meander migration in supraglacial streams, juneau icefield, alaska richard a. marston kansas state...
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Meander Migration in Supraglacial Streams, Juneau Icefield, Alaska
Richard A. Marston Kansas State University Jefferson Science Fellow
National Academies and U.S. Department of State, Office of
The Geographer and Global Issues
Inci Guneralp Texas A&M University
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4000 km2 of sub-polar ice in Boundary Coast Range of AK-BC
30 outlet glaciers from high plateau of ice at 1400 m
Supraglacial stream research at confluence of Vaughan Lewis and Gilkey glaciers at 1100 m elevation
Research supported by FGER, NSF-REU
Juneau Icefield
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The rates and directions of meander migration remain poorly understood
Could study with… historical aerial
photos, maps, field surveys
lab simulations with stream tables
Landsat: MississippiRiver, AR-MS
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Wind River, WyomingWind River, Wyoming
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Meandering river over permafrost, AlaskaMeandering river over permafrost, Alaska
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San Juan River, UtahSan Juan River, Utah
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Meanders on Meanders on Mars
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GreenlandGreenland
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Use supraglacial streams as an analogue
Best formed in firn below the transient snowline
Must downcut faster than glacier surface ablation
Few crevasses
Near C-18B, Gilkey Glacier-Vaughan Lewis Glacier convergence zone
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Supraglacial streams
Time & scale not important in meander development
Sediment load not necessary to initiate meanders but clastics do alter meander dimensions
Super-elevation of water surface against outer bank could provide the incremental frictional heat for differential thermal erosion
Near C-29, Cathedral Glacier
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SG streams similar to incised meanders Meanders migrate
simultaneous with downcutting
SG streams similar to meanders cut in alluvium with high %clay-silt Hydraulic geometry Unit stream power vs. sinuosity Discharge vs. meander
wavelength Channel width vs. meander
wavelength
Near C-18B, Vaughan Lewis Glacier
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Each day a longitudinal groove forms in the channel caused by diurnal variations in
stream width
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Simultaneous with downcutting and formation of daily grooves, SG meanders migrate by translation and extension 3-D record of meander position
Near C18B, Vaughan Lewis Glacier
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Objective of study was to describe & explain rate & direction of meander migration in supraglacial streams
Near C-29, Cathedral Glacier
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Field Methods1) measure geometry for 6 meanders2) track daily change in position of apex of each meander3) measure peak Q and distribution of shear stress in each bend
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Supraglacial stream dimensionsWidth (W) ranged from 18-120cmSinuosity (P) ranged from 1.07-1.67Channel curvature (r/W) ranged from 1.8-9.2Peak discharge (Qp) ranged from 20-240 l/s
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Meander #2 P = 1.07 r/W = 9.2
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Meander #4 P = 1.22 r/W = 3.0
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Meander #6 P = 1.32 r/W = 6.3
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Results
• Extension is more important than translation in meanders with high P, low r/W, low Qp (e.g., meander #6)
• Translation dominate over extension in meanders with low P, high r/W, high Qp (e.g., meander #4)
• Extension and translation both increase as Qp increases
• Total rates of migration = 8 to 77 cm/d
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Results
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Rio Negro, Patagonia, Rio Negro, Patagonia, ArgentinaArgentina
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