scholarly journals Impact of change in erosion rate and landscape steepness on hillslope and fluvial sediments grain size in the Feather River Basin (Sierra Nevada, California)

2014 ◽  
Vol 2 (2) ◽  
pp. 1047-1092 ◽  
Author(s):  
M. Attal ◽  
S. M. Mudd ◽  
M. D. Hurst ◽  
B. Weinman ◽  
K. Yoo ◽  
...  
Keyword(s):  
Grain Size ◽  
River Basin ◽  
Sierra Nevada ◽  
Sediment Flux ◽  
Fluvial Sediments ◽  
Sediment Grain Size ◽  
Erosion Rates ◽  
Wide Range ◽  
Feather River ◽  
Order Of Magnitude

Abstract. The characteristics of the sediment transported by rivers (e.g., sediment flux, grain size distribution – GSD –) dictate whether rivers aggrade or erode their substrate. They also condition the architecture and properties of sedimentary successions in basins. In this study, we investigate the relationship between landscape steepness and the grain size of hillslope and fluvial sediments. The study area is located within the Feather River Basin in Northern California, and studied basins are underlain exclusively by tonalite lithology. Erosion rates in the study area vary over an order of magnitude, from > 250 mm ka−1 in the Feather River canyon to < 15 mm ka−1 on an adjacent low relief plateau. We find that the coarseness of hillslope sediment increases with increasing hillslope steepness and erosion rates. We hypothesize that, in our soil samples, the measured ten-fold increase in D50 and doubling of the amount of fragments larger than 1 mm when slope increases from 0.38 to 0.83 m m−1 is due to a decrease in the residence time of rock fragments, causing particles to be exposed for shorter periods of time to processes that can reduce grain size. For slopes in excess of 0.7 m m−1, landslides and scree cones supply much coarser sediment to rivers, with D50 and D84 more than one order of magnitude larger than in soils. In the tributary basins of the Feather River, a prominent break in slope developed in response to the rapid incision of the Feather River. Downstream of the break in slope, fluvial sediment grain size increases, due to an increase in flow competence (mostly driven by channel steepening) but also by a change in sediment source and in sediment dynamics: on the plateau upstream of the break in slope, rivers transport easily mobilised fine-grained sediment derived exclusively from soils. Downstream of the break in slope, mass wasting processes supply a wide range of grain sizes that rivers entrain selectively, depending on the competence of their flow. Our results also suggest that in this study site, hillslopes respond rapidly to an increase in the rate of base-level lowering compared to rivers.

scholarly journals Impact of change in erosion rate and landscape steepness on hillslope and fluvial sediments grain size in the Feather River basin (Sierra Nevada, California)

2015 ◽  
Vol 3 (1) ◽  
pp. 201-222 ◽  
Author(s):  
M. Attal ◽  
S. M. Mudd ◽  
M. D. Hurst ◽  
B. Weinman ◽  
K. Yoo ◽  
...  
Keyword(s):  
Grain Size ◽  
River Basin ◽  
Sierra Nevada ◽  
Sediment Flux ◽  
Fluvial Sediments ◽  
Sediment Grain Size ◽  
Erosion Rates ◽  
Wide Range ◽  
Feather River ◽  
Order Of Magnitude

Abstract. The characteristics of the sediment transported by rivers (e.g. sediment flux, grain size distribution – GSD) dictate whether rivers aggrade or erode their substrate. They also condition the architecture and properties of sedimentary successions in basins. In this study, we investigate the relationship between landscape steepness and the grain size of hillslope and fluvial sediments. The study area is located within the Feather River basin in northern California, and studied basins are underlain exclusively by tonalite lithology. Erosion rates in the study area vary over an order of magnitude, from >250 mm ka−1 in the Feather River canyon to <15 mm ka−1 on an adjacent low-relief plateau. We find that the coarseness of hillslope sediment increases with increasing hillslope steepness and erosion rates. We hypothesise that, in our soil samples, the measured 10-fold increase in D50 and doubling of the amount of fragments larger than 1 mm when slope increases from 0.38 to 0.83 m m−1 is due to a decrease in the residence time of rock fragments, causing particles to be exposed for shorter periods of time to processes that can reduce grain size. For slopes in excess of 0.7 m m−1, landslides and scree cones supply much coarser sediment to rivers, with D50 and D84 more than one order of magnitude larger than in soils. In the tributary basins of the Feather River, a prominent break in slope developed in response to the rapid incision of the Feather River. Downstream of the break in slope, fluvial sediment grain size increases, due to an increase in flow competence (mostly driven by channel steepening) as well as a change in sediment source and in sediment dynamics: on the plateau upstream of the break in slope, rivers transport easily mobilised fine-grained sediment derived exclusively from soils. Downstream of the break in slope, mass wasting processes supply a wide range of grain sizes that rivers entrain selectively, depending on the competence of their flow. Our results also suggest that, in this study site, hillslopes respond rapidly to an increase in the rate of base-level lowering compared to rivers.

