Morphological dynamics of an englacial channel
| Autor: | Geir Vatne, Tristram Irvine-Fynn |
|---|---|
| Rok vydání: | 2016 |
| Předmět: |
010504 meteorology & atmospheric sciences
Spatial organisation Flow (psychology) STREAMS 010502 geochemistry & geophysics lcsh:Technology 01 natural sciences lcsh:TD1-1066 Ice dynamics lcsh:Environmental technology. Sanitary engineering Meltwater Geomorphology lcsh:Environmental sciences 0105 earth and related environmental sciences General Environmental Science lcsh:GE1-350 geography geography.geographical_feature_category lcsh:T Moulin lcsh:Geography. Anthropology. Recreation Glacier lcsh:G General Earth and Planetary Sciences Geology Communication channel |
| Zdroj: | Hydrology and Earth System Sciences Hydrology and Earth System Sciences, Vol 20, Iss 7, Pp 2947-2964 (2016) |
| ISSN: | 1607-7938 |
| Popis: | Despite an interest in the hydraulic functioning of supraglacial and englacial channels over the last 4 decades, the processes and forms of such ice-bounded streams have remained poorly documented. Recent glaciological research has demonstrated the potential significance of so-called "cut-and-closure" streams, where englacial or subglacial flow paths are created from the long-term incision of supraglacial channels. These flow paths are reported to exhibit step-pool morphology, comprising knickpoints and/or knickzones, exaggerated in dimensions in comparison to supraglacial channels. However, little is known of the development of such channels' morphology. Here, we examine the spatial organisation of step pools and the upstream migration of steps, many of which form knickzones, with repeated surveys over a 10-year period in an englacial conduit in cold-based Austre Brøggerbreen, Svalbard. The observations show upstream step recession to be the dominant process for channel evolution. This is paralleled by an increase in average step height and conduit gradient over time. Characteristic channel-reach types and step-riser forms are consistently observed in each of the morphological surveys reported. We suggest that the formation of steps has a hydrodynamic origin, where step-pool geometry is more efficient for energy dissipation than meanders. The englacial channel system is one in rapid transition towards a quasi-equilibrium form within a decadal timescale. The evolution and recession of knickzones reported here result in the formation of a 37 m deep moulin shaft, suggesting that over time an incising supraglacial channel may evolve towards an englacial channel form exhibiting a stable end-point characterised by a singular vertical descent, which potentially can reach the glacier bed. This challenges the prevailing notions that crevasses or hydrofractures are needed to form deep moulins. Our observations highlight the need to further examine the adjustment processes in cut-and-closure channels to better understand their coupling to supraglacial meltwater sources and potential significance in cold-based glacier hydrology and ice dynamics. © Author(s) 2016. This work is distributed under the Creative Commons Attribution 3.0 License. CC-BY |
| Databáze: | OpenAIRE |
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