RUI: Paleohydrology of the Great Lakes region since the most recent glaciation

摘要自17000年前晚冰期以来，五大湖地区的水文特征发生了显著而剧烈的变化。大型前冰期湖泊突然干涸，地球缓慢的粘性变形导致出口垂直移动，影响了相关湖泊的水位。拟议的研究将使用地幔内粘性流动的数值模型来模拟地球固体表面相对于大地水准面的变形，这种变形是由上一个冰河时期冰荷载的变化引起的。古冰期和后冰期湖泊的岸线现在相对于现在的大地水准面倾斜，并提供随时间变化的地球变形数据。还将使用逆模型来预测与变形数据一致的冰盖厚度。这项研究的主要目标是模拟整个大湖地区在过去1.7万年中不断变化的水文性质。由于整个地区都有数字高程模型（DEM），因此对该地区各地的变形预测可以计算出古地形。通常使用地理信息系统（GIS）来确定给定当前地形（DEM）的现代河流网络。在拟议的工作中，地理信息系统将使用预测的古地形来确定综合河流系统和湖泊的水位，这些水位随着冰的退缩逐渐暴露出较低的出口和均衡隆起导致的出口高程变化而不断改变。在地理信息系统中，可以很容易地计算出冰川破裂时湖泊释放的淡水的确切体积。这样的估计很重要，因为影响海洋环流模式的冷淡水脉冲可能导致了极端快速的气候变化。地理信息系统还可以确定古流域和水系网络，并量化在任何时间、任何地点向任何河流提供地表水的总面积。海岸线的预测将被叠加在美国地质调查局的数字光栅图形地形图上，用于实地检查预测，这些预测将通过网站或cd向所有人提供。这些预测也可以下载到与全球定位系统（GPS）设备相连的掌上电脑上，用于在现场确定海岸线特征的准确位置，无论是预测还是观测。逆模型将根据数据调整冰盖历史和地球流变学。成功的反演将产生一个预测的冰盖厚度历史，有助于冰川学家和冰川地质学家试图了解劳伦泰德冰盖南部极限的动态性质。它还将有助于解决大湖区南部的地壳稳定性问题，并提高对该地区地球粘度结构和新构造的认识。这项研究将使地质学专业的本科生接触到数值模型、统计方法、先进的GIS实践和实地工作。他们继续积极参与美国地质学会的分会会议，并作为出版物的共同作者，这将刺激一个小型本科生地质系的研究环境，并鼓励本科生继续作为研究生院及以后的研究人员接受教育。

ABSTRACTThe Great Lakes region has experienced significant and dramatic changes in hydrologic character since late glacial times, 17,000 years ago. Large proglacial lakes drained suddenly and the slow viscous deformation of the earth caused outlets to move vertically affecting the associated lake levels. The proposed research will use a numerical model of viscous flow within the mantle to simulate deformation of the earth's solid surface relative to its geoid that was caused by the changing ice loads during the last ice age. Shorelines of the ancient glacial and postglacial lakes are now tilted relative to the present geoid and provide data of time-dependent earth deformation. An inverse model will also be used to predict the thickness of the ice sheets consistent with the deformation data.The main goal of the research is to simulate the changing hydrologic nature of the entire Great Lakes region during the past 17,000 years. Because digital elevation models (DEM's) exist over the entire region, predictions of deformation everywhere in the region allow calculation of paleo-topography. It is common to use geographic information systems (GIS) to determine modern stream networks given present topography (DEM's). In the proposed work, a GIS will use the predicted paleo-topography to determine the integrated river systems and lake levels that were continually modified as retreating ice exposed progressively lower outlets and as outlet elevation change resulted from isostatic uplift. Calculations are readily performed in the GIS of exact volumes of freshwater released by lakes as glacial burst events. Such estimates are important because cold freshwater pulses, affecting ocean circulation patterns, may have contributed to extremely rapid climate change. The GIS can also determine paleo- drainage basins and stream networks with quantification of the total area contributing surface water to any point on any stream and at any time.Predictions of shorelines will be superimposed upon USGS digital raster graphics topographic maps for use in field checking the predictions, and these predictions will be available to all on a website or CDs. The predictions can also be downloaded onto a handheld computer connected to a global positioning system (GPS) device and used to pinpoint in the field exact locations of shoreline features, whether predicted or observed. The inverse model will tune the ice sheet history and earth rheology to the data. Successful inversion will yield a predicted ice sheet thickness history helpful to glaciologists and glacial geologists attempting to understand the dynamic nature of the southern limit of the Laurentide ice sheet. It will also serve to address the issue of crustal stability in the southern Great Lakes and improve the understanding of earth viscosity structure and neotectonics of the region.The research will expose undergraduate geology majors to numerical models, statistical methods, advanced GIS practices and fieldwork. Their continued active participation inGeological Society of America sectional meetings and as co-authors on publications will stimulate the research environment of a small undergraduate geology department and encourage undergraduates to continue their education as researchers in graduate school and beyond.