Asynchronous glacier dynamics during the Antarctic Cold Reversal in central Patagonia

We present 14 new 10Be cosmogenic nuclide exposure ages quantifying asynchronous readvances during the Antarctic Cold Reversal from glaciers in the Baker Valley region of central Patagonia. We constrain glacier and ice-dammed palaeolake dynamics using a landsystems approach, concentrating on outlet glaciers from the eastern Northern Patagonian Icefield (NPI) and Monte San Lorenzo (MSL). Soler Glacier (NPI) produced lateral moraines above Lago Bertrand from 15.1 ± 0.7 to 14.0 ± 0.6 ka, when it dammed the drainage of Lago General Carrera/Buenos Aires through Río Baker at a bedrock pinning point. At this time, Soler Glacier terminated into the 400 m “Deseado” level of the ice-dammed palaeolake. Later, Calluqueo Glacier (MSL) deposited subaerial and subaqueous moraines in the Salto Valley near Cochrane at 13.0 ± 0.6 ka. These moraines were deposited in an ice-dammed palaeolake unified through the Baker Valley (Lago Chalenko; 350 m asl). The Salto Valley glaciolacustrine landsystem includes subaqueous morainal banks, ice-scoured bedrock, glacial diamicton plastered onto valley sides, perched delta terraces, kame terraces, ice-contact fans, palaeoshorelines and subaerial push and lateral moraines. Boulders from the subaqueous Salto Moraine became exposed at 12.1 ± 0.6 years, indicating palaeolake drainage. These data show an asynchronous advance of outlet glaciers from the Northern Patagonian Icefield and Monte San Lorenzo during the Antarctic Cold Reversal. These advances occurred during a period of regional climatic cooling, but differential moraine extent and timing of advance was controlled by topography and calving processes

Mud and metal; the impact of historical mining on the estuaries of SW England, UK

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordVisitors and residents alike enjoy the countryside and coast of SW England because of the stunning landscapes and natural environment. Many will also be aware, largely through the industrial archaeological record and world heritage site designation, of the historical importance of mining in this region. Separate mineralization episodes, primarily during the Permian and Triassic, led to the formation of a world-class polymetallic ore field, with major deposits of not only tin (Sn) and copper (Cu), but also iron (Fe), lead (Pb), arsenic (As), zinc (Zn), tungsten (W) and silver (Ag), along with minor occurrences of less common metals such as uranium (U), antimony (Sb), nickel (Ni), cobalt (Co), bismuth (Bi) and gold (Au). Mining of alluvial deposits commenced in the Bronze Age, with hard rock mining commencing by the late thirteenth century and continuing intermittently, as metal prices rose and fell, to the present day. With hard rock mining, came the processing or ‘dressing’ of ores during which they were crushed so that minerals of interest could be recovered. The wastes from this process—mine tailings—were historically released into rivers and transported towards the coast as man-made sediments. Deposition occurred in many of the estuaries around SW England, which consequently preserve a record of the development and historical impact of mining.CSM TrustCory EntrustEuropean Social FundRSPBFowey Harbour Commissioner

Geomorphologic impact of outburst flood cycle in braided gravel-bed rivers: confluence of Colonia and Baker rivers, Patagonia, Chile

Colonia River, as other glacial streams influenced by global warming, is affected by Glacial Lake Outburst Floods (OF). We present a study on geomorphologic features of Colonia River to comprehend the impact of OFs in sedimentary processes, analysing erosion and deposition linked to OF phenomena and frequency (since April 2008, more than 12 OFs have occurred). Interpolation analysis is carried out to create an elevation surface (DTM) from a set of sample measurements, given by contour line (2007 LiDAR) and rtkGPS point (2011 and 2012) data. These were used to create DTMs applying Delaunay triangulation. A comparisons between morphology during the current OF cycle that started on 8 April 2008, and the previous morphology (after 40 years without OFs, since end of previous cycle in 1968), is carried out through the creation of DEMs of Difference (DoDs) based on TINs. We created two DoDs, respectively between 2011-2007 (before/after the OFs cycle) and 2012-2011 (during the cycle, after the events of January and April 2012) to provide a high-resolution, spatially distributed surface model of topographic and volumetric change through time. The floodplain has been classified on the basis of the morphological characteristics: main and secondary channel(s), bars, braided area, island and delta fan features. The changes evidenced in the DoD are segregated according to these categories plus the geomorphic change taking place in each category (using GCD; Wheaton et al 2014). Issues regarding data quantity and quality will be discussed, and implications for the planned mega-dam that would flood the confluence

