| 1. |
- Chandler, Benjamin M. P., et al.
(author)
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The glacial landsystem of Fjallsjökull, Iceland : Spatial and temporal evolution of process-form regimes at an active temperate glacier
- 2020
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In: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 361
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Journal article (peer-reviewed)abstract
- This study assesses the spatial and temporal evolution of the glacial landsystem signature at Fjallsjiikull, southeast Iceland, using (a) mapping of the glacial geomorphology and surficial geology and (b) repeat uncrewed aerial vehicle (UAV) surveys. A small-scale (1: 15,000 scale) landsystem map has been compiled using LiDAR data (2011-2012) and historical aerial photographs (1945-1998), along with a large-scale (1: 2000 scale) map based on UAV imagery from May 2019. From our mapping and UAV surveys, we identify sediment-landform assemblages that are typical of active temperate glacial landsystems, including recessional push/squeeze moraines and intervening flutings, overridden moraine arcs, proglacial outwash (sandur) fans and linear/ribbon sandar. We recognize three landform zones that are defined by changes in moraine morphology and the nature of proglacial outwash deposition: (1) the outer foreland is characterized by proglacial outwash fans, overridden moraine arcs and broadly linear recessional moraines; (2) the middle foreland contains sawtooth moraines and linear sandar; and (3) the innermost zone comprises extremely sawtooth and hairpin moraines as well as associated crevasse-squeeze ridge limbs. This landform zonation reflects spatio-temporal changes in moraineforming processes and outwash deposition as determined by changes in snout morphology arid proglacial drainage characteristics. Within this general tripartite zonation, we also identify localized (atonal/intrazonal) sediment-landform assemblages that are not typically found at active temperate glaciers, including ice-cored/hummocky terrain and localized kame and kettle topography. Repeat UAV surveying in 2016-2019 has allowed us to capture and quantify recent intrazonal landsystem change at the southern glacier margin. We identify a switch from moraine formation to the development of ice-cored terrain and an ice-cored esker complex in association with the uncovering of a depositional overdeepening,. Our study demonstrates the important role that variations in local boundary conditions (e.g. topography) can play in the process-form response of individual active temperate outlet glaciers, contributing to the expanding database on modern glacial landsystems.
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| 2. |
- Green, Paul F., et al.
(author)
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Thermal history solutions from thermochronology must be governed by geological relationships : A comment on Jess et al. (2019)
- 2020
-
In: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 360
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Journal article (other academic/artistic)abstract
- The recent study of the basement margin to the Nuussuaq Basin, West Greenland, by Jess et al. (2019) illustrates the problems introduced by extracting thermal histories from thermochronology data without taking into account the constraints provided by geological evidence. Their interpretations are incompatible with numerous aspects of the geology of the region, and as a result their conclusions are not valid.
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| 3. |
- Jiang, Xiangang, et al.
(author)
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Mechanism of the progressive failure of non-cohesive natural dam slopes
- 2020
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In: Geomorphology. - : ELSEVIER. - 0169-555X .- 1872-695X. ; 363
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Journal article (peer-reviewed)abstract
- Progressive failure, which begins in the downstream slopes of dams, is one of the main failure modes for natural dams in the field. However, this failure mode lacks attention in the scientific literature, especially regarding its formation mechanism. In this paper, flume tests were conducted to simulate the progressive failure of a natural dam. The results show that the progressive failure process is induced by seepage water discharging on the downstream slope, including the erosion of individual soil particles, repeated minor slip failures, upward head-cutting erosion of the dam crest, and finally the collapse of the dam when the processes have evolved sufficiently. This study focuses on analyzing the initiation mechanism of soil particle migration. The influence of seepage and interflow stresses on the incipient erosion of soil particles is analyzed. In addition, the buoyancy of soil particles on the downstream slope surface is not considered in the vertical direction in this paper but in the direction perpendicular to the downstream slope surface. The paper also discusses how to estimate the occurrence of the progressive failure of a natural dam. In the estimation method, the stress of the interfacial flow, the seepage flow stress, and the friction stress of the soil particles are considered when the phreatic line reaches the downstream slope surface.
