scholarly journals Long-term background denudation rates of southern and southeastern Brazilian watersheds estimated with cosmogenic 10Be

Geomorphology ◽  
2016 ◽  
Vol 268 ◽  
pp. 54-63 ◽  
Author(s):  
Veronica Sosa Gonzalez ◽  
Paul R. Bierman ◽  
Nelson F. Fernandes ◽  
Dylan H. Rood
Keyword(s):  
Denudation Rates ◽  
Cosmogenic 10Be

scholarly journals Climatic effects on rapid chemical and physical denudation rates measured with cosmogenic nuclides in the Ōhau catchment, New Zealand

2021 ◽  
Author(s):  
◽  
Maia Bellingham
Keyword(s):  
Carbon Dioxide ◽  
New Zealand ◽  
Chemical Weathering ◽  
Southern Alps ◽  
Grain Sizes ◽  
Denudation Rates ◽  
Climate Stability ◽  
Mountain Landscapes ◽  
Carbon Dioxide Cycling

<p>Understanding how active mountain landscapes contribute to carbon dioxide cycling and influences on long-term climate stability requires measurement of weathering fluxes from these landscapes. The few measured chemical weathering rates in the Southern Alps are an order of magnitude greater than in the rest of the world. Rapid tectonic uplift coupled with extreme orographic precipitation is driving exceptionally fast chemical and physical denudation. These rates suggest that weathering in landscapes such as the Southern Alps could play a significant role in carbon dioxide cycling. However, the relative importance of climate and tectonics driving these fast rates remains poorly understood.   To address this gap, in situ ¹⁰Be derived catchment-averaged denudation rates were measured in the Ōhau catchment, Canterbury, New Zealand. Denudation rates in the Dobson Valley within the Ōhau catchment, varied from 474 – 7,570 m Myr⁻¹, aside from one sub-catchment in the upper Dobson Valley that had a denudation rate of 12,142 m Myr⁻¹. The Dobson and Hopkins Rivers had denudation rates of 1,660 and 4,400 m Myr⁻¹ respectively, in these catchments. Dobson Valley denudation rates show a moderate correlation with mean annual precipitation (R²=0.459). This correlation supports a similar trend identified at local and regional scales, and at high rates of precipitation this may be an important driver of erosion and weathering.   Sampling of four grain sizes (0.125 to > 8 mm) at one site in the Dobson Valley resulted in variability in ¹⁰Be concentrations up to a factor of 2.5, which may be a result of each grain size recording different erosional processes. These observations demonstrate the importance of assessing potential variability and the need to sample consistent grain sizes across catchments.   Chemical depletion fractions measured within soil pits in the upper Dobson Valley indicate chemical weathering contributes 30% of total denudation, and that physical erosion is driving rapid total denudation. Chemical weathering appears to surpass any proposed weathering speed limit and suggests total weathering may not be limited by weathering kinetics. This research adds to the paucity of research in New Zealand, and for the first time presents ¹⁰Be derived denudation rates from the eastern Southern Alps, with estimates of the long-term weathering flux. High weathering fluxes in the Southern Alps uphold the hypothesis that mountain landscapes play an important role in carbon dioxide cycling and long-term climate stability.</p>

scholarly journals The role of frost cracking in local denudation of steep Alpine rockwalls over millennia (Eiger, Switzerland)

2020 ◽  
Vol 8 (3) ◽  
pp. 637-659
Author(s):  
David Mair ◽  
Alessandro Lechmann ◽  
Romain Delunel ◽  
Serdar Yeşilyurt ◽  
Dmitry Tikhomirov ◽  
...  
Keyword(s):  
Swiss Alps ◽  
Rock Fall ◽  
Temperature Changes ◽  
Rock Face ◽  
Temperature Conditions ◽  
Denudation Rates ◽  
Reconstructed Temperature ◽  
Cryogenic Processes

Abstract. Denudation of steep rockwalls is driven by rock fall processes of various sizes and magnitudes. Rockwalls are sensitive to temperature changes mainly because thermo-cryogenic processes weaken bedrock through fracturing, which can precondition the occurrence of rock fall. However, it is still unclear how the fracturing of rock together with cryogenic processes impacts the denudation processes operating on steep rockwalls. In this study, we link data on long-term rockwall denudation rates at the Eiger (Central Swiss Alps) with the local bedrock fabric and the reconstructed temperature conditions at these sites, which depend on the insolation pattern. We then estimate the probability of bedrock for failure through the employment of a theoretical frost cracking model. The results show that the denudation rates are low in the upper part of the NW rockwall, but they are high both in the lower part of the NW rockwall and on the SE face, despite similar bedrock fabric conditions. The frost cracking model predicts a large difference in cracking intensity from ice segregation where the inferred efficiency is low in the upper part of the NW rockwall but relatively large on the lower section of the NW wall and on the SE rock face of the Eiger. We explain this pattern by the differences in insolation and temperature conditions at these sites. Throughout the last millennium, temperatures in bedrock have been very similar to the present. These data thus suggest the occurrence of large contrasts in microclimate between the NW and SE walls of the Eiger, conditioned by differences in insolation. We use these contrasts to explain the relatively low denudation rates in the upper part of the NW rockwall and the rapid denudation in the SW face and in the lower part of the NW rock face where frost cracking is more efficient.

