RECENT ADVANCE AND RETREAT OF THE LAND LOBE GLACIER, COLUMBIA BAY, SOUTHCENTRAL ALASKA

The Land Lobe, a distributary of the Columbia Glacier, extends 5 km to a terminus just above that of this large tidewater glacier. Although sharing the same accumulation area, the Land Lobe has retreated only a few kilometers in the last century compared with 12 km since 1982 for the trunk glacier.

The retreat of both glaciers has uncovered thousands of mountain hemlock logs from forests previously overrun by expanding ice margins. From logs on the Land Lobe forefield, 95 tree cores have been recovered from 11 sites. Calendar dates from these reveal continuous advance occurred from 1780 through 1860 just before termination near the present snout. These data suggest advance rates of 3-10 m/yr for the Land Lobe compared with rates of 20-30 m/yr estimated in a similar manner for the adjacent trunk of Columbia Glacier. Comparisons of the glacier record with tree-ring-based proxy temperature data from the area, indicate that glacier expansions have been relatively insensitive to changing temperature on the scale of multi-decadal variations and appear to integrate longer, century-scale coolings. The persistent advance of the Land Lobe over the reconstructed 100-yr period, is consistent with a similarly reconstructed recent advance history from the fjord. These results seem to confirm that the chronology of the Land Lobe is dominated by the mass balance and dynamics of the trunk glacier.