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Unformatted text preview: Earth Sciences 1081b 2011 Lab #3: Campus Geology and Flooding Lab 3: Geology of the UWO Campus and Flooding of the Thames (Background Pages for Lab) OVERVIEW Flooding is a natural part of stream systems and while it is tempting to immediately associate floods with the negative effects on humans, there are some important aspects of flooding that can, in fact, be beneficial to people on the long term (e.g. renewing nutrients to soils developed on floodplain areas). That said, the negative impacts of flooding and other stream processes on humans may be substantially reduced with some basic knowledge of how streams work and the time scales at which events such as floods operate. In this lab, we will examine some of the features associated with our nearest streams, namely the Thames River and Medway Creek, the flood history in our area, and some of the measures that have been taken reduce the incidence of severe floods. The Significance of Recent Geological History on Flooding Tendency in London, Ontario The City of London, Ontario, has always been rather prone to flooding, and this is partly due to the natural topography of the land on which it is established. This natural topography in turn, is a function of our area’s recent geologic history. Ever wonder why there is no bedrock exposed in the immediate vicinity of London (despite the significant exposures of carbonate rocks in the nearby towns of St. Mary’s and Ingersoll)? The main reason is that much of London occupies an elongate, low-lying depression that a mere 10,000 years ago was a huge lake (which geologists refer to as Lake London)! The development of the lake was itself was a consequence of the melting of the massive ice sheets that once covered all of southwestern Ontario during the last ice age. Keep in mind that all the meltwater produced during deglaciation had to go somewhere and the natural depression in the London area, bounded on all sides by moraines (ridges of glacial sediment produced at the edges of glacial ice lobes) was an obvious place for it to pool (Figure 1). The huge torrents of glacial meltwater that drained into Lake London carved the wide valleys that are now occupied by the much smaller present-day channels of the North and South valleys of the Thames River (at the time the original valleys were formed, the water level of the Thames River would have been only slightly lower than the floor of your lab room (B&GS Rm. 1015)! As the land rebounded (a response to the weight of 2 km of glacial ice having being removed), Lake London eventually drained. However, compared to the land area surrounding, much of London is still low-lying, and as a consequence, As a consequence, the bedrock beneath London is completely concealed by the sediments that accumulated here during, and shortly after, the last Ice Age. That London occupies a low-lying area also accounts for the fact that spring flooding is common in some parts of London (with cars in the parking lot of Elgin Hall being obvious casualties of such events),...
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- Fall '11