scholarly journals Denudation systematics inferred from in situ cosmogenic <sup>10</sup>Be concentrations in fine (50–100 µm) and medium (100–250 µm) sediments of the Var River basin, southern French Alps

2019 ◽  
Vol 7 (4) ◽  
pp. 1059-1074 ◽  
Author(s):  
Apolline Mariotti ◽  
Pierre-Henri Blard ◽  
Julien Charreau ◽  
Carole Petit ◽  
Stéphane Molliex ◽  
...  
Keyword(s):  
Glacial Cycles ◽  
Size Fractions ◽  
French Alps ◽  
Fine Grained ◽  
Denudation Rates ◽  
Variable Morphology ◽  
Cosmogenic 10Be ◽  
The Impact ◽  
Quartz Grains

Abstract. Marine sedimentary archives are well dated and often span several glacial cycles; cosmogenic 10Be concentrations in their detrital quartz grains could thus offer the opportunity to reconstruct a wealth of past denudation rates. However, these archives often comprise sediments much finer (<250 µm) than typically analyzed in 10Be studies, and few studies have measured 10Be concentrations in quartz grains smaller than 100 µm or assessed the impacts of mixing, grain size, and interannual variability on the 10Be concentrations of such fine-grained sediments. Here, we analyzed the in situ cosmogenic 10Be concentrations of quartz grains in the 50–100 and 100–250 µm size fractions of sediments from the Var basin (southern French Alps) to test the reliability of denudation rates derived from 10Be analyses of fine sands. The Var basin has a short transfer zone and highly variable morphology, climate, and geology, and we test the impact of these parameters on the observed 10Be concentrations. Both analyzed size fractions returned similar 10Be concentrations in downstream locations, notably at the Var's outlet, where concentrations ranged from (4.02±0.78)×104 to (4.40±0.64)×104 atoms g−1 of quartz. By comparing expected and observed 10Be concentrations at three major river junctions, we interpret that sediment mixing is efficient throughout the Var basin. We resampled four key locations 1 year later, and despite variable climatic parameters during that period, interannual 10Be concentrations were in agreement within uncertainties, except for one upper subbasin. The 10Be-derived denudation rates of Var subbasins range from 0.10±0.01 to 0.57±0.09 mm yr−1, and spatial variations are primarily controlled by the average subbasin slope. The integrated denudation rate of the entire Var basin is 0.24±0.04 mm yr−1, in agreement with other methods. Our results demonstrate that fine-grained sediments (50–250 µm) may return accurate denudation rates and are thus potentially suitable targets for future 10Be applications, such as studies of paleo-denudation rates using offshore sediments.

scholarly journals Long- to short-term denudation rates in the southern Apennines: geomorphological markers and chronological constraints

2011 ◽  
Vol 62 (1) ◽  
pp. 27-41 ◽  
Author(s):  
Dario Gioia ◽  
Claudio Martino ◽  
Marcello Schiattarella
Keyword(s):  
Sediment Accumulation ◽  
Radiometric Dating ◽  
Sedimentation Rates ◽  
Southern Apennines ◽  
Short Term ◽  
Small Catchment ◽  
Fluvial Terraces ◽  
Denudation Rates ◽  
Land Surfaces

