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

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

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

Wind River, WyomingWind River, Wyoming

Meandering river over permafrost, AlaskaMeandering river over permafrost, Alaska

San Juan River, UtahSan Juan River, Utah

Meanders on Meanders on Mars

GreenlandGreenland

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

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

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

Each day a longitudinal groove forms in the channel caused by diurnal variations in

stream width

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

Objective of study was to describe & explain rate & direction of meander migration in supraglacial streams

Near C-29, Cathedral Glacier

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

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

Meander #2 P = 1.07 r/W = 9.2

Meander #4 P = 1.22 r/W = 3.0

Meander #6 P = 1.32 r/W = 6.3

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

Results

Rio Negro, Patagonia, Rio Negro, Patagonia, ArgentinaArgentina