GLACIOISOSTASY AND LAKE-LEVEL CHANGE AT MOOSEHEAD LAKE, MAINE

Reconstructions of glacioisostatic rebound based on relative sea level in Maine and adjacent Canada do not agree well with existing geophysi cal models. In order to understand these discrepancies better, we inve stigated the lake-level history of 40-km-long Moosehead Lake in northw estern Maine. Glacioisostasy has affected the level of Moosehead Lake since deglaciation ca. 12,500 C-14 yr B.P. Lowstand features at the so utheastern end and an abandoned outlet at the northwestern end of the lake indicate that the lake basin was tilted down to the northwest, to ward the retreating ice sheet, by 0.7 m/km at 10,000 C-14 yr B.P. Wate r level then rose rapidly in the southeastern end of the lake, and the northwestern outlet was abandoned, indicating rapid relaxation of lan dscape tilt. Lowstand features at the northwestern end of the lake sug gest that the lake basin was tilted to the southeast at ca. 8750 C-14 yr B.P., possibly as the result of a migrating isostatic forebulge. Af ter 8000 C-14 yr B.P., water level at the southeastern end was again b elow present lake level and rose gradually thereafter. We found no evi dence suggesting that postglacial climate change significantly affecte d lake level. The rebound history inferred from lake-level data is con sistent with previous interpretations of nearby relative sealevel data , which indicate a significantly steeper and faster-moving ice-proxima l depression and ice-distal forebulge than geophysical models predict. (C) 1998 University of Washington.