scholarly journals Universal relation with regime transition for sediment transport in fine-grained rivers

2019 ◽  
Vol 117 (1) ◽  
pp. 171-176 ◽  
Author(s):  
Hongbo Ma ◽  
Jeffrey A. Nittrouer ◽  
Baosheng Wu ◽  
Michael P. Lamb ◽  
Yuanfeng Zhang ◽  
...  
Keyword(s):  
Grain Size ◽  
Sediment Load ◽  
Yellow River ◽  
Fine Sand ◽  
Sediment Flux ◽  
Universal Relation ◽  
Sediment Grain Size ◽  
Fine Grained ◽  
Predictive Algorithm ◽  
Sediment Size

Fine-grained sediment (grain size under 2,000 μm) builds floodplains and deltas, and shapes the coastlines where much of humanity lives. However, a universal, physically based predictor of sediment flux for fine-grained rivers remains to be developed. Herein, a comprehensive sediment load database for fine-grained channels, ranging from small experimental flumes to megarivers, is used to find a predictive algorithm. Two distinct transport regimes emerge, separated by a discontinuous transition for median bed grain size within the very fine sand range (81 to 154 μm), whereby sediment flux decreases by up to 100-fold for coarser sand-bedded rivers compared to river with silt and very fine sand beds. Evidence suggests that the discontinuous change in sediment load originates from a transition of transport mode between mixed suspended bed load transport and suspension-dominated transport. Events that alter bed sediment size near the transition may significantly affect fluviocoastal morphology by drastically changing sediment flux, as shown by data from the Yellow River, China, which, over time, transitioned back and forth 3 times between states of high and low transport efficiency in response to anthropic activities.

Erosion rates and sediment flux within the Potomac River basin quantified over millennial timescales using beryllium isotopes

2019 ◽  
Vol 131 (7-8) ◽  
pp. 1295-1311 ◽  
Author(s):  
Eric W. Portenga ◽  
Paul R. Bierman ◽  
Charles D. Trodick ◽  
Sophie E. Greene ◽  
Benjamin D. DeJong ◽  
...  
Keyword(s):  
River Basin ◽  
Sediment Flux ◽  
Potomac River ◽  
Erosion Rates ◽  
Potomac River Basin ◽  
Beryllium Isotopes

scholarly journals Pervasive influence of fine silt sediments on the radiocarbon age of bulk sedimentary OC, alkenones and GDGTs via hydrodynamic mineral sorting processes in continental margins.

2020 ◽  
Author(s):  
Blanca Ausin ◽  
Elena Bruni ◽  
Negar Haghipour ◽  
Caroline Welte ◽  
Hannah Gies ◽  
...  
Keyword(s):  
Grain Size ◽  
Continental Margin ◽  
Planktonic Foraminifera ◽  
Transport Processes ◽  
Fine Silt ◽  
Sediment Grain Size ◽  
Size Fractions ◽  
Definitive Evidence ◽  
Wide Range ◽  
Grain Size Fractions

&lt;p&gt;Since Ohkouchi et al. (2002) pioneering work, compound specific radiocarbon (&lt;sup&gt;14&lt;/sup&gt;C) dating has been largely used to explore &lt;sup&gt;14&lt;/sup&gt;C age discrepancies between co-deposited sedimentary components in a wide range of depositional settings. Older &lt;sup&gt;14&lt;/sup&gt;C ages of bulk organic carbon (OC) and alkenones relative to co-deposited planktonic foraminifera have been mainly attributed to lateral sediment transport processes by means of organic matter (OM)-mineral associations.&lt;/p&gt;&lt;p&gt;Definitive evidence for this hypothesis requires in-depth investigations at the mineral grain-size level. Here, we examine the radiocarbon signatures of OC and two molecular biomarkers widely used as paleothermometers (i.e., alkenones and glycerol diakyl glycerol tetraether (GDGTs)) associated to discrete sediment grain-size fractions collected from a range of continental margin settings. Our results evidence the pervasive influence of hydrodynamically-driven sorting processes on the OM content and composition of continental margin sediments, manifested in the &lt;sup&gt;14&lt;/sup&gt;C age variability of OC, alkenones and GDGTs residing in bulk sediments corresponding grain-size fractions. We find that OC and both, alkenones and GDGTs, preferentially reside within the fine silt fraction, which accounts for a substantial fraction of the bulk sediment mass. Therefore, fine silt exerts a strong influence on the &lt;sup&gt;14&lt;/sup&gt;C ages of these three components in bulk sediments. Given the propensity to resuspension and advection of fine silt under strong currents, the extent of its impact on the paleotemperature signal recorded by alkenones and GDGTs is also assessed.&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Ohkouchi, N., Eglinton, T.I., Keigwin, L.D., Hayes, J.M., 2002. Spatial and Temporal Offsets Between Proxy Records in a Sediment Drift. Science 298, 1224-1227.&lt;/p&gt;