Declining discharge of glacier outburst floods through the Holocene in Central Patagonia

Glacier outburstfloods are a major hazard in glacierized catchments. Global analyses have shownreduced frequency of glacierfloods over recent decades but there is limited longer-term data on eventmagnitude and frequency. Here, we present a Holocene palaeoflood record from the Río Baker (ChileanPatagonia), quantifying the discharge and timing of glacierfloods over millennial timescales. A cata-strophicflood of 110,000 m3/s (0.11 Sv) occurred at 9.6±0.8 ka, duringfinal stages of the Late GlacialInterglacial Transition, followed byfiveflood-phases coeval or post-dating Holocene neoglacials. Highestflood frequencies occurred at 4.3e4.4 ka, with 26floods of minimum discharges of 10,000e11,000 m3/s,and 0.6 ka with 10floods exceeding 4600e5700 m3/s. The largest modern outburstflood recordedsurpassed ~3810 m3/s. Thus glacierflood magnitude declines from the order of 0.1 to 0.01 Sv over theEarly to Mid Holocene, and to 0.001 Sv in the instrumental record.GB was supported by the Spanish Ministry of Science, Innovation and Universities. VT would like to thank the Natural Resources Defence Council and Royal Holloway University of London Research Strategy Fund (RHUL-RSF) for funding initialfield visits that led tothis research. AD thanks equipment and field support from CIEP, B.Reid, DGA-Aysen, J. Tureo, C. Meier, C. Olivares, H. Soto, M. Williams(U Greenwich) and NERC-GEF. Xavier Rodriguez-Lloveras providedfield assistance duringfield work in April 2014.Peer reviewe

Magnitude and timing of Holocene glacial lake outburst floods in the Baker River, Northern Patagonian Icefield, Chile / Magnitud y frecuencia de inundaciones Holocenas generadas por vaciamiento de lagos glaciares en el Rio Baker, Campo de Hielo, Patagonico Norte, Chile

The Baker River (Southern Chile) drains a catchment of 27,000 km2 and has a mean annual discharge of 1100 m3s-1. Since last deglaciation, the morpho-sedimentology of the Baker valley has been controlled by Outburst Floods (OFs) of different scales. We apply geomorphic mapping, stratigraphy (including radiocarbon and OSL dating) and palaeoflood hydrology to reconstruct the frequency, timing and magnitude of Holocene OFs. Geomorphic mapping reveals evidence of two Holocene alluvial terraces. The oldest (highest) contains basal gravels capped by a well-developed buried Podzolic Luvisol that was radiocarbon dated to 6160±40 BP. In this alluvial sequence, at least two major floods occurred between then and 5300 BP and at least eight major floods between 5300-2500 BP. At least three Late Holocene (post 610±30 BP) GLOF event(s) inundated upper terrace surfaces along the reach downstream the confluence of the Colonia River into the Baker River. We report on the implications of this palaeoflood research in relation to the proposed HydroAysén hydroelectric scheme

Hydrological response of a dryland ephemeral river to southern African climatic variability during the last millennium

