NASA ICESat/GLAS tracks over Hektoria Glacier, Antarctica
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.
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.