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| 4. |
- Li, Yajun, et al.
(author)
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Distinct periods of fan aggradation and incision for tributary valleys of different sizes along the Bailong River, eastern margin of the Tibetan Plateau
- 2021
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In: Geomorphology. - : Elsevier. - 0169-555X .- 1872-695X. ; 373
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Journal article (peer-reviewed)abstract
- Understanding the mechanisms of fan incision/aggradation provides key insights into the dynamics of fan evolution and hazardous fan-forming processes. This paper focuses on the discrepancy in fan evolution for two nearby valleys of different catchment areas along the Bailong River. Specifically, we study fan evolution in the small-sized CJB valley (watershed area being 1.1 km(2)) using sedimentary analyses and C-14 dating. Sedimentary logging of seven exposed profiles indicates that mudflows and debris flows are the primary fan-forming processes. Seven samples were taken from paleosols developed in mudflow sediments, and the humin fraction was extracted for C-14 dating. These ages constrain the fan aggradation period to between 10 and 4.9 cal kyr BP, and then the incision period occurred after 4.9 cal kyr BP. As the mudflow sediments may contain organic matter from hillslope legacies, the fan aggradation period may be later than the C-14 ages defined in this study. In any case, the time of fan incision/aggradation in CJB is younger than that of the GLP valley (watershed area being 20 km(2)) where fan aggradation occurred in 21.7-7 ka and incision occurred afterward. The fan aggradation period defined by the C-14 ages in CJB is consistent with an alluvial fan of similar thickness in the southeastern Tibetan Plateau and two other fans along the Bailong River. This consistency may suggest a plausible climatic control on fan evolution for small-sized tributary valleys, while the inconsistency with the larger GLP valley may suggest different climate-response regimes for tributary valleys of different sizes. More research on similar types of alluvial fans and cross-validation of different dating methods is needed.
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| 5. |
- Lininger, Katherine B., et al.
(author)
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Evaluating floodplain organic carbon across a gradient of human alteration in the boreal zone
- 2020
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In: Geomorphology. - : Elsevier. - 0169-555X .- 1872-695X. ; 370
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Journal article (peer-reviewed)abstract
- River corridors play an important role in the carbon cycle as sites of carbon transport, storage, and transformation. Floodplain soil organic carbon (OC) and dead, downed large wood (LW) are two of the largest OC stocks in rivers. Human modifications of river corridors, such as damming and floodplain land-use change, have likely modified floodplain OC storage and retention through removal of LW and potential reduction of OC concentrations in soils. However, the effect of human alterations on floodplain OC storage is poorly understood. We measured floodplain soil OC and downed LW loads on three rivers in northern Sweden that display a gradient in the degree of human alteration. The Muddus River is located in a national park and is unaltered. The Vindel River is free-flowing but has been modified via logging and other land-use changes within the floodplain. The Ume River is dammed along its length and has also experienced floodplain logging and land-use change. We used statistical models to determine which factors are associated with differences in mineral soil OC and LW among rivers with different degrees of human alteration. We find the highest mineral soil OC concentrations on the unaltered Muddus River (mean ± standard error (SE) = 3.70 ± 0.59%; median = 3.81%), with lower soil OC along the Vindel (mean ± SE = 1.44 ± 0.22%; median = 0.72%) and Ume (mean ± SE = 2.47 ± 0.44%; median = 1.12%) Rivers. The Muddus River also has the highest downed LW loads (mean ± SE = 22.25 ± 6.99 m3 ha−1) compared to the Vindel (mean ± SE = 3.10 ± 1.26 m3 ha−1) and Ume (mean ± SE = 7.26 ± 3.53 m3 ha−1) Rivers. Variations in soil OC and downed large wood loads indicate that damming may reduce floodplain OC in these boreal systems through reducing lateral channel-floodplain connectivity and longitudinal connectivity. Logging and other land-use changes likely reduce OC inputs to the floodplain surface through removal of organic matter and LW. Further research is needed to elucidate the impact of human modifications on floodplain OC across diverse regions and to inform river restoration efforts to enhance floodplain OC storage.
