Cape Cod Geology [Archive] - Fly Fishing Forum

: Cape Cod Geology

12-11-2000, 12:58 PM
I wanted to take this opportunity to recommend a great book entitled, " A Geologist's View of Cape Cod", by Arthur N. Strahler. It is a paperback and costs $7.95 for the 110 pages it contains. It is published by Parnassus Imprints, Box 335, Orleans ,MA. 02653. I purchased my copy at one of the book stores in Chatham but suspect that it can be found in any of the other bookstores on the Cape. Without providing a detailed book report, the table of contents reveals the following subject matter, " How Cape Cod was formed"; " What the waves have done"; " What the Tides have done"; " Ponds and Bogs of Cape Cod"; What the wind has done", and finally ," The soils of Cape Cod".The final chapter discuses the future of the Cape in Geological terms. The Book includes approximatly 60 illustrations, photographs, charts, and topographical mapes which visually explain the narration. There is also a list of further reading if one wishes to get into great "academic" detail. In any event, I wanted to point out a few issues it clarifies and explains which make this interesting and facinating reading for the non-scientists amoung us.

1)The Cape did not exist before the last ice age(Wisconsin stage). The zone was the present day continental shelf which was a dry plain.As the ice sheets spread, the farthest point south where it finally stopped in our area was Martha's Vinyard and Nantucket. You can see this today from the finger ponds and rivers on the south shore of the Vinyard which were created by Glacial till and flow of the ice melt. The second line of ice retreat was approximatly at the location of the mid-cape highway. The two large Ice sheets were known as the South Channel lobe, which ran along the lower cape, and the Cape Cod lobe which ran to the islands and then to the mid-cape. These two lobes were part of the massive glacier called the Laurentide Ice Sheet which covered most of North America.

2)The Book goes on to explain the melting away of the ice sheets which deposited the land matter it carried (glacial pluck). As it melted it created rivers of water and mud. These rivers are still there today on the south shore of the cape. The melting also produced outwash which formed the land itself. The sea level rose to the point of the highest outwash levels. Today , at nauset beach and elsewhere along the national seashore you can see Bolders(e.g. To the left of the beach from the parking lot), which fell off of the cliff scarps and probably originate from somewhere in Maine.

3) Two Interesting explainations are discused. Today you can still see scrapings on large bolders. These scrapings, called "glacial striations", show how the rocks came in contact with other bolders and bed rock(At parts to the north of the cape itself, since the cape has no bedrock), as they traveled in the glacial pluck. Enos Rock in Eastham and the bolders at the Naust coast guard station are examples plainly seen today. The second interesting point is the formation of the Kettle ponds(which are generally common knowledge, but just the same...). As the ice melted over the millenia huge chuncks of ice broke off the glacier and as water, till and outwash flowed from the main glasier, it would hit the chunks and deposit the material at and around the ice block. The flow would depost this material up to ,and at times, over the ice block . As the ice block melted the pond would form and the sides would collapse over the centuries. In fact , at the bottom of these ponds,you could dig a couple of feet down and reach the ancient surface ( Ground Zero). The book then goes on to describe the knob and Kettle landscape and the plains of Eastham, Truro and Wellfleet.

4) As the sea rose the ancient shore line of the cape was irregular and evidence of this shore line can be seen today as the western shore of Pleasant Bay,, Oyster pond, Orleans(at town Cove), Wellfleet harbor, and much of the Hyannis shore line.. As the waves and wind sculptured the eastern shoreline of the cape,and the sea flooded approximatly 2 to 3 to 4 miles of land to the east of Nauset, Wellfleet and Truro beaches and "hanging Valleys" appeared. Hanging valleys are evidence that the land had reached out substantial to the east. These valleys are where the present "hollows" are as well as other areas. They are valleys ,such as the Pamets rivers, which can be seen to end abruptly at the back of the huge dune cliffs that front the beaches. They were formed from Glacial outwash of the South channel ice lobe which flowed toward the bay side. The Chapter then goes on to describe incoming wave action, parts of a beach, marine scarps,storm wave errosion and wave refraction.

5) Another interesting discussion centers around beach drifting and the longshore current. For example, at Wellfleet on the ocean side the current splits into two directions, one south and one north. The north current formed the Provincelands and Race Point. The southern current formed Nauset beach and Monomoy Island. There is a description of Sand Bars and Sand spits. Monomoy is continuing it's march southward, infact, during the period between 1856 and 1868, as a result of violent weather patterns during that period,Monomoy Point was extended southward at a rate of 157 feet per year. There is discussion of Tombolos,And the growth of the Provincelands. An interesting point to note is that the ancient shoreline to the north actually ended approximatly a couple hundred feet south of Pilgrim lake at a place called "High Head". From that point north, including P-Town itself, Race Point and the Provincelands formed from Beach drift flowing northward. You can see all of this by going to High Head today and get a feel for what has transpired over the millenia, and look down from that hill and know that you are standing on the original "beach".

6) Finally there is descriptions of Tide activity and what that has contributed to mud flats and salt marshes, A description of ground water, when fresh water meets salt water, The cranberry bogs, Wind and Parabolic dunes, leaping sand grains, ventifacts and general soil composition.

Obviously, massive changes will not occur during our life times or that of our children or our children's children. Only the occational change similar to what happened to the beach infront of the Chatham Light or that description of Monomoy growth ,or the break between north and south Monomoy. Ah, but if I've got you hooked now and you want to know what the author says about the "geological" future. He says that what will happen is........

12-11-2000, 03:38 PM
FASCINATING! For those of us who have visited Cape Cod or are even luckier and have a long-term relationship with the Cape, your post reveals so much about the extraordinary place it is.

Thanks, I look forward to buying the book and deepening my own understanding of the cape's magic.

12-11-2000, 04:20 PM

Great Report! Another great reference (that's free) is to attend some of the Lectures offered at The Nation Seashore Welcome Center, Right off Rt-6 in Eastham. They do a lot on geology, as well as, nature walks to discuss the Flora & Fauna of The Cape. Also, a side trip to Doanne (sp?) Rock between the Welcome Center & Coast Gaurd Beach is well worth it. It is a Massive example of one of these Glacial Boulders.