Time Scales for Advance and Retreat of Glaciers in Response to Climate Changes

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Current theoretical understanding of how glaciers respond to changes in mass balance induced by climate is based on the propagation and diffusion of kinematic waves as developed by Nye and reviewed in the most recent geological texts. Application of this theory to several example glaciers indicates that it should take several hundred years for a typical glacier to complete its response to a change in climate. However, available evidence about glacier fluctuations during the "Little Ice Age" and subsequently indicates response times much shorter than this prediction. Based on theoretical analysis, the discrepancy arises because the ice volume changes predicted by the theoretical models are unrealistically large by up to more than one order of magnitude. The over estimate of volume change arises from assumptions about how wave velocity and diffusion coefficients vary near the terminus, which cause over estimate of thickness change in the terminal zone and how the thickness change is spread up the glacier length. This project will examine elevation change profiles on actual advancing and retreating glaciers in order to relate volume changes to changes in length. Available sequential survey data of profile changes over the last several decades on glaciers primarily from the Alps and Washington will be used as well as geomorphic evidence for net elevation changes on longer time scales as recorded by lateral moraines and trim lines on selected glaciers. These measurements will contribute to a description and understanding of the relationship of "Little Ice Age" lateral moraines and trim lines to current glacier surfaces. The up valley convergence of "Little Ice Age" and current glacier margins is a well known feature of the present mountain landscape which has not been systematically investigated. The quantitative aspects of this pattern are intimately tied to the response time for adjustment to climate, thereby having significant bearing on paleoclimatic interpretation and adding to our understanding of the behavior of glacier.