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| 6. |
- Mason, Richard, et al.
(author)
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Vertical reworking of sediment by the cased caddisfly Glossosomatidae (Agapetus fuscipes) increases sand exposure and availability in armoured gravel-bed rivers
- 2022
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In: Geomorphology. - : Elsevier. - 0169-555X .- 1872-695X. ; 418
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Journal article (peer-reviewed)abstract
- Landscapes and ecosystems are the result of two-way interactions between hydro-geomorphic and biological processes. Many animals, particularly those that build structures or transport sediment, are important biogeomorphic agents. Glossosomatidae caddisfly larvae (Insecta, Trichoptera) are globally widespread and abundant inhabitants of gravel-bed rivers. Glossosomatidae build mobile cases from sand that they transport over the river bed. However, there is limited understanding on how Glossosomatidae bioconstructions may influence sand distribution in rivers or how their zoogeomorphic behaviours are influenced by hydraulics or characteristics of the river bed. First, we conducted surveys to quantify the magnitude of sand incorporated into Glossosomatidae (Agapetus fuscipes) cases within a UK river. Second, we studied A. fuscipes movement behaviour and quantified the direction and magnitude of sediment reworking, in a flume, under differing flow velocity and gravel size treatments. We found that 99 % of A. fuscipes larvae transported sediment vertically upwards. This resulted in an average conveyance per larvae of 0.06 g sand upwards by 25 mm (maximum of 50 mm). In gravel beds with a coarse surface layer, this resulted in displacement of sand from sheltered interstices onto the surface of exposed gravel particles. In the flume, this behaviour was maintained even at high flows, sufficient to entrain empty cases from these locations. Whilst the mass of sediment moved by individual larvae is small, dense populations of Glossosomatidae larvae may have important consequences for the vertical distribution of sand in rivers. At our field site, A. fuscipes case density averaged 2192 cases m- 2, equivalent to 1.4 t km-1. This finding is important because in gravel-bed rivers frequented by Glossosomatidae larvae, sediment transport is typically limited by the availability of entrainable fine grain sediment at the surface. We discuss the implications of this sediment movement for river bed sedimentary structure, the transport of sand and gravel, and the possible role of Glossosomatidae larvae as ecosystem engineers.
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| 7. |
- Meng, Jingjing, et al.
(author)
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A nodal-integration based particle finite element method (N-PFEM) to model cliff recession
- 2021
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In: Geomorphology. - : Elsevier. - 0169-555X .- 1872-695X. ; 381
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Journal article (peer-reviewed)abstract
- Cliff recession poses a significant threat to the built environment, transportation infrastructure and land use. In this paper, a novel computational framework called the Nodal-integration based Particle Finite Element Method (N-PFEM) is developed for modelling the cliff recession resulting from weathering-induced landslides. The N-PFEM combines the nodal-integration technique with the PFEM in second-order cone programming and thus requires no variable mapping operation, which is essential in the classical PFEM for modelling history-dependent materials, for modelling large deformation problems such as landslides in cliff recession processes. To verify the developed N-PFEM, a series of benchmarks have been simulated including the cliff recession under both the weathering-limited and transport-limited conditions. Simulation results from the N-PFEM are validated in detail to these from the limit analysis method, well established geomorphologic models and the discrete element method. Additionally, measures for preventing cliff recession such as the construction of retaining wall structures are also investigated using the N-PFEM.
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| 8. |
- Pérez, Lara F., et al.
