29 september 2009wais/pack forest conference center variation in subglacial roughness in west...

29 September 2009 WAIS/Pack Forest Conference Center

Variation in Subglacial Roughness in West Antarctica: How do we interpret causality in

the context of sediments?Young, D. A., D.D. Blankenship, S.D. Kempf, J.B.

DeSantos, M. Williams, and J. W. Holt


AIry isostatic deglaciated coastline [Holt et al., 2006]


50x vertical50x vertical

Thwaites GlacierThwaites Glacier

Grounding lineGrounding line

MacAyeal Ice Stream (Ice Stream E)MacAyeal Ice Stream (Ice Stream E)

Grounding lineGrounding line


Is it the smoothness (symptomatic of smaller scales) that allows rapid basal motion;or is it the rapid basal motion that has

smoothed the topography?


Basal shear stress inversion [Joughin et al., 2009; 2004]


Density variations not due to topography or crustal thickness

Lower values imply sediment

Isostatic anomaly [Diehl et al., ISASE X 2007]

Airborne gravity data


Anomaly of residual intensity [Holt et al., ISASE X 2007]

Lower values imply sediment cover (or sedimentary basement)

Airborne magnetic data


Estimating RMS slope:

detrend


Estimating RMS slope:

calculate slope and bin


Across trackAlong track

(with focusing)

Peters et al. 2007 IEEE

60 MHz beam pattern


Second Across track Null


King et al, 2009 result for Rutford


Rignot et al, 2005


Anisotropic observations - implies topographic

features

Rignot et al, 2005


Basal shear stressJoughin et al, 2009


2000 meter deviation


40 meter deviation


Conclusions

Low driving stress regions of Thwaites Glacier, MacAyeal Ice Stream and Kamb Ice

Stream are underlain by topographic lineations largely confined to the smooth

material

Low driving stress regions in the WAIS correlate with smooth (at 10’s-100‘s m)

material

This is consistent with a deforming reservoir of till; of which Thwaites

Glacier is lacking.

Thanks to G. Unger Vetlesen Foundation the University of Texas at Austin Jackson School of Geoscience, NASA, and the National

Science Foundation (OPP projects 0230197, 9319379,0086316, 9911617, 9120464, 9319369)

ICECAP


Budd Basin

WAIS/Pack Forest Conference Center

ICECAP


29 september 2009wais/pack forest conference center variation in subglacial roughness in west...

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