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Tidal Modulation of Stick-Slip Ice Stream Motion

Update. Tidal Modulation of Stick-Slip Ice Stream Motion. R. A. Bindschadler M.King P. Vornberger S. Anandakrishnan I. Joughin D. Voigt R. A. Alley. We acknowledge NSF OPP for their financial and logistic support. Old. 2003-2004 Field Season. 21 GPS stations

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Tidal Modulation of Stick-Slip Ice Stream Motion

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  1. Update Tidal Modulation of Stick-Slip Ice Stream Motion R. A. Bindschadler M.King P. Vornberger S. Anandakrishnan I. Joughin D. Voigt R. A. Alley We acknowledge NSF OPP for their financial and logistic support

  2. Old 2003-2004 Field Season • 21 GPS stations • 5 reference (for differential sol’n) • 4 floating (for tides) • 15 sec. sampling • 7 seismic networks (triggered) • 1 tiltmeter • 1 winterover station 70+ DAYS OF DATA

  3. Old Whillans Ice Stream Stick-slip Only Ross ice stream that exhibits stick slip 5 min positions B010

  4. Update Spring and NeapTides 73-day record has multiple spring-neap cycles Spring tide intervals (shaded) defined as cycles of single component and high amplitude tide

  5. 138 events picked from 30-min. running avg. • ~12-hr intervals defined by midpoints between events Update Event and Interval Definition

  6. Slip vs. Total Motion Update ~90% of motion occurs during slip events High position errors

  7. Update Spring vs. Neap Speed ~15% faster during spring tides

  8. Old Tidal Correlation • Maximum 5-min displacement correlates with tidal magnitude (spring vs. neap) Motion BFLT Tide B010 BFLT

  9. Slip Characteristics Position 12 hour total 30 minute slip slope= max. speed Time

  10. Update Spring vs. Neap Slips Position Spring tide slip Higher average speed during spring tides Higher maximum speed Neaptide slip Time

  11. Update Actual example Spring slip Neap slip

  12. B320 B190 B140 B090 B010 BFLT Old Preliminary Findings • Maximum slip magnitude decreases upstream • Tidal modulation occurs at least as far upstream as B190 Increasing upstream distance

  13. How does B090 compare with B010? B090 B010 BFLT

  14. Slip vs. Total Motion (B090) High position errors Update ~70% of B090 motion occurs during slip events (90% for B010)

  15. Update Spring vs. Neap Speed (B090) ~6% faster during spring tides (15% for B010)

  16. Update Event propagation Longer delays during neap tide

  17. Update Slip Origin? B140 B190 B090 B010

  18. Old Simple Stick-slip Model Ice stream pushes Tide resists Stress drop = .3 kPa H = 750 m L = 100 km tyield = 4 kPa

  19. Model has the form k/g is relative importance of ice stream loading vs. tidal influence Can examine stress buildup between events to find temporal variation of stress drop for each event and relative strength of ice stream loading Update Re-examine Model Parameters

  20. Previously: Stress drop = 0.3 F = .51 Revised: Stress drop = 0.25 F = .49

  21. model observation Update Model Prediction Spacing is generally correct, but timing is sometimes wrong

  22. Next field season (2004-2005) Detailed study of Whillans Ice Stream 30+ GPS sites Seismic experiments on ice plain Final field season (2005-2006) Detailed study of Ice Stream D 2003-2004 Both seasons 2004-2005 Continuing Research • Examine 2003-2004 data from other Whillans Ice Stream sites

  23. Update Conclusions • Whillans Ice Stream is the only Ross ice stream that exhibits stick-slip motion • Slip origins appear to have a persistent location at or near north margin • Slip accounts for majority of motion • ~90% at B010; ~70% at B090 • Spring-tide speed faster than neap-tide speed • ~15% faster at B010; ~6% faster at B090 • Spring-tide slips more impulsive than neap-tide slips

  24. Thank you

  25. Outline • Only Whillans Ice Stream • Further characteristics of stick-slip motion

  26. Ross Ice Streams A Transantarctic Mountains Whillans Byrd C Crary Ice Rise D Siple Dome Ross Ice Shelf E Roosevelt Island

  27. B320 B190 B140 B090 B010 BFLT Old Preliminary Findings • Timing • Slips not evident at B320 • Events occur at very similar times • Events take <15 minutes to propagate to all stations • Slips last 5-20 minutes Increasing upstream distance Slip Initiation Floating site

  28. Movie of Stick-Slip Events

  29. (tyield – to) HV E = P L2 2 E: Young’s Modulus h: tide amplitude: 1 meter =10 kPa stress to : minimum basal stress : stored elastic strain H = 750 m L = 100 km tyield = 4 kPa Calculate stress drop where 2 events per tidal period, P Old Simple Stick-slip Model Ice Stream pushes

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