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

自17000年前的冰河晚期以来，五大湖地区的水文特性发生了重大而戏剧性的变化。大型冰川湖泊突然排干，地球缓慢的粘性变形导致出口垂直移动，影响了相关的湖泊水位。这项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其大地水准面的变形，这种变形是由于上一次冰河时代冰负荷的变化造成的。古冰川和冰后湖泊的海岸线现在相对于现在的大地水准面倾斜，提供了与时间相关的地球变形数据。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过去17,000年来整个五大湖地区不断变化的水文性质。由于数字高程模型(DEM)覆盖了整个地区，因此对该地区各地形变的预测可以计算出古地形。在给定现有地形(DEM‘s)的情况下，利用地理信息系统(GIS)来确定现代河流网络是很常见的。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水系和湖泊水位，随着消退的冰逐渐暴露在较低的出水口，以及由于均衡抬升导致的出水口高程变化，这些综合水系和湖泊水位不断变化。在地理信息系统中，可以很容易地计算出湖泊作为冰川破裂事件释放的淡水的准确体积。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快的气候变化。地理信息系统还可以通过量化向任何河流上的任何点提供地表水的总面积来确定古流域和河流网络。海岸线的预测将叠加在美国地质勘探局的数字栅格图形地形图上，用于实地检查预测，所有人都可以通过网站或光盘获得这些预测。这些预测也可以下载到连接全球定位系统(GPS)设备的手持计算机上，用于在现场精确定位海岸线特征的准确位置，无论是预测的还是观测的。逆模型将根据数据调整冰盖历史和地球流变学。成功的反演将产生预测的冰盖厚度历史，这对冰川学家和冰川地质学家试图了解劳伦蒂冰盖南端的动态性质很有帮助。这项研究还将有助于解决五大湖南部的地壳稳定性问题，并增进对该地区地球粘性结构和新构造的了解。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、高级地理信息系统实践和野外工作。他们继续积极参与美国地质学会分会，并作为出版物的共同作者，将刺激一个小型本科生地质系的研究环境，并鼓励本科生继续在研究生院及以后继续他们的研究人员教育。

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.