HR: 14:00h
AN: NS43A-03 INVITED     [Abstracts]
TI: Application of Near-Surface Geophysics to Problems in Glacier Dynamics, Pitted Outwash Plain Formation, and Glaciotectonics, Matanuska Glacier, Alaska
AU: * Baker, G S
EM: gbaker@geology.buffalo.edu
AF: University at Buffalo, Department of Geology 876 Natural Sciences Complex Buffalo, NY 14260, Buffalo, NY 14260 United States
AU: Pyke, K
EM: pyke10@geology.ohio-state.edu
AF: Ohio State, College of Math and Physical Sciences 374 Mendenhall, Columbus, OH 43210 United States
AU: Evenson, E
EM: ebe0@lehigh.edu
AF: Lehigh University, Dept. of Earth and Environmental Sciences, Bethlehem, PA United States
AU: Lawson, D
EM: Daniel.E.Lawson@erdc.usace.army.mil
AF: USA-CRREL, 72 Lyme Road, Hanover, NH 03755 United States
AU: Larson, G
EM: larsong@msu.edu
AF: Michigan State, Dept. of Geological Sciences, East Lansing, MI United States
AU: Alley, R B
EM: rba6@psu.edu
AF: Penn State, Earth and Mineral Science, University Park, PA 16802 United States
AB: From 2000 to 2004, near-surface geophysics data in various forms was collected near the active terminus of Matanuska Glacier, Alaska, to address several specific hypotheses and also provide general subsurface information in several relatively unsampled zones of the subsurface. (1) Seismic reflection data was collected on the glacier to test the predicted thickening of debris-rich basal ice in response to the motion of the glacier out of a localized overdeepening. The seismic data imaged the 5-to-10 meter thick basal ice at depths of 50-150 m, and clearly showed a 50 percent thicking--supporting the glaciohydraulic supercooling mechanism for basal ice formation. An interesting result of this basal-freeze-on mechanism of forced equilibrium is the concept of the "graded glacier" that has implications of sediment-pumping effects in response to changes in the surface slope of the glacier in response to climate change. (2) Seismic reflection, GPR, and electrical resistivity data were collected in a proximal pitted outwash plain abutting the active margin of Matanuska Glacier. These data indicate the presence of laterally continuous "slabs" of buried ice, in places possibly in duplex-like structures formed during readvances. The formation of thermokarst resulting in pits (sinkholes) in the surface of the outwash plain are therefore interpreted to result from preferential pathways of melting (relict moulins?) in the buried ice slabs, rather than from discreet blocks of ice. (3) 4-D GPR data (3-D through time) were collected at the terminus of Matanuska Glacier in an attempt to examine the formation of debris-flow-generated stratigraphy during the collapse of a portion of an ice-cored moraine complex. During a 30-m readvance of the glacier (2002-2003, between "snapshots" of data collection) glaciotectonic deformation of the moraine stratigraphy was observed. The GPR data indicate that the readvancing glacier impacted the rigid buried ice within the moraine, passively translating and deforming the overlying sediment in response to occasional brittle faulting and thrusting of the buried ice.
DE: 1630 Impact phenomena
DE: 1694 Instruments and techniques
DE: 1823 Frozen ground
DE: 1863 Snow and ice (1827)
DE: 5199 General or miscellaneous
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly