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Coastal Erosion on Cape Cod: Some Questions and Answers
Robert N. Oldale
NOTE - This publications appeared in the 1999 CAPE NATURALIST, the journal of the Cape Cod Museum of Natural History, volume 25, pages 70-76.
Introduction / Questions & Answers / Conclusion / References
Billingsgate Island, 1910, before the entire island was eroded away. Photograph provided by the Cape Cod National Seashore.
All that remains of Billingsgate Island of Wellfleet is a shoal exposed during very low tides, 1991. The fate of Billingsgate Island may be a precursor for Cape Cod as the sea continues to erode the fragile land. Photograph by Dann S. Blackwood, U.S. Geological Survey.
The 1987 breach in North Beach in Chatham (Wood, 1991) and the subsequent loss of homes to the sea, the ongoing storm wave erosion along the great east facing sea cliff that runs from Eastham to Truro (Fig. 1),
and severe northeast storms, for example, the Halloween storm of 1991, the December storm of 1992, and the "storm of the century" of 1993, focus attention on the coastal erosion of Cape Cod. Many people view coastal erosion as a problem that needs to be addressed and, if possible, prevented. However, storm wave erosion along the shore of Cape Cod (Fig. 2)
|Figure 1. Map of Cape Cod showing location of major villages and towns. Click on figure for larger image (80KB).|
has been going on for thousands of years and will likely continue for thousands of years more. It is nature's way of supplying the sand necessary for Cape Cod to adjust to a rising sea level and to build and nourish beaches, barrier islands, barrier spits, and sand dunes. Without coastal erosion, the Cape we know and enjoy would not exist. There would be no sea cliffs, beaches, or barrier islands. There would be many fewer protected bays and harbors, as well as fewer salt marshes and sand flats, all of which are important habitats for marine life. However, erosion is a natural process that can result in the loss of private and public property and is thus a serious concern to many people who live or summer on the Cape. Coastal erosion also impacts other parts of southeastern Massachusetts. The questions posed here and answers apply equally well to the islands of Martha's Vineyard and Nantucket.
|Figure 2. Map of Cape Cod showing shores undergoing erosion (cliffed sections) and shores characterized by marine deposition (barriers). Click on figure for larger image (120KB).|
These questions about coastal erosion on Cape Cod were posed by Sarah Dinwoodey, when she was a ninth grade student at Wellesley High School. She has spent her summers in Chatham on Cape Cod and was very concerned about the breach in the barrier off Chatham (Fig. 3)
and the subsequent erosion along the mainland shore. I was impressed by the appropriateness and scope of Sarah's questions and believe that many other people, of all ages, might ask similar questions in an effort to understand coastal erosion and the part it plays in the formation of Cape Cod.
|Figure 3. Chatham breakthrough seen from the air during summer of 1991. Click figure for larger image (185KB).|
My answers to Sarah's questions may seem uncaring for the people of Cape Cod who are losing property to the sea. This is because, as a geologist, I view coastal change in the long term (on the order of a thousand years or tens of thousands of years) and because I recognize the inevitable loss of this fragile land to the sea. Some of my answers may seem ambiguous. This is because I am somewhat aware of what the scientific community knows and doesn't know about coastal processes, global warming, and sea-level rise. Here are some of Sarah's questions and my answers to these questions.
Title Page / Introduction / Questions & Answers / Conclusion / References
Cape Cod's "Magic" Quartz Pebbles
Geologic History of Cape Cod, Massachusetts
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