12 páginas, 6 figuras, 2 tablas.-- El PDF del artículo esta en su versión post print.A long-term flood record from the Buffels River, the largest ephemeral river of NW South Africa (9250 km2), was reconstructed based on interpretation of palaeoflood, documentary and instrumental rainfall data. Palaeoflood data were obtained at three study reaches, with preserved sedimentary evidence indicating at least 25 large floods during the last 700 yr. Geochronological control for the palaeoflood record was provided by radiocarbon and optically stimulated luminescence (OSL) dating. Annual resolution was obtained since the 19th century using the overlapping documentary and instrumental records. Large floods coincided in the past within three main hydroclimatic settings: (1) periods of regular large flood occurrence (1 large flood/~30 yr) under wetter and cooler prevailing climatic conditions (AD 1600–1800), (2) decreasing occurrence of large floods (1 large flood/~100 yr) during warmer conditions (e.g., AD 1425–1600 and after 1925), and (3) periods of high frequency of large floods (~ 4–5 large floods in 20–30 yr) coinciding with wetter conditions of decadal duration, namely at AD 1390–1425, 1800–1825 and 1915–1925. These decadal-scale periods of the highest flood frequency seem to correspond in time with changes in atmospheric circulation patterns, as inferred when comparing their onset and distribution with temperature proxies in southern Africa.The study was funded by the 6th Framework Programme of the European Commission through the project “FloodWater recharge of alluvial Aquifers in Dryland Environments”, WADE Project (contract no. GOCE-CT-2003-506680).Peer reviewe

Efectos de las fuentes cartográficas en los resultados de la modelación hidráulica de crecidas

[ES] En este trabajo se ha analizado el efecto de la cartografía en los resultados derivados de los modelos hidráulicos. Se han creado siete modelos de elevaciones del terreno (MDT) desarrollados a partir de tres fuentes cartográficas diferentes: un levantamiento por posicionamiento global GPS, un modelo digital de elevaciones a partir de datos altimétricos de alta resolución LiDAR (Light Detection And Ranging) y una cartografía vectorial de curvas de nivel. Los modelos cartográficos de partida han sido analizados y los resultados del modelo hidráulico se evaluaron en tres contextos diferentes: 1) los propios resultados del modelo: relación caudal-altura de la lámina de agua, 2) la sensibilidad relativa del modelo hidráulico a cambios en el parámetro de resistencia al flujo según el modelo cartográfico utilizado y 3) la delineación del área de inundación. Los cálculos hidráulicos se han basado en un modelo unidimensional (HEC-RAS). El trabajo demuestra la importancia de los modelos cartográficos, al obtener variaciones de 4.5 m en la determinación de la altura de la lámina de agua y de un 50% en la estimación del área inundada para las mismas condiciones de contorno.Este trabajo ha sido realizado en el ámbito del proyecto SPHERE (Systematic, Palaeoflood and Historical data for the improvEment of flood Risk Estimation), financiado por la Comisión Europea (contract number EVG1-CT-1999-00010), y del proyecto PALEOCAP financiado por la CICYT (REN2001-1633/RIES).Casas Planes, A.; Benito, G.; Thorndycraft, VR.; Rico, M. (2005). Efectos de las fuentes cartográficas en los resultados de la modelación hidráulica de crecidas. Ingeniería del agua. 12(4):309-320. https://doi.org/10.4995/ia.2005.2567309320124Ackermann, F. (1999). Airborne laser scanning - present status and future expectations.ISPRS Journal of Photogrammetry & Remote Sensing, 54, pp. 64-67.Baltsavias, E.P. (1999). 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Earth Surface Proceses and Landforms, 25, pp. 973-990.Burrough, P.A., McDonnell, R.A. (1998). Principals of Geographical Information Systems, Oxford University Press.Charlton, M.E, Large, A.R.G., Fuller, I.C. (2003). "Application of airborne LiDAR in River environments: The River Coquet, Northumberland, UK" Earth Surface Processes and Landforms, 28, pp. 299-306.Chow V.T., Maidment D.R, Mays L.W. (1988). Applied Hydrology, MacGraw-Hill, Inc., New York.Cobby, D.M., Mason, D.C. (1999). "Image processing of airborne scanning laser altimetry for improved river flood modeling". ISPRS Journal of Photogrammetry and Remote Sensing, 56, pp. 121-138.Cobby, D.M., Mason, D.C., Horritt, M.S., Bates, P.D. (2003). "Two-dimensional hydraulic flood modelling using a finite-element mesh decomposed according to vegetation and topographic features derived from airborne scanning laser altimetry" Hydrological Processes, 17, pp. 1979-2000.Fix R.E., Burt T.P. (1995). "Global Positioning System: an effective way to map a small catchment". Earth Surface Proceses and Landforms, 20, pp. 817-827.French, J.R. (2003) "Airborne LiDAR in support of geomorphological and hydraulic modelling", Earth Surface Processes and Landforms, 28, pp. 321-335.Gomes Pereira, L.M., Wicherson, R.J. (1999). "Suitability of laser data for deriving geographical information: a case study in the context of management of fluvial zones". ISPRS Journal of Photogrammetry and Remote Sensing, 54 (2-3), pp. 105-114.Hardy, R.J., Bates, P.D., Anderson, M.G. (1999). "The importance of spatial resolution in hydraulic models for floodplain environments". Journal of Hydrology, 216, pp. 124-136.Horritt, M.S. (2000). "Development of physically based meshes for two-dimensional models of meandering channel flow". International Journal for numerical methods in engineering, 47, pp. 2019-2037.Horritt, M.S., Bates, P.D. (2001a). "Predicting floodplain inundation: rasted-based modelling versus the finite-element approach". Hydrological Processes, 15 (5), pp. 825-842.Horritt, M.S., Bates, P.D. (2001b). "Effects of spatial resolution on a raster based model of flood flow". Journal of Hydrology, 253, pp. 239-249.Hydrologic Engineering Center (1998a). HEC-RAS, River Analysis System User's Manual, Version 3.1, Davis, California.Hydrologic Engineering Center (1998b). HEC-RAS Hydraulic Reference Manual, Davis, California.Hydrologic Engineering Center (2002). HEC-GeoRAS: An extensión for support of HEC-RAS using Arcview User's Manual, Versión 3.1, Davis, California.Keim, R.F., Skaugset, A.E., Bateman, D.S. (1999). "Digital terrain modeling of small stream channels with a total-station theodolite". Advances in water resources, 23, pp. 41-48Lane S.N., Chandler J.H., Richards K.S. (1994). 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Proceedings of the 7th International Conference on Geocomputation. University of Southampton, U.K

