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Sediment sources and transport by the Kahiltna Glacier and other catchments along the south side of the Alaska Range, Alaska

A. Matmon and P. J. Haeussler
Sediment sources and transport by the Kahiltna Glacier and other catchments along the south side of the Alaska Range, Alaska
Geosphere (Boulder, CO) (March 2020) 16 (3): 787-805

Abstract

Erosion related to glacial activity produces enormous amounts of sediment. However, sediment mobilization in glacial systems is extremely complex. Sediment is derived from headwalls, slopes along the margins of glaciers, and basal erosion; however, the rates and relative contributions of each are unknown. To test and quantify conceptual models for sediment generation and transport in a simple valley glacier system, we collected samples for (super 10) Be analysis from the Kahiltna Glacier, which flows off Denali, the tallest mountain in North America. We collected angular quartz clasts on bedrock ledges from a high mountainside above the equilibrium line altitude (ELA), amalgamated clast samples from medial moraines, and sand samples from the river below the glacier. We also collected sand from nine other rivers along the south flank of the Alaska Range. In the upper catchment of the Kahiltna drainage system, toppling, rockfall, and slab collapse are significant erosional processes. Erosion rates of hundreds of millimeters per thousand years were calculated from (super 10) Be concentrations. The (super 10) Be concentrations in amalgamated samples from medial moraines showed concentrations much lower than those measured from the high mountainside, a result of the incorporation of thick, and effectively unexposed, blocks into the moraine, as well as the incorporation of material from lower-elevation nearby slopes above the moraines. The (super 10) Be sediment samples from downstream of the Kahiltna Glacier terminus showed decreasing concentrations with increasing distance from the moraine, indicating the incorporation of material that was less exposed to cosmic rays, most likely from the glacier base as well as from slopes downstream of the glacier. Taken together, (super 10) Be concentrations in various samples from the Kahiltna drainage system indicated erosion rates of hundreds of millimeters per thousand years, which is typical of tectonically active terrains. We also measured (super 10) Be concentrations from river sediment samples collected from across the south flank of the Alaska Range. Calculation of basinwide weighted erosion rates that incorporated hypsometric curves produced unrealistically high erosion rates, which indicates that the major source of sediment was not exposed to cosmic rays and was primarily derived from the base of glaciers. Moreover, the apparently high erosion rates suggest that parts of each drainage system are not in erosional steady state with respect to cosmogenic isotope accumulation.


EISSN: 1553-040X
Serial Title: Geosphere (Boulder, CO)
Serial Volume: 16
Serial Issue: 3
Title: Sediment sources and transport by the Kahiltna Glacier and other catchments along the south side of the Alaska Range, Alaska
Affiliation: Hebrew University of Jerusalem, Institute of Earth Sciences, Jerusalem, Israel
Affiliation: Republique Francaise, Centre de Recherche et d'Enseignement de Geosciences de l'Environnement, ASTER TeamAix-en-ProvenceFrance
Pages: 787-805
Published: 20200310
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 68
Accession Number: 2020-028710
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, geol. sketch map
N62°00'00" - N63°00'00", W152°00'00" - W145°00'00"
Secondary Affiliation: U. S. Geological Survey, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 202019
Program Name: USGSOPNon-USGS publications with USGS authors
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