Asynchronous Maximum Advances of Mountain and Continental Glaciers

The last maximum glacier advance in many mountain ranges appears to have predated the last maximum advance of the Wisconsinan continental ice sheets (-20,000 years B.P.). Published evidence from widely spaced localities in North and South America, Europe, Asia, and Hawai'i suggests that some mountain glaciers extended farther during one or more stades early in the last glaciation, roughly 115,000-30,000 years B.P., than at its end, when low global temperature and high precipitation presumably were most favorable for the growth of glaciers. Variations in the timing of glacier advances in different mountain ranges suggest that alpine glaciers are dependent on regional climate as well as global conditions. Their study might provide sensitive tests for theories of global climate change. Glacial deposits are often used as time markers in neotectonic and geomorphic studies, and their ages sometimes are inferred from distant measurements or from proxy histories of global climate change. Undated geomorphic features such as moraines, sharply incised streams, and river terraces, which commonly have been associated with the last maximum glacier advance (-20,000 years B.P.) or last deglaciation (-13,000 years B.P.), may actually be older by a factor of 2 to 4 (or more). Conversely, deposits assigned to the maximum advances of the penultimate global glaciation (—130,000 years B.P.) may actually date from early in the most recent glacial cycle and be younger by a comparable factor. Rates of faulting or folding estimated from displacements or deformation and the assumed ages of such geomorphic features might be too great (or too small) by corresponding factors.