The rapid retreat of the glaciers of the Cordillera Blanca is having a noticeable impact on the downstream hydrology. Although groundwater is a critical hydrologic component that sustains stream flows during the dry season, its characteristics and its contribution to downstream hydrology remain poorly understood. In this study, we analyse the hydrochemical and isotopic properties of potential hydrologic sources mixing in surface streams to characterize the proglacial hydrology in four glacially fed watersheds within the Cordillera Blanca, Peru. Water samples from streams, glacial melt and groundwater were collected in 2008 and 2009 and analysed for major ions and stable isotopes (δ18O and δ2H). Multivariate analysis of variance was used first to identify the hydrochemical and isotopic characteristics (tracers) of the water samples that depend primarily on the water source. Then several analyses, including hierarchical cluster analysis and mixing diagrams, were performed using these source‐dependent tracers, enabling a qualitative description of the key hydrological mechanisms that characterize the study watersheds. Finally, we applied a multi‐component spatial mixing model, the hydrochemical basin characterization method, to quantify the contributions of different water sources to the outflow from the four watersheds. The hydrochemical basin characterization method results show that groundwater is a major component of the discharge during the dry season and that the groundwater contribution to outflow is greater than 24% in all of the valleys. The results are used to develop a conceptual proglacial hydrological model of the Cordillera Blanca valleys. Talus and avalanche cones are identified as key components of the hydrology of the valleys. The talus deposits collect precipitation and runoff from higher elevations (approximately 400 m above the valley floor) and have a residence time that is long enough to actively release substantial volumes of water throughout the dry season. Copyright © 2014 John Wiley & Sons, Ltd.

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The precise tectonic role of the left-lateral Garlock fault in southern California has been controversial. Three proposed tectonic models yield signifi cantly different predictions for the slip rate, history, orientation, and total bedrock offset as a function of distance along strike. In an effort to test these models, we present the fi rst slip-rate estimate for the western Garlock fault that is constrained by radiocarbon dating. A channel (referred to here as Clark Wash) incised into a Latest Pleistocene alluvial fan has been leftlaterally offset at least 66 ± 6 m and no more than 100 m across the western Garlock fault, indicating a left-lateral slip rate of 7.6 mm/ yr (95% confi dence interval of 5.3-10.7 mm/ yr) using dendrochronologically calibrated radiocarbon dates. The timing of aggradational events on the Clark Wash fan corresponds closely to what has been documented elsewhere in the Mojave Desert, suggesting that much of this activity has been climatically controlled. The range-front fault, located a few hundred meters northwest of the Garlock fault, has probably acted primarily as a normal fault, with a Holocene rate of dip-slip of 0.4-0.7 mm/yr. The record of prehistoric earthquakes on the Garlock fault at this site, though quite possibly incomplete, suggests a longer interseismic interval (1200-2700 yr) for the western Garlock fault than for the central Garlock fault. The relatively high slip rate determined here indicates that the western and central segments of the Garlock fault show similar rates of movement that are somewhat faster than rates inferred from geodetic data. The high rate of motion on the western Garlock fault is most consistent with a model in which the western Garlock fault acts as a conjugate shear to the San Andreas fault. Other mechanisms, involving extension north of the Garlock fault and block rotation at the eastern end of the fault may be relevant to the central and eastern sections of the fault, but they cannot explain a high rate of slip on the western Garlock fault.

We have investigated the geochemistry of supraglacial streams on the Canada Glacier, Taylor Valley, Antarctica during the 2001-2002 austral summer. Canada Glacier supraglacial streams represent the link between primary precipitation (i.e. glacier snow) and proglacial Lake Hoare. Canada Glacier supraglacial stream geochemistry is intermediate between glacier snow and proglacial stream geochemistry with average concentrations of 49.1 leq L )1 Ca 2+ , 19.9 leq L )1 SO 2À 4 , and 34.3 leq L )1 HCO À 3 . Predominant west to east winds lead to a redistribution of readily soluble salts onto the glacier surface, which is reflected in the geochemistry of the supraglacial streams. Western Canada Glacier supraglacial streams have average SO 2À 4 :HCO À 3 equivalent ratios of 1.0, while eastern supraglacial streams average 0.5, suggesting more sulfate salts reach and dissolve in the western supraglacial streams. A graph of HCO À 3 versus Ca 2+ for western and eastern supraglacial streams had slopes of 0.87 and 0.72, respectively with R 2 values of 0.84 and 0.83. Low concentrations of reactive silicate (>10 lmol L )1 ) in the supraglacial streams suggested that little to no silicate weathering occurred on the glacier surface with the exception of cryoconite holes (1000 lmol L )1 ). Therefore, the major geochemical weathering process occurring in the supraglacial streams is believed to be calcite dissolution.Proglacial stream, Anderson Creek, contains higher concentrations of major ions than supraglacial streams containing 5 times the Ca 2+ and 10 times the SO 2À 4 . Canada Glacier proglacial streams also contain higher concentrations (16.6-30.6 leq L )1 ) of reactive silicate than supraglacial streams. This suggests that the controls on glacier meltwater geochemistry switch from calcite and gypsum dissolution to both salt dissolution and silicate mineral weathering as the glacier meltwater evolves.Our chemical mass balance calculations indicate that of the total discharge into Lake Hoare, the final recipient of Canada Glacier meltwater, 81.9% is from direct glacier runoff and 19.1% is from proglacial Andersen Creek. Although during a typical, low melt ablation season Andersen Creek contributes over 40% of the water added to Lake Hoare, its overall chemical importance is diluted by the direct inputs from Canada Glacier during high flow years. Decadal warming

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Unlike temperate and polythermal proglacial streams, the proglacial streams in Taylor Valley (TV), Antarctica, are derived primarily from glacier surface melt with no subglacial or groundwater additions. Solute responses to flow reflect only the interaction of glacial meltwater with the valley floor surrounding the stream channel. We have investigated the major, minor and trace element 24‐h variations of two proglacial melt streams, Andersen Creek and Canada Stream, originating from the Canada Glacier in TV, Antarctica. Both streams exhibited diel mid‐austral summer diurnal flow variation, with maximum flow being more than 50 times the minimum flow. Dissolved (< 0.4 µm) major, minor and trace solute behaviors through diel periods were strongly controlled by the availability of readily solubilized material on the valley floor and hyporheic‐biological exchanges. Anderson Creek had generally greater solute concentrations than Canada Stream because of its greater receipt of eolian sediment. Andersen Creek also acquired greater solute concentrations in the rising limb of the hydrograph than the falling limb because of dissolution of eolian material at the surface of the stream channel coupled with minimal hyporheic‐biological exchange. Conversely, Canada Stream had less available eolian sediment, but a greater hyporheic‐biological exchange, which preferentially removed trace and major solutes in the rising limb and released them in the falling limb. Given the dynamic nature of discharge, eolian, and hyporheic‐biological processes, solute loads in TV streams are difficult to predict. Copyright © 2012 John Wiley & Sons, Ltd.

Abstract:We present concentrations of environmentally available (unfiltered acidified 2% v/v HNO 3 ) As, Cu, Cd, Pb, V, Sr, and major ions including Ca 2C

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