Direct Effects on Coasts by Glaciation

The New England states of northeastern United States are a good example of where glacial ice has had a direct and obvious impact on the coastal morphology – specifically along the coast of the state of Massachusetts and around the city of Boston. Between approximately 100,000 and 18,000 years ago, a large percentage of the North American continent was covered in a several kilometer thick sheet of ice that progressively advanced southward during this time. As this massive ice sheet advanced, it scoured and scraped the underlying ground. The scoured sediment was transported as the ice sheet advanced into progressively lower latitudes. Sediment was also carried by melt water streams that existed out in front of the ice sheet. The result is that glaciers and ice sheets such as this can move substantial amounts of sediment and act to create a unique suite of glacial landforms such as terminal moraines and outwash deposits. In fact, it is these types of deposits that formed the surface sediments of famous New England places such as Cape Cod, Martha's Vineyard, and Nantucket (Figure 2.6).

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Figure 2.6: Satellite image of Cape Cod, Massachusetts, which was created by the deposition of glacial sediment as the Laurentide ice sheet advanced. These glacially derived deposits of sediments have been reworked by coastal processes to create the unique shape of Cape Cod.
Image sourcet: NASA

Another type of direct effect that ice sheets and glaciers can have along the coast does not involve the deposition of sediment but rather the erosion of sediment and creation of features such as valleys. On a global basis, the modern day fjords were created during the most recent global-wide glacial event that lead to the advance and growth of ice sheets and mountain glaciers everywhere. It was during this period of time that the ice carved out what would later become known as fjords. Since 18,000 years ago, ice sheets and glaciers have been melting worldwide, and this extra water in the ocean basins has led to a rise in sea-level and flooding of the glacially carved valleys. In fact, famous fjords of places such as Alaska, Chile, and Norway are the direct result of glaciers once extending to the sea from high areas, carving very long and often deep but generally narrow valleys (Figures. 2.7, 2.8).

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Figure 2.7: Map of the Kenai Fjords National Park in Alaska. Notice the elongate valleys that extend form the mainland into the Gulf of Alaska. At the head of each valley is a glacier that would have, during the last Ice Age, extended down through the valley and to the then lower sea level.
Credit: National Park Service: Kenai Fjords National Park Alaska

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Figure 2.8: Aerial view of College Fjord in Prince William Sound of Alaska. During lowered sea level and cooler climate, the glacier at the head of the fjord would have extended through the valley and acted to carve out the valley by eroding sediment from the sides and base of the valley.
Credit: College Fjord, Prince William Sound 2007-08-07 by Erik Kohler