Long- to short-term denudation rates in the southern Apennines: geomorphological markers and chronological constraints Age constraints of geomorphological markers and consequent estimates of long- to short-term denudation rates from southern Italy are given here. Geomorphic analysis of the valley of the Tanagro River combined with apatite fission track data and radiometric dating provided useful information on the ages and evolution of some significant morphotectonic markers such as regional planated landscapes, erosional land surfaces and fluvial terraces. Reconstruction of paleotopography and estimation of the eroded volumes were perfomed starting from the plano-altimetric distribution of several orders of erosional land surfaces surveyed in the study area. Additional data about denudation rates related to the recent and/or active geomorphological system have been obtained by estimating the amount of suspended sediment yield at the outlet of some catchments using empirical relationships based on the hierarchical arrangement of the drainage network. Denudation rates obtained through these methods have been compared with the sedimentation rates calculated for two adjacent basins (the Pantano di San Gregorio and the Vallo di Diano), on the basis of published tephrochronological constraints. These rates have also been compared with those calculated for the historical sediment accumulation in a small catchment located to the north of the study area, with long-term exhumation data from thermochronometry, and with uplift rates from the study area. Long- and short-term denudation rates are included between 0.1 and 0.2 mm/yr, in good agreement with regional data and long-term sedimentation rates from the Vallo di Diano and the Pantano di San Gregorio Magno basins. On the other hand, higher values of exhumation rates from thermochronometry suggest the existence of past erosional processes faster than the recent and present-day exogenic dismantling. Finally, the comparison between uplift and denudation rates indicates that the fluvial erosion did not match the tectonic uplift during the Quaternary in this sector of the chain. The axial zone of the southern Apennines should therefore be regarded as a landscape in conditions of geomorphological disequilibrium.

scholarly journals <sup>10</sup>Be depth profiles in glacial sediments on the Swiss Plateau: deposition age, denudation and (pseudo-) inheritance

2017 ◽  
Vol 66 (2) ◽  
pp. 57-68 ◽  
Author(s):  
Lorenz Wüthrich ◽  
Claudio Brändli ◽  
Régis Braucher ◽  
Heinz Veit ◽  
Negar Haghipour ◽  
...  
Keyword(s):  
Radioactive Decay ◽  
Glacial Sediments ◽  
Depth Profiles ◽  
Denudation Rates ◽  
Last Glaciation ◽  
The Alps ◽  
Swiss Plateau ◽  
High Concentrations ◽  
Cosmogenic 10Be

Abstract. During the Pleistocene, glaciers advanced repeatedly from the Alps onto the Swiss Plateau. Numeric age control for the last glaciation is good and thus the area is well suited to test a method which has so far not been applied to till in Switzerland. In this study, we apply in situ produced cosmogenic 10Be depth profile dating to several till deposits. Three sites lie inside the assumed Last Glacial Maximum (LGM) extent of the Rhône and Aare glaciers (Bern, Deisswil, Steinhof) and two lie outside (Niederbuchsiten, St. Urban). All sites are strongly affected by denudation, and all sites have reached steady state, i.e., the 10Be production is in equilibrium with radioactive decay and denudational losses. Deposition ages can therefore not be well constrained. Assuming constant denudation rates of 5 cm kyr−1, total denudation on the order of 100 cm for sites within the extent of the LGM and up to tens of meters for older moraines are calculated. Denudation events, for example related to periglacial conditions during the LGM, mitigate the need to invoke such massive denudation and could help to explain high 10Be concentrations at great depths, which we here dub pseudo-inheritance. This term should be used to distinguish conceptionally from true inheritance, i.e., high concentrations derived from the catchment.

scholarly journals Millennial-scale denudation rates in the Himalaya of Far Western Nepal

2019 ◽  
Author(s):  
Lujendra Ojha ◽  
Ken L. Ferrier ◽  
Tank Ojha
Keyword(s):  
Stream Power ◽  
Denudation Rate ◽  
The Past ◽  
Cosmogenic Nuclide ◽  
Northern India ◽  
Denudation Rates ◽  
Cosmogenic 10Be ◽  
Channel Steepness ◽  
The Himalaya ◽  
Millennial Scale

Abstract. Over the past two decades, rates and patterns of Himalayan denudation have been documented through numerous cosmogenic nuclide measurements in central and eastern Nepal, Bhutan, and northern India. To date, however, few denudation rates have been measured in Far Western Nepal – a ~ 300-km-wide region near the center of the Himalayan arc – which presents a significant gap in our understanding of Himalayan denudation. Here we report new catchment-averaged millennial-scale denudation rates inferred from cosmogenic 10Be in fluvial quartz at seven sites in Far Western Nepal. The inferred denudation rates range from 385 ± 31 t km−2 yr−1 (0.15 ± 0.01 mm yr −1) to 8737 ± 2908 t km−2 yr−1 (3.3 ± 1.1 mm yr−1), and, in combination with our analyses of channel topography, are broadly consistent with previously published relationships between catchment-averaged denudation rates and normalized channel steepness across the Himalaya. These data show a weak correlation with catchment-averaged specific stream power, consistent with a Himalaya-wide compilation of previously published stream power values. Together, these observations are consistent with a dependence of denudation rate on both tectonic and climatic forcings, and represent a first step toward filling an important gap in denudation rate measurements in Far Western Nepal.

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