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

目前关于冰川如何响应由气候引起的物质平衡变化的理论理解是基于运动波的传播和扩散，这是由奈提出的，并在最近的地质文献中进行了回顾。将这一理论应用于若干冰川实例表明，一个典型的冰川需要几百年才能完成对气候变化的响应。然而，关于“小冰期”期间及之后冰川波动的现有证据表明，响应时间比这一预测短得多。根据理论分析，之所以出现这种差异，是因为理论模型预测的冰体积变化比实际大了一个数量级以上。对体积变化的过高估计是由于假设波速和扩散系数在终端区附近如何变化，从而导致对终端区的厚度变化以及厚度变化如何沿冰川长度扩散的过高估计。该项目将检查实际前进和后退冰川的高程变化剖面图，以便将体积变化与长度变化联系起来。在过去的几十年里，主要来自阿尔卑斯山和华盛顿的冰川剖面变化的顺序调查数据，以及在更长的时间尺度上由选定冰川的侧冰碛和修剪线记录的净高程变化的地貌证据，将被使用。这些测量将有助于描述和理解“小冰期”侧冰碛和修剪线与当前冰川表面的关系。“小冰期”和当前冰川边缘的上向辐合是目前山地景观的一个众所周知的特征，但尚未得到系统的研究。这种模式的定量方面与气候调整的响应时间密切相关，因此对古气候解释有重要影响，并增加了我们对冰川行为的理解。

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.