated, and predicted flood durations are longer than previously estimated, from less than a day to a few months. Results also show a positive correlation between flood discharge per unit width and canyon width, which supports our hypothesis that canyon width is set in part by flood discharge. Despite lower discharges than previously estimated, the flood volumes remain large enough for individual outburst floods to have perturbed the global hydrology of Mars.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 6
    facet.materialart.
    Unknown
    Avulsion cycles and their stratigraphic signature on an experimental backwater-controlled delta (2016)
    Wiley
    Details
    Publication Date: 2016-08-18
    Description: River deltas grow in large part through repeated cycles of lobe construction and channel avulsion. Understanding avulsion cycles is important for coastal restoration and ecology, land management, and flood hazard mitigation. Emerging theories suggest that river avulsions on lowland deltas are controlled by backwater hydrodynamics; however, our knowledge of backwater-controlled avulsion cycles is limited. Here, we present results from an experimental delta that evolved under persistent backwater hydrodynamics achieved through variable flood discharges, shallow bed-slopes, and subcritical flows. The experimental avulsion cycles consisted of an initial phase of avulsion setup, an avulsion trigger, selection of a new flow path, and abandonment of the parent channel. Avulsions were triggered during the largest floods (78% of avulsions) after the channel was filled by a fraction (0.3 ± 0.13) of its characteristic flow depth at the avulsion site, which occurred in the upstream part of the backwater zone. The new flow path following avulsion was consistently one of the shortest paths to the shoreline, and channel abandonment occurred through temporal decline in water flow and sediment delivery to the parent channel. Experimental synthetic stratigraphy indicates that the bed thicknesses were maximum at the avulsion sites, consistent with our morphologic measurements of avulsion setup and the idea that there is a record of avulsion locations and thresholds in sedimentary rocks. Finally, we discuss the implications of our findings within the context of sustainable management of deltas, their stratigraphic record, and predicting avulsions on deltas.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 7
    facet.materialart.
    Unknown
    Structure of turbulence and sediment stratification in wave-supported mud layers (2015)
    Wiley
    Details
    Publication Date: 2015-02-19
    Description: We present results from laboratory experiments in a wave flume with and without a sediment bed to investigate the turbulent structure and sediment dynamics of wave-supported mud layers. The presence of sediment on the bed significantly alters the structure of the wave boundary layer relative to that observed in the absence of sediment, increasing the TKE by more than a factor of three at low wave orbital velocities and suppressing it at the highest velocities. The transition between the low and high velocity regimes occurs when Re ∆ ≃ 450, where Re ∆ is the Stokes Reynolds number. In the low velocity regime ( Re ∆ 〈 450) the flow is significantly influenced by the formation of ripples, which enhances the TKE and Reynolds stress, and increases the wave boundary layer thickness. In the high velocity regime ( Re ∆ 〉 450) the ripples are significantly smaller, the near-bed sediment concentrations are significantly higher and density stratification due to sediment becomes important. In this regime the TKE and Reynolds stress are lower in the sediment bed runs than in comparable runs with no sediment. The regime transition at Re ∆ = 450 appears to result from washout of the ripples and increased concentrations of fine sand suspended in the boundary layer, which increases the settling flux and the stratification near the bed. The increased stratification damps turbulence, especially near the top of the high concentration layer, reducing the layer thickness. We anticipate that these effects will influence the transport capacity of wave-supported gravity currents on the continental shelf. This article is protected by copyright. All rights reserved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 8
    facet.materialart.
