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Glacial Environments (glacial + environment)
Selected AbstractsModification of sediment characteristics during glacial transport in high-alpine catchments: Mount Cook area, New ZealandBOREAS, Issue 4 2004MICHAEL J. HAMBREY The Mount Cook area in the Southern Alps of New Zealand is heavily glacierized with numerous peaks over 3000 m a.s.l. feeding several large valley glaciers. The region is subject to rapid tectonic uplift and heavy precipitation (up to 15 m per year). This paper describes the clast roundness, clast shape and textural characteristics associated with five glaciers (Fox, Franz Josef, Hooker, Mueller and Tasman) in terms of inputs to the glacier system, transport by the glaciers and reworking following glacial deposition. Inputs include rockfall, alluvial fan and avalanche material delivered to the surface of valley glaciers. Basal debris, where observed at the terminus of two glaciers, consists mainly of incorporated fluvial material. Following deposition, reworking is mainly by subglacial and proglacial streams. The dominant facies are (i) boulder gravel with mainly angular clasts on the steep slopes above the glaciers, (ii) sandy boulder gravel, with mainly angular and subangular clasts, forming lateral and end moraines, and (iii) sandy boulder/cobble gravel with mainly subrounded clasts, and sand, which represent glacially transported sediment reworked by braided rivers. Diamicton is rare in the contemporary glacial environment. Since most sediment associated with glaciers in the Southern Alps lacks unambiguous indications of glacial transport, interpretation of similar sediments in the geological record should not necessarily exclude the involvement of glacial processes. [source] Hydrologic and geomorphic effects of temporary ice-dammed lake formation during jökulhlaupsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2003Matthew J. Roberts Abstract Glacial outburst ,oods (jökulhlaups) occur frequently in glaciated environments, and the resultant ,ooding causes geomorphic change and, in some instances, damage to local infrastructure. During some jökulhlaups, ,oodwater is stored temporarily in ice-marginal locations. In July 1999, a linearly rising jökulhlaup burst from Sólheimajökull, Iceland. During this remarkable event, subglacial ,oodwater pooled transiently in two relict ice-dammed lake basins, before draining suddenly back into Sólheimajökull. The signi,cance of such rapid formation and attendant drainage of temporary ice-dammed lakes during jökulhlaups has not been addressed. Consequently, this paper: (i) assesses the hydrologic and geomorphic effects of temporary ice-dammed lake formation caused by lake-basin ,retro-,lling'; and (ii) discusses the impact and signi,cance of transient retro-,lling under jökulhlaup conditions. Pre- and post-,ood ,eldwork at Sólheimajökull enabled the impact and signi,cance of lake-basin retro-,lling to be assessed. Field evidence demonstrates that the July 1999 jökulhlaup had an unusually rapid rise to peak discharge, resulting in subglacial ,oodwater being purged to ice-marginal locations. The propensity for temporary retro-,lling was controlled by rapid expulsion of ,oodwater from Sólheimajökull, coincident with locations suitable for ,oodwater storage. Floodwater inundated both ice-marginal lake basins, permitting signi,cant volumes of sediment deposition. Coarse-grained deltas prograding from the ice margin and boulders perched on scoured bedrock provide geomorphic records of sudden retro-,lling. The depositional characteristics of lake-basin deposits at Sólheimajökull are similar to jökulhlaup sediments documented in proglacial settings elsewhere; however, their depositional setting and association with ice-marginal landforms is distinctive. Findings suggest that temporary ice-dammed lake formation and drainage has the capacity to alter the shape of the ,ood hydrograph, especially if drainage of a temporary lake is superimposed on the original jökulhlaup. Deposits associated with lake-basin retro-,lling have a long-term preservation potential that could help to identify temporary ice-dammed lake formation in modern and ancient glacial environments. Copyright © 2003 John Wiley & Sons, Ltd. [source] Minor and trace element export from a glacierized Alpine headwater catchment (Haut Glacier d'Arolla, Switzerland)HYDROLOGICAL PROCESSES, Issue 18 2001Andrew Mitchell Abstract Major ion concentrations in meltwaters draining glacial environments have been widely reported. However, concentrations of minor and trace elements have received scant attention. This study presents trace and minor element variations in bulk meltwaters draining Haut Glacier d'Arolla (Switzerland) based on twice-daily sampling throughout the 1999 ablation season, which represents the most detailed meltwater quality dataset to date. In order to assess the mode of export from the catchment, these elements are partitioned into (i) ,dissolved' and (ii) ,particulate-associated' minor and trace element components. A computer-based speciation model (PHREEQCi) was applied to the bulk meltwater data, suggesting that Ba, Be, Cd, Cu, Li, Rb and Sr exist primarily as mobile monovalent or divalent dissolved cations, which may be involved in interactions with suspended sediment surfaces. Conversely, the model predicts the precipitation of Fe, Al, Mn and Cr (oxi)hydroxides, suggesting these species may be predominantly transported as colloids, which may remove other minor and trace elements from solution by co-precipitation reactions. Laboratory leaching experiments on suspended sediments and fresh rock powder suggests that minor and trace element concentrations may also be influenced by (oxy)hydroxide precipitation and adsorption,desorption reactions with suspended sediment surfaces. The quantity and transport mode of trace and minor elements may influence their bioavailability downstream of glacierized headwater catchments. Further, the enrichment of many dissolved minor and trace elements in meltwaters compared with world stream-waters, coupled with the timing of water and sediment delivery during the summer months, may have implications for downstream aquatic environments. Copyright © 2001 John Wiley & Sons, Ltd. [source] Glaciomarine deposition around the Irish Sea basin: some problems and solutionsJOURNAL OF QUATERNARY SCIENCE, Issue 5 2001Dr. Jasper Knight Abstract Reconstructing the depositional processes and setting (marine or terrestrial depositional environment) of late Devensian age glacigenic sediments around the Irish Sea basin (ISB) is critical for developing an all-embracing and consistent glacial model that can account for all observed field evidence. Identifying episodes of marine and terrestrial glacial deposition from field data is considered the first step in achieving this goal. Criteria for distinguishing marine and terrestrial glacial environments in the ISB include the geomorphology, sedimentology and faunal content (biofacies) of the associated deposits. Exposures of glacigenic sediments around the ISB are very diverse in terms of their morphosedimentary characteristics and associated biofacies, and thus inferred depositional processes and setting. Possible reasons for the diverse geological record include the differing geometry of eastern and western ISB coasts, time-transgressive ice retreat, and differential land rebound effects as a result of forebulge collapse and neotectonics. Poor geochronometric control on ice sheet events has not helped the correlation of ISB events with glacial and climatic events elsewhere. Future investigations of glacial sites around the ISB should use an integrated methodological approach involving a range of geomorphological, sedimentary and biofacies data, and dating control where possible. This will help in developing a more precise and holistic late Devensian glacial model that is constrained rigorously by field geological evidence. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||