Examining erosion in New Zealand over millennial timescales using in-situ 10Be and 14C

2020 ◽  
Author(s):  
Duna Roda-Boluda ◽  
Taylor Schilgen ◽  
Maarten Lupker ◽  
Wittmann Hella ◽  
Prancevic Jeff ◽  
...  
Keyword(s):  
New Zealand ◽  
Erosion Rate ◽  
Sediment Flux ◽  
Short Term ◽  
Sediment Fluxes ◽  
Landslide Activity ◽  
Erosion Rates ◽  
Order Of Magnitude

&lt;p&gt;Landslides are the major erosional process in many orogens, and one of the most sensitive erosional process to tectonic and climatic perturbations. However, it remains extremely difficult to constrain long-term or past rates of landslide activity, and hence their contribution to long-term landscape evolution and catchment sediment fluxes, because the physical records of landsliding are often removed in &lt;10&lt;sup&gt;2&lt;/sup&gt; yrs. Here, we use the in-situ &lt;sup&gt;10&lt;/sup&gt;Be and in-situ &lt;sup&gt;14&lt;/sup&gt;C concentrations of recent landslide deposits and catchments from the Fiordland and the Southern Alps of New Zealand to: (a) estimate landslide frequencies over 10&lt;sup&gt;3&lt;/sup&gt;-10&lt;sup&gt;4&lt;/sup&gt; yr timescales, which we compare against landslide inventories mapped from air photos (&lt;10&lt;sup&gt;2&lt;/sup&gt; yrs) to estimate changes in landslide activity, (b) quantify catchment-averaged erosion rates, and landslide&amp;#8217;s contribution to those erosional fluxes, and (c) test whether paired &lt;sup&gt;14&lt;/sup&gt;C-&lt;sup&gt;10&lt;/sup&gt;Be measurements can be used to trace erosional depth-provenance and identify transient erosion rate changes. We show that &lt;sup&gt;10&lt;/sup&gt;Be concentrations on landslide deposits can be used to estimate landslide recurrence intervals and frequency over 10&lt;sup&gt;3&lt;/sup&gt; yr timescales, and that &lt;sup&gt;14&lt;/sup&gt;C/&lt;sup&gt;10&lt;/sup&gt;Be ratios reflect the depth-provenance of sediment, and possibly transient changes in erosion rates. The comparison of our &lt;sup&gt;10&lt;/sup&gt;Be-based long-term landslide frequencies with short-term published inventories suggests that landslide frequencies have increased towards the present by up to an order of magnitude. We compare sediment fluxes inferred from these long- and short-term landslide inventories with sediment flux estimates derived from &lt;sup&gt;10&lt;/sup&gt;Be catchment-averaged erosion rates, which allows us to examine fluctuations in erosion rate estimates from 10&lt;sup&gt;1&lt;/sup&gt; to 10&lt;sup&gt;3&lt;/sup&gt; yrs timescales.&amp;#160;&lt;/p&gt;

scholarly journals Comparative organic geochemistry of Indian margin (Arabian Sea) sediments: estuary to continental slope

2014 ◽  
Vol 11 (23) ◽  
pp. 6683-6696 ◽  
Author(s):  
G. Cowie ◽  
S. Mowbray ◽  
S. Kurian ◽  
A. Sarkar ◽  
C. White ◽  
...  
Keyword(s):  
Grain Size ◽  
Continental Slope ◽  
Arabian Sea ◽  
Sediment Surface ◽  
Sediment Grain Size ◽  
Organic C ◽  
Shelf Sediment ◽  
Wide Range ◽  
Hydrodynamic Processes ◽  
Upper Slope

