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  • 1
    Publication Date: 2011-03-16
    Description: The northwest Argentine Andes constitute a premier natural laboratory to assess the complex interactions between isolated uplifts, orographic precipitation gradients, and related erosion and sedimentation patterns. Here we present new stratigraphic observations and age information from intermontane basin sediments to elucidate the Neogene to Quaternary shortening history and associated sediment dynamics of the broken Salta foreland. This part of the Andean orogen, which comprises an array of basement-cored range uplifts, is located at ∼25°S and lies to the east of the arid intraorogenic Altiplano/Puna plateau. In the Salta foreland, spatially and temporally disparate range uplift along steeply dipping inherited faults has resulted in foreland compartmentalization with steep basin-to-basin precipitation gradients. Sediment architecture and facies associations record a three-phase (∼10, ∼5, and
    Print ISSN: 0278-7407
    Electronic ISSN: 1944-9194
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Publication Date: 2014-01-14
    Description: [1]  We examine the relationship of channel steepness to incision rate from channels eroding into a previously tilted, planar, and progressively exhumed unconformity surface cut across erosionally resistant limestone bedrock. Key to this analysis is the calibrated substitution of down-slope and downstream distance for time of exposure of resistant rocks. Channel and unconformity slopes are measured from a suite of channels developed on resistant Paleozoic limestone exhumed by the removal of Cenozoic sediments from the Baybeiche Range bordering the Naryn basin in the western Tian Shan. The compiled data set, sampling five orders-of-magnitude of upstream drainage area (0.03 to 227 km 2 ), is used to derive the exponent, n , relating channel steepness to channel incision rate, and the ratio, K / V of the rate constant for channel incision of the resistant substrate, K , to the erosion rate, V , of the cover strata. We show that for a typical value of intrinsic concavity (slope-area exponent, θ  = 0.5), erosion rates that are proportional to specific stream power ( n  = 1) satisfy the data set. However, valley-width data suggest that the intrinsic concavity is higher ( θ  = 0.8) and that the channel-incision data can also be fit if erosion is proportional to basal shear stress ( n  = 2/3). Our results do not support values of n significantly greater than one. Using 36 Cl exposure age-dating of the unconformity surface, we independently demonstrate that theCenozoic cover strata have been progressively stripped downward from the unconformity surface at a vertical rate of 1 to 2 m/kyr. Using V  = 1 m/kyr, we constrain the rate constant, K , to between 6 ± 1 and 9 ± 2 × 10 − 4 kyr − 1 for incision of resistant limestone bedrock in this field setting.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2014-10-16
    Description: Article Extreme rainfall events in the eastern Central Andes can result in substantial economic and ecological damage, yet their prediction is difficult. Here, the authors introduce the concept of network divergence and propose a general framework for the prediction of extreme events. Nature Communications doi: 10.1038/ncomms6199 Authors: N. Boers, B. Bookhagen, H. M. J. Barbosa, N. Marwan, J. Kurths, J. A. Marengo
    Electronic ISSN: 2041-1723
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 4
    Publication Date: 2014-03-16
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2017-05-23
    Description: Streams commonly respond to base-level fall by localizing erosion within steepened, convex knickzone reaches. Localized incision causes knickzone reaches to migrate upstream. Such migrating knickzones dictate the pace of landscape response to changes in tectonics or erosional efficiency and can help quantify the timing and source of base-level fall. Identification of knickzones typically requires individual selection of steepened reaches: a process that is tedious, subjective, and has no efficient means to measure knickzone size. We construct an algorithm to automate this procedure by selecting the bounds of knickzone reaches in a χ-space (drainage-area normalized) framework. An automated feature calibrates algorithm parameters to a subset of knickzones handpicked by the user. The algorithm uses these parameters as consistent criteria to identify knickzones objectively and then the algorithm measures the height, length, and slope of each knickzone reach. We test the algorithm on 1-, 10-, and 30-m resolution DEMs of six catchments (trunk-stream lengths: 2.1 – 5.4 km) on Santa Cruz Island, southern California. On the 1-m DEM, algorithm-selected knickzones confirm 93% of handpicked knickzone positions (n = 178) to a spatial accuracy ≤100 m, 88% to an accuracy within 50 m, and 46% to an accuracy within 10 m. Using 10 and 30-m DEMs, accuracy is similar: 88-86% to ≤100 m and 82% to ≤50 m (n = 38, 36, respectively). The algorithm enables efficient regional comparison of the size and location of knickzones with geologic structures, mapped landforms, and hillslope morphology, thereby facilitating approaches to characterize the dynamics of transient landscapes.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2017-04-25
    Description: The cryosphere in mountain regions is rapidly declining, a trend that is expected to accelerate over the next several decades due to anthropogenic climate change. A cascade of effects will result, extending from mountains to lowlands with associated impacts on human livelihood, economy, and ecosystems. With rising air temperatures and increased radiative forcing, glaciers will become smaller and, in some cases, disappear, the area of frozen ground will diminish, the ratio of snow to rainfall will decrease, and the timing and magnitude of both maximum and minimum streamflow will change. These changes will affect erosion rates, sediment, and nutrient flux, and the biogeochemistry of rivers and proglacial lakes, all of which influence water quality, aquatic habitat, and biotic communities. Changes in the length of the growing season will allow low-elevation plants and animals to expand their ranges upward. Slope failures due to thawing alpine permafrost, and outburst floods from glacier- and moraine-dammed lakes will threaten downstream populations. Societies even well beyond the mountains depend on meltwater from glaciers and snow for drinking water supplies, irrigation, mining, hydropower, agriculture, and recreation. Here, we review and, where possible, quantify the impacts of anticipated climate change on the alpine cryosphere, hydrosphere, and biosphere, and consider the implications for adaptation to a future of mountains without permanent snow and ice.
    Electronic ISSN: 2328-4277
    Topics: Geosciences
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  • 7
    Publication Date: 2012-08-08
    Description: Several processes contribute to denudation in high-mountain environments. Of these, glacial erosion is particularly difficult to constrain, despite its critical importance in the evolution of many mountain ranges. In this study, we present a new data set of 10Be concentrations in fluvial sediments sampled along the Marsyandi River and its main tributaries in central Nepal. We interpret the 10Be concentrations as being significantly impacted by glacially derived sediments along the Marsyandi River. Such additions complicate conventional interpretations of 10Be-derived catchment-scale denudation rates. Using a simple linear mass-conservation formulation, we invert our data set in order to separate the different denudational contributions to the observed signal, as well as to constrain their magnitude and spatial distribution. Our results suggest significant variations in glacial erosion, both in space and magnitude, within the Marsyandi catchment.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    Publication Date: 2016-11-13
    Description: Recent studies have shown that the 1976-1977 global climate shift strongly affected South American climate. In our study, we observed a link between this climate shift and river-discharge variability in the subtropical Southern Central Andes. We analyzed daily river-discharge time series between 1940 and 1999 from small to medium mountain drainage basins (10 2 -10 4 km 2 ) across a steep climatic and topographic gradient. We document that the discharge frequency-distribution changed significantly, with higher percentiles exhibiting more pronounced trends. A change point between 1971 and 1977 marked an intensification of the hydrological cycle, which resulted in increased river discharge. In the upper Rio Bermejo basin of the northernmost Argentine Andes, the mean annual discharge increased by 40% over seven years. Our findings are important for flood risk management in areas impacted by the 1976-1977 climate shift; discharge-frequency distribution analysis provides important insights into the variability of the hydrological cycle in the Andean realm.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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