1,720,985 research outputs found
Reconstruction of North American Drainage Basins and River Discharge Since the Last Glacial Maximum
No full textChanges in major drainage basins and river discharges across North American since the Last Glacial Maximum from calculations based on five different reconstructions of past ice sheets and glacial-isostatic adjustment. River discharges are stored as Numpy binary files. Drainage basins are stored as shapefiles. Images and videos are available for each ice-sheet and glaical-isostatic adjustment model tested. These images show past topography and sea level, drainage basin extents as black lines, rivers with local flow greater than 1000 cubic meters per second as blue lines, and the footprint of the ice-sheet as a semitransparent light-colored region. Ages are in the folder and file names for the drainage basins and the images, and take the form, "0XXXXX', where this is the number of years before present (i.e. before 1950) that the rivers of North America are simulated to be structured as shown.Drainage basins and river discharges since the Last Glacial Maximum; released along with the article "Reconstruction of North American drainage basins and river discharge since the Last Glacial Maximum" to appear in the journal "Earth Surface Dynamics".National Defense Science & Engineering Graduate Fellowship ProgramNational Science Foundation Graduate Research Fellowship under Grant No. DGE 1144083Emmy Noether Programme of the Deutsche Forschungsgemeinschaft (DFG) through funds awarded to T. Schildgen under Grant No. SCHI 1241/1-1Start-up funds from the University of MinnesotaWickert, Andrew D. (2016). Reconstruction of North American Drainage Basins and River Discharge Since the Last Glacial Maximum. Retrieved from the University Digital Conservancy, http://doi.org/10.13020/D6D01H
Experimental alluvial-river and landsliding response to base-level fall
No full textAll files with time-dependent data contain 7-digit time stamps that provide the number of seconds since the start of each experiment.
(1) Georeferenced overhead photos in GeoTIFF format within a Tape ARchive (tar).
(2) Digital elevation models in GeoTIFF format within a GZipped Tape ARchive (tar.gz).
(3) Landslide GIS vector areas (polygons) organized by experiment and time as ESRI Shapefiles stored within a GZipped Tape ARchive (tar.gz). Each subfolder is labeled .shx (the ".shx" is spurious) and contains the shp, shx, dbf, and prj files associated with each set of landslides at each time in the experiment.
(4) Landslide attributes as comma-separated variables (csv) files for each experiments, stored within an XZipped Tape ARchive (tar.xz). Each CSV includes (in order): the x and y positions of the landslide center, the width (y-directed – i.e., cross-valley – distance from one end to the other) and length (x-directed – i.e., down-valley – distance from one end to the other) of the landslide, mean landslide depth, landslide area measured in the x-y (i.e., horizontal) plane, the semi-major and semi-minor axes of an ellipse fit to the landslide, the angle from the semi-major axis to the "horizontal" (confusingly meaning the x orientation, since I was thinking in x-y space while writing the analysis code), landslide volume calculated by subtracting the valley-bottom elevation from that of the DEM surface in the landslide area, the runtime at which the landslide occurs, and the wait time between landslide events.
(5) Movies at 15 fps (5 minutes experiment time per 1 second watch time) for the full series of images from each experiment, stored within an XZipped Tape ARchive (tar.xz). I did not adjust for occasional skipped images (e.g., around the time of the laser scans), which will cause minor deviations from the 5-minutes-runtime-to-1-second-video conversion.
