Box 12 Cenozoic Glacial Sediments An Engineering Legacy

During the Cenozoic Ice Age approximately 30% of the Earth's land surface was glaciated and as a consequence over 10% of our land is now covered by glacial sediments - tills, silts, sands and gravels. In a country such as Britain this proportion is even higher. Any form of construction on or in these sediments must consider their engineering properties. At what angle will the sediment stand if excavated? How will they respond when loaded? How variable are they? How permeable are they? These questions can be answered only by a detailed knowledge of the sediments and of the processes that deposited them: the contribution of the glacial geologist.

A good example is provided by a proposed development at Hardwick Air Field in Norfolk. In 1991 Norfolk County Council applied for planning permission to build a waste hill (land raise) 10 m high to dispose of 1.5 million m3 of domestic waste over 20 years. Crucial to their proposal was the assertion that the area was underlain by glacial till, rich in clay, which would act as a natural impermeable barrier to the poisonous fluids (leachate) generated within the decomposing waste. Normally an expensive containment

liner is required to prevent contamination of the ground water by the leachate. This proposal became the subject of local debate and as a consequence the planning application was called to public planning enquiry in 1993. At this enquiry the objectors used a detailed knowledge of glacial till to argue that it was inadequate as an impermeable barrier in its natural state. Till contains fissures and pockets of sand through which the leachate may pass. The proposal was rejected, partly on the basis of this evidence. This example illustrates how knowledge of glacial sediments is vital to making engineering decisions within glaciated terrains.

Source: Gray, J.M. (1993) Quaternary geology and waste disposal in South Norfolk, England. Quaternary Science Reviews, 12, 899-912. [Modified from: Gray, J.M. (1993) Quaternary Science Reviews, 12, figure 9, p. 905].

Patagonia. These ice sheets dramatically changed the landscape beneath them and have left a record of their presence in the form of glacial landforms and sediments. This record shows that these ice sheets are not only a consequence of oscillations in global climate, which has driven their growth and decay with amazing regularity during the past two million years, but that they have also helped to drive climate change by modifying and interacting with the atmosphere. Understanding these ice sheets and glaciers is vital if we are to understand the mechanisms of global climate change.

In many parts of the world a distinct landscape composed of many different landforms and sediments was created by the glaciers of the Cenozoic Ice Age. This glacial landscape still survives today. It determines the distribution of valuable resources such as aggregates, and the way in which we build roads, railways, factories and houses (Box 1.2). The aesthetic appeal of this glacial landscape, to be found in many upland areas of North America and Europe, for example, is also the product of these glaciers. The spectacular mountain scenery is the result of glacial erosion, whereas glacial deposition often produces a gently rolling landscape. If we are to understand the form and texture of this glacial landscape we must understand the glaciers that produced it.

The landforms and sediments left by these glaciers are the clues from which they can be reconstructed and their behaviour studied. This subject, palaeoglaciology, is of increasing importance as we seek to understand how the glacial system interacts with other parts of the Earth's global system. By studying glacial landscapes and reconstructing the glaciers that created them we can examine the way in which glaciers grow, decay and interact with climate. From such research we can begin to predict what will happen when the mid-latitude ice sheets next return because, although the present is optimistically termed the Postglacial, there is no reason to suppose that large glaciers or ice sheets will not return to the mid-latitudes in the future.

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