Home About us Contact
|
Home About us Contact | ||
|
|
||
Melt Water (melt + water)
Selected AbstractsRecharge and Preservation of Laurentide Glacial Melt Water in the Canadian ShieldGROUND WATER, Issue 5 2000Ian D. Clark Ground water inflows to drifts ranging from 700 to 1615 m below ground surface at the Con Mine, Yellowknife, Northwest Territories, Canada, were used to study deep hydrogeological flow regimes in Shield terrain. Salinity trends are due to mixing between low-TDS ground water and deep Ca(Na)-C1 brines (>290 g/L) likely derived from Devonian sea water. C1 - ,,18O relationships demonstrate that all inflows are a mixture of three distinct components: modern meteoric ground water (,18O ,,18.9 ± 0.1%o), brine (,18O ,,10%o), and an isotopically depleted water (,18O ,,28%o). The origin of this third endmember is attributed to glacial melt water injected into the subsurface during ablation of the Laurentide Ice Sheet at ca. 10 ka. A mechanism is proposed where high hydrostatic pressure in the ablation zone imposes strong downward gradients beneath the ice sheet margin. Numerical simulation with the SWIFT II finite-difference code recreates the observed salinity gradients within a modeled 50-year interval, corresponding with the rate of retreat of the ice sheet across the landscape at this time. The persistence of this melt water in the subsurface for some 10,000 years following retreat of the ice and decay of the steep hydraulic gradients highlights the importance of gradient, in addition to permeability, as a major control on ground water flow and transport in deep crystalline settings. [source] Structural composition and sediment transfer in a composite cirque glacier: Glacier de St. Sorlin, FranceEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2008Sam Roberson Abstract This paper considers the links between structure, sediment transport and sediment delivery at Glacier de St. Sorlin, France. Sediment transported by the glacier is concentrated at flow-unit boundaries as medial moraines, controlled by the position of bedrock outcrops in the accumulation area. Rockfall entrained within primary stratification is tightly folded at flow-unit boundaries under high cumulative strains and laterally compressive stress. High cumulative strains and laterally compressive stresses lead to the development of longitudinal foliation from primary stratification. Folding elevates subglacial sediments into foliation-parallel debris ridges, which are exposed in the ablation area. Crevasses and shear planes within the glacier have little control on sediment transport. Debris stripes in the proglacial area are morphologically similar to foliation-parallel debris ridges; however, they are not structurally controlled, but formed by fluvial erosion. The conclusion of this study is that at Glacier de St. Sorlin proglacial sediment-landform associations are subjected to intense syn- and post-depositional modification by high melt-water discharges, hence their composition does not reflect that of sediments melting out at the terminus. The action of melt water limits the potential of the sedimentary record to be used to constrain numerical models of past glacier dynamics in debris-poor glacierized Alpine catchments. Copyright © 2008 John Wiley & Sons, Ltd. [source] Recharge and Preservation of Laurentide Glacial Melt Water in the Canadian ShieldGROUND WATER, Issue 5 2000Ian D. Clark Ground water inflows to drifts ranging from 700 to 1615 m below ground surface at the Con Mine, Yellowknife, Northwest Territories, Canada, were used to study deep hydrogeological flow regimes in Shield terrain. Salinity trends are due to mixing between low-TDS ground water and deep Ca(Na)-C1 brines (>290 g/L) likely derived from Devonian sea water. C1 - ,,18O relationships demonstrate that all inflows are a mixture of three distinct components: modern meteoric ground water (,18O ,,18.9 ± 0.1%o), brine (,18O ,,10%o), and an isotopically depleted water (,18O ,,28%o). The origin of this third endmember is attributed to glacial melt water injected into the subsurface during ablation of the Laurentide Ice Sheet at ca. 10 ka. A mechanism is proposed where high hydrostatic pressure in the ablation zone imposes strong downward gradients beneath the ice sheet margin. Numerical simulation with the SWIFT II finite-difference code recreates the observed salinity gradients within a modeled 50-year interval, corresponding with the rate of retreat of the ice sheet across the landscape at this time. The persistence of this melt water in the subsurface for some 10,000 years following retreat of the ice and decay of the steep hydraulic gradients highlights the importance of gradient, in addition to permeability, as a major control on ground water flow and transport in deep crystalline settings. [source] Transformations of runoff chemistry in the Arctic tundra, Northwest Territories, CanadaHYDROLOGICAL PROCESSES, Issue 14 2006W. L. Quinton Abstract The transformation of snowmelt water chemical composition during melt, elution and runoff in an Arctic tundra basin is investigated. The chemistry of the water flowing along pathways from the surface of melting snow to the 95·5 ha basin outlet is related to relevant hydrological processes. In so doing, this paper offers physically based explanations for the transformation of major ion concentrations and loads of runoff water associated with snowmelt and rainfall along hydrological pathways to the stream outlet. Late-lying snowdrifts were found to influence the ion chemistry in adjacent reaches of the stream channel greatly. As the initial pulse of ion-rich melt water drained from the snowdrift and was conveyed through hillslope flowpaths, the concentrations of most ions increased, and the duration of the peak ionic pulse lengthened. Over the first 3 m of overland flow, the concentrations of all ions except for NO increased by one to two orders of magnitude, with the largest increase for K+, Ca2+ and Mg2+. This was roughly equivalent to the concentration increase that resulted from percolation of relatively dilute water through 0·25 m of unsaturated soil. The Na+ and Cl, were the dominant ions in snowmelt water, whereas Ca2+ and Mg2+ dominated the hillslope runoff. On slopes below a large melting snowdrift, ion concentrations of melt water flowing in the saturated layer of the soil were very similar to the relatively dilute concentrations found in surface runoff. However, once the snowdrift ablated, ion concentrations of subsurface flow increased above parent melt-water concentrations. Three seasonally characteristic hydrochemical regimes were identified in a stream reach adjacent to late-lying snowdrifts. In the first two stages, the water chemistry in the stream channel strongly resembled the hillslope drainage water. In the third stage, in-stream geochemical processes, including the weathering/ion exchange of Ca2+ and Mg2+, were the main control of streamwater chemistry. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||