This figure shows an image map of three ICESat/GLAS tracks from the eight-day missions that were used to investigate the response of Hektoria Glacier in the Antarctic Peninsula to the loss of the Larsen B Ice Shelf in March of 2002. The three tracks cross the lower portion of the glacier at an angle. In dark blue are contours showing the level of speed increase in meters per day since breakup of the shelf.

Laser points were compared along the ice flow direction (indicated by light blue lines). As the bottom graph shows, the third, middle GLAS track indicated surface elevations far below those expected from interpolation between the first two tracks. The estimate was iterated twice to account for probable lowering between the first two outer tracks.

The three 2003 tracks indicate lowerings of between 5 and 38 m over a period of just six months, a dramatic signal indicating major changes in the forces controlling ice flow. The amount of lowering correlates with slope. Overall, the speed and drawdown data indicate that loss of the ice shelf initiated a significant increase in slope of the glacier surface, causing it to accelerate and thicken.

The GLAS instrument precision during the eight-day repeat data was somewhat lower than for later data, estimated at about 50cm. However, the main error in the glacier slope measurement here comes from the along-flow interpolation. Using surface roughness of the two early tracks as a guide, the error in the interpolation is estimated at ± 6 m.

Citation

Scambos, T. A., J. Bohlander, C. Shuman, and P. Skvarka, 2004. Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica. Geophysical Research Letters. In press.