High resolution lake sediment record reveals self-organized criticality in erosion processes regulated by internal feedbacks

Reconstruction of high-frequency erosion variability beyond the instrumental record requires well-dated, high-resolution proxies from sediment archives. We used computed tomography (CT) scans of finely laminated silt layers from a lake-sediment record in southwest Oregon to quantify the magnitude of natural landscape erosion events over the last 2000years in order to compare with palaeorecords of climate, forest fire, and seismic triggers. Sedimentation rates were modeled from an age-depth relationship fit through five C-14 dates and the 1964AD Cs-137 peak in which deposition time (yrmm(-1)) varied inversely with the proportion of silt sediment measured by the CT profile. This model resulted in pseudo-annual estimates of silt deposition for the last 2000years. Silt accumulation during the past 80years was strongly correlated with river-discharge at annual and decadal scales, revealing that erosion was highly responsive to precipitation during the logging era (1930-present). Before logging the frequency-magnitude relationship displayed a power-law distribution that is characteristic of complex feedbacks and self-regulating mechanisms. The 100-year and 10-year erosion magnitude estimated in a 99-year moving window varied by 1.7 and 1.0 orders of magnitude, respectively. Decadal erosion magnitude was only moderately positively correlated with a summer temperature reconstruction over the period 900-1900AD. Magnitude of the seven largest events was similar to the cumulative silt accumulation anomaly, suggesting these events returned the system' to the long-term mean rate. Instead, the occurrence of most erosion events was related to fire (silt layers preceded by high charcoal concentration) and earthquakes (the seven thickest layers often match paleo-earthquake dates). Our data show how internal (i.e. sediment production) and external processes (natural fires or more stochastic events such as earthquakes) co-determine erosion regimes at millennial time scales, and the extent to which such processes can be offset by recent large-scale deforestation by logging. Copyright (c) 2018 John Wiley & Sons, Ltd