(6) Schematic image (png) of a georeferenced overhead photo (ImgSec_0043168) atop a shaded-relief map (DEM_fullextent_0043188) with hatched landslide locations from runtimes after 0043168. Shadows running along the x axis show zones near the outlet where the basin walls prevented the angled laser-topography scanner from casting light on the the valley bottom. All images are from the 25 mm/hr base-level fall experiment.We observed the incisional response of an alluvial river to base-level fall. We conducted the experiment in a 3.9 × 2.4 × 0.4 m box that we filled with uniform 0.140±0.04 mm sand. We dropped base level by lowering the elevation of an "ocean" pool at the river outlet. As the initial condition, we cut a 10±2 cm wide channel to a steadily increasing depth, from 3±0.5 cm at the inlet, where we supplied water and sediment, to 10±1 cm at the outlet. Input water and sediment discharge were 0.1 L/s and 0.0022 L/s (including pore space), respectively. As base level fell, the river incised and migrated laterally, forming a valley with abandoned terrace surfaces and walls that failed in mass-wasting events as they were undercut. We include a control case with no base-level fall, as well as experiments with 25 mm/hr, 50 mm/hr, 200 mm/hr, 300 mm/hr, and 400 mm/hr of base-level fall. We supply georeferenced overhead photos (0.89 mm resolution, every 20 seconds), digital elevation models (DEMs, 1 mm horizontal resolution, every 15–30 minutes), videos generated from the overhead photos, mapped landslides in GIS vector area (polygon) format, and landslide attributes. Relevant code to process and plot the data, as well as further information on grain size, is available from GitHub and Zenodo.Start-up funds to A. Wickert from the University of MinnesotaRichard C. Dennis Fellowship awarded by the Department of Earth Sciences to O. BeaulieuBeaulieu, Olivia P; Wickert, Andrew D; Witte, Elizabeth D; Tofelde, Stefanie. (2020). Experimental alluvial-river and landsliding response to base-level fall. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/zw6r-am46
100 kyr fluvial cut-and-fill terrace cycles since the Middle Pleistocene in the southern Central Andes, NW Argentina
No full textFluvial fill terraces in intermontane basins are valuable geomorphic archives that can record tectonically and/or climatically driven changes of the Earth-surface process system. However, often the preservation of fill terrace sequences is incomplete and/or they may form far away from their source areas, complicating the identification of causal links between forcing mechanisms and landscape response, especially over multi-millennial timescales. The intermontane Toro Basin in the southern Central Andes exhibits at least five generations of fluvial terraces that have been sculpted into several-hundred-meter-thick Quaternary valley-fill conglomerates. New surface-exposure dating using nine cosmogenic 10Be depth profiles reveals the successive abandonment of these terraces with a 100 kyr cyclicity between 75±7 and 487±34 ka. Depositional ages of the conglomerates, determined by four 26Al/10Be burial samples and U–Pb zircon ages of three intercalated volcanic ash beds, range from 18±141 to 936±170 ka, indicating that there were multiple cut-and-fill episodes. Although the initial onset of aggradation at ∼1 Ma and the overall net incision since ca. 500 ka can be linked to tectonic processes at the narrow basin outlet, the superimposed 100 kyr cycles of aggradation and incision are best explained by eccentricity-driven climate change. Within these cycles, the onset of river incision can be correlated with global cold periods and enhanced humid phases recorded in paleoclimate archives on the adjacent Bolivian Altiplano, whereas deposition occurred mainly during more arid phases on the Altiplano and global interglacial periods. We suggest that enhanced runoff during global cold phases – due to increased regional precipitation rates, reduced evapotranspiration, or both – resulted in an increased sediment-transport capacity in the Toro Basin, which outweighed any possible increases in upstream sediment supply and thus triggered incision. Compared with two nearby basins that record precessional (21-kyr) and long-eccentricity (400-kyr) forcing within sedimentary and geomorphic archives, the recorded cyclicity scales with the square of the drainage basin length.Fil: Tofelde, Stefanie. Universitat Potsdam; Alemania. Deutsches Geo Forschungs Zentrum; AlemaniaFil: Schildgen, Taylor F.. Universitat Potsdam; Alemania. Deutsches Geo Forschungs Zentrum; AlemaniaFil: Savi, Sara. Universitat Potsdam; AlemaniaFil: Pingel, Heiko. Universitat Potsdam; AlemaniaFil: Wickert, Andrew D.. University of Minnesota; Estados UnidosFil: Bookhagen, Bodo. Universitat Potsdam; AlemaniaFil: Wittmann, Hella. Deutsches Geo Forschungs Zentrum; AlemaniaFil: Alonso, Ricardo Narciso. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; ArgentinaFil: Cottle, John. University of California; Estados UnidosFil: Strecker, Manfred R.. Universitat Potsdam; Alemani
Alluvial channel response to environmental perturbations: fill-terrace formation and sediment-signal disruption