(author)
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Late Quaternary sedimentary processes in the central Arctic Ocean inferred from geophysical mapping
- 2020
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In: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 369
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Journal article (peer-reviewed)abstract
- Cryospheric events in the Arctic Ocean have been largely studied through the imprints of ice sheets, ice shelves and icebergs in the seafloor morphology and sediment stratigraphy. Subglacial morphologies have been identified in the shallowest regions of the Arctic Ocean, up to 1200 m water depth, revealing the extent and dynamics of Arctic ice sheets during the last glacial periods. However, less attention has been given to sedimentary features imaged in the vicinity of the ice-grounded areas. Detailed interpretation of the sparse available swath bathymetry and sub-bottom profiles from the Lomonosov Ridge and the Amundsen Basin shows the occurrence of mass transport deposits (MTDs) and sediment waves in the central Arctic Ocean. The waxing and waning ice sheets and shelves in the Arctic Ocean have influenced the distribution of MTDs in the vicinity of grounding-ice areas, i.e. along the crest of Lomonosov Ridge. Due to the potential of Arctic sediments to hold gas hydrates, their destabilization should not be ruled out as trigger for sediment instability. Sediment waves formed by the interaction of internal waves that propagate along water mass interfaces with the bathymetric barrier of Lomonosov Ridge. This work describes the distribution and formation mechanisms of MTDs and sediment waves in the central Arctic Ocean in relation to grounding ice and internal waves between water masses, respectively. The distribution of these features provides new insight into past cryospheric and oceanographic conditions of the central Arctic Ocean.
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| 9. |
- Becher, G. P., et al.
(author)
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Sedimentology and internal structure of murtoos-V-shaped landforms indicative of a dynamic subglacial hydrological system
- 2021
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In: Geomorphology. - : Elsevier BV. - 0169-555X. ; 380:May
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Journal article (peer-reviewed)abstract
- Knowledge about processes beneath ice sheets, and in particular the processes connected to subglacial hydrology, is crucial for an understanding of ice sheets and how they react in a warming climate. Recently, v-shaped subglacial landforms (murtoos) have been found in those parts of the former Fennoscandian Ice Sheet where rapid ice-margin retreat occurred. Based on their geomorphology and distribution, murtoos have been suggested to form where the bed experienced high influxes of meltwater. Here, we investigate the sedimentology and internal structure of murtoos at four localities in southern Sweden to better understand murtoo genesis. The excavated murtoos consist of heterogenous diamict showing reasonably strong fabrics interbedded with sorted sediments. Sediments show signs of ductile deformation and lquefaction. We interpret these landforms as sub glacial landforms created by till deposition and sedimentation from meltwater with subsequent deformation. Cross-cutting relationships and inter-bedding of sorted sediments suggest a stepwise formation including periodic deformation events. We propose a model that is based on a dynamic subglacial meltwater system. We suggest that the subglacial environment is within the distributed system where the bed receives meltwater from repeated influxes of supraglacially derived meltwater. The processes suggested in this model of formation are strikingly similar to the character of glaciological and hydrological dynamics observed on the Greenland ice sheet today. ? 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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| 10. |
- Olszak, Janusz, et al.
(author)
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Post-IR IRSL dating the oldest (?) river terrace sediments in the Polish Outer Carpathians : Insights into the landscape evolution
- 2020
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In: Geomorphology. - : Elsevier BV. - 0169-555X. ; 371
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Journal article (peer-reviewed)abstract
- Post-infrared infrared stimulated luminescence (post-IR IRSL or pIRIR) was applied to determine the age of the highest-elevated alluvial sediments in the Polish Outer Carpathians. These sediments are preserved on the western slope of the Dunajec River valley, and are located 150–155 m above the present-day river channel. So far, they have been interpreted as accumulated during the Praetiglian (2.58–2.40 Ma). The pIRIR ages, however, indicate that the sediments were deposited ~2 Ma later. Such results incorporate an important record of river system evolution which has been developing very dynamically since the time of the sediment accommodation. The determined ages introduce average rate of river incision which can be calculated as 0.48–0.50 mm a−1 since the last ~309 ka. This implies that the river section has been fairly tectonically uplifting and brings attention to the rates of uplift in the rest part of the Polish Outer Carpathians. Also, adopting results from the former dating campaign, it is clear that relics of Pleistocene alluvial sediments are predominantly of cold-climate origin, and a scenario for this style of sediment preservation is proposed.
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