UMass Amherst GEO-SCI 563 - Role Of Water (9 pages)

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Role Of Water



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Role Of Water

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Pages:
9
School:
University of Massachusetts Amherst
Course:
Geo-Sci 563 - Glacial Geology
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9 29 09 The Role of Water in Glaciofluvial Systems Readings Glacial Dirt Machine Vs Analogs with the Malaspina Glacier Conduits and Conditions for lubrication and phase change through Regelation Or Water Runs Through it A Recipe for more work Sept 29 2009 Glacier Velocities Us Water in Glaciers Supraglacial water Valley Glaciers 3 200 or 300 m yr Ice Sheets 3 250 m yr Ice Streams w in ice sheets 1 km yr Surging Glaciers 1 7 km yr Eg fastest glacier Jakobshaven Isbrae now 14 km yr was 8 4 km yr Ice Stream B Whillians Ice Stream 800 m yr Surface lakes episodic draining Surface Streams enters englacial and subglacial system via moulins crevasses etc forms karst like networks larger seasonal changes in volume entrains material and flushes to outwash areas 1 9 29 09 Water in Glaciers Englacial water within the ice Under pressure due to confining pressure of the ice and closing off of conduits by creep Balance between melt back and creep Cavities and conduits can form 3 D gallery Studied using dyes Open due to thermal energy Rothlisberger channels R channels Water in Glaciers Subglacial water Sheet flow water layers Weertman films can drown obstacles reduce friction Channel flow cavities channels conduits R N C channels Interstitial water in sediments Linked cavities Nye Channels N channels Water Films Braided channels Pics from Bill Locke Univ Montana 2 9 29 09 Water flows from regions of high hydraulic potential to areas of low hydraulic potential Cartoon x section of ice sheet follows the steepest hydraulic gradient perpendicular to lines of equipotential Balance of elevation and pressure Ice surfa ce ce tial surfa Equipoten A Level surface C B Water filled tube Zwally effect does matter to ice sheet future Parizek Alley 2004 Das et al 2008 Science o Investigated hydro fractures thru 1 km thick ice o Instrumented 2 surface lakes o One lake drained in 2 hrs down 980 m to bed by water driven fracture proagation evolving into a moulin o Coincided with increased seismicity accelerated flow ice sheet uplift o Peak flow exceeded that over Niagara Falls o Next 24 hrs saw subsidence and deceleration o Confirms theoretical predictions of hydro fracturing in cold ice o Speed up not radical in the outlet glaciers http bigice apl washington edu projects greenlandlakes html Wt of ice above A is to elevation of the water column BC thinner ice above A is less hydraulic head BC Hydraulic head or potential falls toward the ice margin 3 9 29 09 http bigice apl washington edu index html http bigice apl washington edu Case in point Jakobshavn Glacier speedup from ice shelf collapse 1992 2000 Joughin et al Nature 2004 Jakobshavn Glacier blue line indicates the calving front in 1942 followed by the subsequent recession in 2001 orange 2002 yellow and 2003 red Left image showing the flow of glacial ice toward the ocean was derived from ERS SAR measurements The flow rate more than doubled over the period from 1997 to 2003 http svs gsfc nasa gov vis 4 9 29 09 Rock Floating ice mess Berg Ice Flow Slowed a little then sped up a lot Rock Jakobshavn Isbrae W Greenland Retreat with acceleration after ice shelf loss likely caused by warming Image courtesy Ian Joughin Alley et al submitted Blue slow thickening Red yellow fast thinning Numbers around coast warming mid 1990s and more recently vs previous Krabill et al 2004 GRL Inland thickening from increased snowfall coastal thinning from increased melting and also from dynamical response to increased melting Warming occurring and all changes consistent with warming Net is thinning contributing to sea level rise Joughin et al 2004 Jakobshavn is speeding up Zwally et al Science 2002 Greenland ice accelerates More speed up with more melt when melt starts 5 9 29 09 Ice Shelf http bprc osu edu rsl radarsat radarsat html Fast velocities Fast sliding not Fast creep http nsidc org data velmap siple streamb streamb html RADARSAT SAR imagery obtained during the 1997 Antarctic Mapping Mission upstream velocity of the Recovery Glacier is about 100 meters year light blue areas Near the grounding line there is a local peak velocity of about 900 meters year yellow and red areas 6 9 29 09 Flicker et al Science 15 Feb 2007 Provides the first evidence that subglacial water is stored in a linked system of reservoirs underneath the ice can move quickly into and out of those reservoirs This activity may play a major role in controlling the rate at which ice moves off the continent Comparisons of elevation profiles taken by altimetry instruments on NASA s Ice Cloud and land Elevation Satellite ICESat revealed the draining of a subglacial lake some 1 km 3 290 feet beneath the ice with an area of about 10 km by 30 km 6 x 18 5 miles Total water volume loss was about 2 km3 5 28 1011 US gallons to the ocean under the Ross Ice Shelf through a subglacial channel The Labyrinth Channel Network Subglacial Hydrology subglacial floods Timeline for Victoria Land subglacial floods Cold based alpine glaciation Hyper arid cold polar desert Convoy Potholes and Landscape 10 Ma Asgard till Koenig colluvium Thermal transition Ice expansion Subglacial floods 14 8 13 6 Ma mid Miocene Sessrumnir till 1m Ar dating 15 Ma Temperatestyle glaciation wet based Lewis et al in press Marchant et al Tundra vegetation Marchant et al 7 9 29 09 Subglacial dissolution Saturation of well aerated water makes carbonic acid CO2 H2O H2CO3 So CaCO3 H2CO3 Ca 2 2HCO3 Ice marginal lakes Can be important way to recreate outburst floods or Jokalups Can repeat often dissolution precipitation Dissolves limestone and marble can also precipitate spicules and coatings Regelation can cause precipitation 8 9 29 09 Scablands Missoula Floods Repeating 55 year cycle of flooding and lake refill from 15 13 ka could be 25 massive floods J Connor and G Benito Shorelines Angela Brown about com J Harlen Bretz in 1949 9


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