    Unknown
    Vegetation and wildfire controls on sediment yield in bedrock landscapes (2013)
    Wiley
    Details
    Publication Date: 2013-02-26
    Description: [1]  Steep, rocky landscapes commonly exhibit high sediment yields and are especially sensitive to climate, tectonics, and wildfire. Predicting landscape response to these perturbations demands a quantitative understanding of erosion processes. However, existing models for hillslope sediment production and transport do not apply to landscapes with patchy soil and slopes that exceed the angle for sediment stability. Here we present field measurements in southern California, USA, which indicate that sediment storage on steep slopes is enabled by vegetation that traps sediment upslope. We find that the storage capacity of unburned vegetation dams follows a geometric scaling model with a cubic dependence on effective plant width and an inverse dependence on local slope. Measuredsediment volumes behind burned vegetation dams indicate a loss of at least75% relative to unburned dams, and when expanded to the catchment scale, our measurements match records of post-fire sediment yield from nearby retention basins. Contrary to existing models, our observations indicate that wildfire-induced sediment yield is driven by transient storage and release of sediment by vegetation dams, rather than increasedbedrock-to-soil conversion rates. Without a feedback between soil production and wildfire, fire may play little role in long-term landscape evolution, and increasing fire frequency in response to climate change may not result in heightened sedimentation hazards due to supply limitations.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 9
    facet.materialart.
    Unknown
    Deciphering boulder mobility and erosion from cosmogenic nuclide exposure dating (2013)
    Wiley
    Details
    Publication Date: 2013-02-05
    Description: [1]  Large boulders are prominent features in many geomorphic systems, and are frequently targeted for cosmogenic exposure dating. Presently, there is little data or theory predicting exposure age, erosion rate and mobilization frequency of boulders in environments such as channels, talus slopes, or moraines. Here we explore the potential for cosmogenic isotope analysis to constrain the transport and erosion history of boulders. Through a series of numerical experiments we model the statistical evolution of nuclide concentrations around the surface of boulders. Stable boulders have distinctive radial distributions of surface concentration in comparison to those that are periodically mobile, and this can be used to establish boulder stability. Mean nuclide accumulation rates around the surface of an eroding boulder increase when the radius is smaller than approximately 1.5 e-folding lengths (~1.2 m) of neutron flux intensity, whereupon nuclide accumulation on the underside of the boulder becomes non-negligible (~10%). Model results for cases of no cosmogenic inheritance and uniform erosion indicate the normalized standard deviation of nuclide surface concentration systematically decreases with increasing number of boulder mobilization events. This may be used to constrain the minimum number of times a boulder has moved for up to ~4 events, or distinguish between rarely and frequently mobilized boulders. Using non-dimensional scaling relations between surface concentration statistics, boulder size, and time, we propose methods to estimate the minimum age, frequency of movement, and erosion rate of mobile boulders with application to a range of geomorphic problems.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 10
    facet.materialart.
    Unknown
    A model for fire-induced sediment yield by dry ravel in steep landscapes (2011)
    Wiley
    Details
    Publication Date: 2011-07-29
    Description: Sediment flux from hillslopes to channels commonly increases following wildfires, with implications for the carbon cycle, river habitats, and debris-flow hazards. Although much of this material is transported via dry ravel, existing ravel models are not applicable to hillslopes with gradients greater than the angle of repose, which can constitute the majority of mountainous terrain. To fill this knowledge gap, we develop a continuity model for sediment storage by vegetation dams on steep hillslopes to predict sediment yields following wildfire. The maximum volume of sediment stored prior to wildfire is set to be a function of vegetation density, the capacity of plants to impound sediment, and the contributing hillslope area. Time is required after fire to establish vegetation and replenish hillslope sediment storage, which introduces vegetation regrowth rate, soil production rate, and fire recurrence interval as important variables that affect ravel yield. Model results for the San Gabriel Mountains, California, predict that sediment yield can increase by several orders of magnitude following fire. These results are consistent with field data of ravel yield (∼30 mm per contributing area of hillslope in 5 months) we collected following the 2009 Station Fire, as well as postfire sediment flux recorded by 93 debris basins. In contrast to previous work, our model shows that heightened postfire sediment yields can be explained by a change in hillslope sediment storage independent of major changes in the soil production rate and landscape form over geomorphic timescales.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...