Abstract. Surface sediments from sites across the Indian margin of the Arabian Sea were analysed for their elemental and stable isotopic organic carbon (Corg) and total nitrogen compositions, grain size distributions and biochemical indices of organic matter (OM) source and/or degradation state. Site locations ranged from the estuaries of the Mandovi and Zuari rivers to depths of ~ 2000 m on the continental slope, thus spanning nearshore muds and sands on the shelf and both the oxygen minimum zone (OMZ) on the upper slope (~ 200–1300 m) and the seasonal hypoxic zone that appears on the shelf. Source indices showed mixed marine and terrigenous OM within the estuaries, but consistent predominance (80–100%) of marine OM on the shelf and slope. Thus, riverine terrigenous OM is diluted or replaced by autochthonous marine OM and/or is efficiently re-mineralised, within or immediately offshore of the estuaries. Organic C contents of surface shelf sediments varied from < 0.5 wt% in relict shelf sands to up to ~ 4 wt% for nearshore muds, while upper slope sites within the OMZ showed a wide range (~ 2 to 7 + wt%), progressively decreasing below the OMZ to ≤ 1 wt% at 2000 m. Thus, major variability (~ 5 wt%) was found at slope sites within the OMZ of similar depth and near-identical bottom-water O2 concentrations. A strong relationship between %Corg and sediment grain size was seen for sediments within the OMZ, but lower relative Corg contents were found for sites on the shelf and below the OMZ. Further, Corg loadings, when related to estimated sediment surface area, indicated distinct enrichment of Corg in the OMZ sediments relative to sites above and below the OMZ and to sediments from normoxic margins. Diagenetic indices confirmed that lower Corg content below the OMZ is associated with more extensive OM degradation, but that shelf sediment OM is not consistently more degraded than that found within the OMZ. Together, the results indicate that OM distribution across the margin is controlled by interplay between hydrodynamic processes and varying preservation associated with O2 availability. This inference is supported by multiple regression analysis. Hydrodynamic processes (expressed as %Silt) followed by O2 availability, can explain the large majority of %Corg variability when the shelf and slope are considered as a whole. However, while O2 becomes the primary influence on %Corg for sediments below the OMZ, %Silt is the primary influence across the OMZ and, apparently, the shelf. Thus, reduced O2 exposure is responsible for OM enrichment within the OMZ, but hydrodynamic processes are the overriding control on sediment OM distributions across both the shelf and the OMZ.

Climatic/Hydrologic Oscillations since 155,000 yr B.P. at Owens Lake, California, Reflected in Abundance and Stable Isotope Composition of Sediment Carbonate

1997 ◽  
Vol 48 (1) ◽  
pp. 58-68 ◽  
Author(s):  
Kirsten M. Menking ◽  
James L. Bischoff ◽  
John A. Fitzpatrick ◽  
James W. Burdette ◽  
Robert O. Rye
Keyword(s):  
Climate Change ◽  
Grain Size ◽  
Sierra Nevada ◽  
Isotope Composition ◽  
Carbonate Content ◽  
Stable Isotope Composition ◽  
Sediment Grain Size ◽  
First Order ◽  
Owens Lake ◽  
Isotopic Records

Sediment grain size, carbonate content, and stable isotopes in 70-cm-long (∼1500-yr) channel samples from Owens Lake core OL-92 record many oscillations representing climate change in the eastern Sierra Nevada region since 155,000 yr B.P. To first order, the records match well the marine δ18O record. At Owens Lake, however, the last interglaciation appears to span the entire period from 120,000 to 50,000 yr B.P., according to our chronology, and was punctuated by numerous short periods of wetter conditions during an otherwise dry climate. Sediment proxies reveal that the apparent timing of glacial–interglacial transitions, notably the penultimate one, is proxy-dependent. In the grain-size and carbonate-content records this transition is abrupt and occurs at ∼120,000 yr B.P. In contrast, in the isotopic records the transition is gradual and occurs between 145,000 and 120,000 yr B.P. Differences in timing of the transition are attributed to variable responses by proxies to climate change.

Novel magneto-optical recording materials: Bi-substituted garnet films

1991 ◽  
Vol 49 ◽  
pp. 776-777
Author(s):  
Takao Suzuki ◽  
Hossein Nuri
Keyword(s):  
Grain Size ◽  
Amorphous Film ◽  
Nitrogen Atmosphere ◽  
Optical Recording ◽  
Garnet Film ◽  
Media Noise ◽  
Garnet Films ◽  
Order Of Magnitude ◽  
A New Technique ◽  
A Current

For future high density magneto-optical recording materials, a Bi-substituted garnet film ((BiDy)3(FeGa)5O12) is an attractive candidate since it has strong magneto-optic effect at short wavelengths less than 600 nm. The signal in read back performance at 500 nm using a garnet film can be an order of magnitude higher than a current rare earth-transition metal amorphous film. However, the granularity and surface roughness of such crystalline garnet films are the key to control for minimizing media noise.We have demonstrated a new technique to fabricate a garnet film which has much smaller grain size and smoother surfaces than those annealed in a conventional oven. This method employs a high ramp-up rate annealing (Γ = 50 ~ 100 C/s) in nitrogen atmosphere. Fig.1 shows a typical microstruture of a Bi-susbtituted garnet film deposited by r.f. sputtering and then subsequently crystallized by a rapid thermal annealing technique at Γ = 50 C/s at 650 °C for 2 min. The structure is a single phase of garnet, and a grain size is about 300A.

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