Thickness change and flow of Tyndall Glacier, Patagonia

In December 1993, we measured surface elevations and ice flow-velocities in the upper part of the ablation area of Tyndall Glacier, southern Patagonia. The measuring points were almost same as those in previous measurements in 1990. Comparing the results with those in 1990 and in 1985, we estimated average annual change of the surface elevation between 1990 and 1993 to be -3.1 m/a, which was close to that between 1985 and 1990 of -4.0 m/a. Therefore, we see that this part of the glacier has been thinning continuously during the last eight years. The rate is large compared to other retreating glaciers in the world. Flow velocities obtained by the measurements at an interval of nine days were 0.065 m/day to 0.61 m/day near the eastern margin. They were larger than those obtained in December 1990. Displacements of painted stones which were left on the glacier surface in 1990 gave annual flow velocities of 16.6 m/a to 47.3 m/a. From measurements of a strain grid, annual emergence velocity was estimated to be about 10 m and a brief discussion on mass balance was made.