A mini-surge on the Ryder Glacier, Greenland, observed by satellite radar interferometry

Science

Volumn 274, Issue 5285, 1996, Pages 228-230

  Joughin, Ian ^a   Tulaczyk, Slawek ^b   Fahnestock, Mark ^c   Kwok, Ron ^a  

^a CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

^b CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

^c UNIVERSITY OF MARYLAND   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ICE;

ACCELERATION; ARTICLE; FLOW; GREENLAND; INTERFEROMETRY; LAKE; PRIORITY JOURNAL; SEASON; TELECOMMUNICATION; VELOCITY;

GLACIER FLOW; GLACIER SURGE; ICE SHEET; MELTWATER;

GREENLAND, RYDER GLACIER;

EID: 0029659907     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.274.5285.228     Document Type: Article

References (24)

1. K. Echelmeyer and W. Harrison [J. Glaciol. 36, 82 (1990)] looked for variation in the speed of Jakobshavns Isbrae, the fastest glacier in Greenland. Although they believed that there was a large seasonal input ot meltwater to the bed. their measurements exhibited no significant seasonal variation.
2. R. M. Goldstein, H. Engelhardt, B. Kamb, R. M. Frolich, Science 262, 1525 (1993).
3. I. Joughin, D. Winebrenner, M. Fahnestock. Geophys. Res. Lett. 22, 571 (1995).
4. E. Rignot, K. Jezek, H. Sohn, ibid., p. 575.
5. The term "mini-surge" was used by C. F. Raymond and S. Malone [J. Glaciol. 32, 178 (1986)] and B. Kamb and H, Engelhardt [ibid. 33, 27 (1987)] to describe pulses of high flow speed propagating down a valley glacier and related to basal water pressure. The event we observed occurred on a larger glacier, and we have no evidence for the propagation of a velocity pulse. The change in velocity was large and short-lived, thus matching several of the characteristics they observed. The Ryder speedup could be likened to a surge, but the event was too short to develop the changes in ice distribution characteristic of a surge.
6. The term "mini-surge" was used by C. F. Raymond and S. Malone [J. Glaciol. 32, 178 (1986)] and B. Kamb and H, Engelhardt [ibid. 33, 27 (1987)] to describe pulses of high flow speed propagating down a valley glacier and related to basal water pressure. The event we observed occurred on a larger glacier, and we have no evidence for the propagation of a velocity pulse. The change in velocity was large and short-lived, thus matching several of the characteristics they observed. The Ryder speedup could be likened to a surge, but the event was too short to develop the changes in ice distribution characteristic of a surge.
7. J. G. Ferrigno et al., Ann. Glaciol. 17, 239 (1993).
8. M. Meier et al., J. Geophys. Res. 99, 15219 (1994).
9. B. Kamb et al., Science 227, 469 (1985).
10. Basin-wide accumulation was derived from data published by A. Ohmura and N. Reeh [J. Glaciol. 37, 140 (1991)].
11. R. Goldstein, Geophys. Res. Lett. 22, 2517 (1995).
12. Velocity differences below 150 m/year are accurate to within about 10 m/year. Where we measured larger differences, the errors may be greater because of proximity to regions where the phase could not be unwrapped (that is, have the modulo-2π ambiguity removed).
13. Over large parts of the fast-moving areas, fringes remain visible but are too noisy to unwrap.
14. For equal flow rates, the pattern of fringes is three times denser for a 3-day versus a 1-day interferogram, because three times the displacement occurred. Where we could not estimate velocity, the noisy fringe patterns for the 1-day October interferogram were visually denser than for the 3-day interferogram (acquired March 1992 and representative of the normal flow mode), suggesting that the October 1995 speed is in excess of three times its normal rate over some of the faster moving area.
15. The effect of vertical displacement, which is proportional to horizontal speed, dominates the phase at length scales of less than a few kilometers (3). Thus, similar short-scale variation observed in the November and September interferograms indicates that the horizontal speeds are comparable.
16. B. Kamb et al., J. Geophys. Res. 99, 15231 (1994).
17. Temporal decorrelation is caused by shifts in the relative positions of subpixel scatterers between acquisition of the images, which can be caused by rapid ice motion or the collapse of lake ice.
18. H. Thomsen, L. Thorning, R. Braithewaite, Geol. Surv. Greenland Nr. 738 (1985)
19. W. S. B. Paterson, The Physics of Glaciers (Pergamon, Oxford, ed. 2, 1994).
20. M. Fahnestock, R. Bindschadler, R. Kwok, K. Jezek, Science 262, 1530 (1993).
21. R. Kwok and M. Fahnestock, IEEE Trans. Geosci. Remote Sensing 34, 189 (1996); I. Joughin, D. Winebrenner, M. Fahnestock, R. Kwok, W. Krabill, J. Glaciol. 42, 10 (1996).
22. R. Kwok and M. Fahnestock, IEEE Trans. Geosci. Remote Sensing 34, 189 (1996); I. Joughin, D. Winebrenner, M. Fahnestock, R. Kwok, W. Krabill, J. Glaciol. 42, 10 (1996).
23. I. Joughin, R. Kwok, M. Fahnestock, J. Glaciol., in press.
24. We thank B. Bindschadler and the reviewers for their comments on the manuscript, and C. Wemer for providing the synthetic aperture radar processor. I.J. and R.K. performed this work at the Jet Propulsion Laboratory under contract with NASA. S.T. acknowledges support from the Henry and Grazyna Bauer fellowship. M.F. was supported under NASA Mission to Planet Earth grant NAGW4285. Radar data were supplied by the European Space Agency.