No full textThe sensitivity of fluvial systems to tectonic and climatic boundary conditions allows us to use the geomorphic and stratigraphic records as quantitative archives of past climatic and tectonic conditions. Thus, fluvial terraces that form on alluvial fans and floodplains as well as the rate of sediment export to oceanic and continental basins are commonly used to reconstruct paleoenvironments. However, we currently lack a systematic and quantitative understanding of the transient evolution of fluvial systems and their associated sediment storage and release in response to changes in base level, water input, and sediment input. Such knowledge is necessary to quantify past environmental change from terrace records or sedimentary deposits and to disentangle the multiple possible causes for terrace formation and sediment deposition. Here, we use a set of seven physical experiments to explore terrace formation and sediment export from a single, braided channel that is perturbed by changes in upstream water discharge or sediment supply, or through downstream base-level fall. Each perturbation differently affects (1) the geometry of terraces and channels, (2) the timing of terrace cutting, and (3) the transient response of sediment export from the basin. In general, an increase in water discharge leads to near-instantaneous channel incision across the entire fluvial system and consequent local terrace cutting, thus preserving the initial channel slope on terrace surfaces, and it also produces a transient increase in sediment export from the system. In contrast, a decreased upstream sediment-supply rate may result in longer lag times before terrace cutting, leading to terrace slopes that differ from the initial channel slope, and also lagged responses in sediment export. Finally, downstream base-level fall triggers the upstream propagation of a diffuse knickzone, forming terraces with upstream-decreasing ages. The slope of terraces triggered by base-level fall mimics that of the newly adjusted active channel, whereas slopes of terraces triggered by a decrease in upstream sediment discharge or an increase in upstream water discharge are steeper compared to the new equilibrium channel. By combining fill-terrace records with constraints on sediment export, we can distinguish among environmental perturbations that would otherwise remain unresolved when using just one of these records
Interactions between main channels and tributary alluvial fans: channel adjustments and sediment-signal propagation
No full textClimate and tectonics impact water and sediment fluxes to fluvial systems. These boundary conditions set river form and can be recorded by fluvial deposits. Reconstructions of boundary conditions from these deposits, however, is complicated by complex channel-network interactions and associated sediment storage and release through the fluvial system. To address this challenge, we used a physical experiment to study the interplay between a main channel and a tributary under different forcing conditions. In particular, we investigated the impact of a single tributary junction, where sediment supply from the tributary can produce an alluvial fan, on channel geometries and associated sediment-transfer dynamics. We found that the presence of an alluvial fan may either promote or prevent the movement of sediment within the fluvial system, creating different coupling conditions. By analyzing different environmental scenarios, our results reveal the contribution of both the main channel and the tributary to fluvial deposits upstream and downstream from the tributary junction. We summarize all findings in a new conceptual framework that illustrates the possible interactions between tributary alluvial fans and a main channel under different environmental conditions. This framework provides a better understanding of the composition and architecture of fluvial sedimentary deposits found at confluence zones, which can facilitate the reconstruction of the climatic or tectonic history of a basin
NorthernWidget/SetTime_GUI: Version 1.0.0
No full text<p>Stable release to accompany the HESS Discussions paper</p>
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Glacial isostatic uplift of the European Alps
Full text linkFollowing the last glacial maximum (LGM), the demise of continental ice sheets induced crustal rebound in tectonically stable regions of North America and Scandinavia that is still ongoing. Unlike the ice sheets, the Alpine ice cap developed in an orogen where the measured uplift is potentially attributed to tectonic shortening, lithospheric delamination and unloading due to deglaciation and erosion. Here we show that ∼90% of the geodetically measured rock uplift in the Alps can be explained by the Earth's viscoelastic response to LGM deglaciation. We modelled rock uplift by reconstructing the Alpine ice cap, while accounting for postglacial erosion, sediment deposition and spatial variations in lithospheric rigidity. Clusters of excessive uplift in the Rhône Valley and in the Eastern Alps delineate regions potentially affected by mantle processes, crustal heterogeneity and active tectonics. Our study shows that even small LGM ice caps can dominate present-day rock uplift in tectonically active regions
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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