The Provincelands Hook, an area of marshes and dunes, was built out from the northern end of the glacial deposits of Outer Cape Cod. The hook, a wedge 60 m at its thickest, of marine, beach, and dune material, rests in part on Tertiary Coastal Plain sediments that are probably only an isolated patch on the crystalline basement. About 18,000 years ago, when late Tazewell ice melted away from the region of present day Cape Cod, the Gulf of Maine was filled with ice, and Georges Bank was above sea level. Between 18,000 and 6,000 years ago, sand that eroded from the coast was moved along the east side of Cape Cod from north to south, where it accumulated as a part of the sand wave complex southeast of the cape. Waves from the east and southeast that would have tended to move sand northward along the Capo were blocked by Georges Shoals and Nantucket Shoals. By 6,000 years ago, sea level had so risen that deeper water over Georges Bank permitted more waves to reach Cape Cod from the east and southeast. The dominant direction of littoral drift which had been to the south, then received a strong north component and material moved northward, accumulating to form the Provincelands Hook. Based on 14C dates and other evidence, the hook formed between 6,000 years ago and the present and is still growing. Shoreline reconstructions are guided by 14C dates, well information, regional topography, and known behavior of hooks. It is noted that hooks are characteristic features of Cape Cod spits and tend to trap lakes behind them. The depressions containing lakes in the modern Provincelands are interpreted as low areas trapped behind hooks. A change in the growth habits of spits is thought to have taken place about 2,000 years ago, coinciding with the abrupt decrease in the rate of rise of sea level.
When a grain of sand is delivered to the sea by erosion it begins a journey being transported along beaches or bars, or offshore by waves and currents. The history of this journey can be extremely complex for the grain might spend a few seconds in one place and many years trapped in another before being released again for travel. It is therefore important at the outset to place some limitations upon our study. Firstly, our time scale is limited to the past seventy years, the time over which data were gathered. Secondly, the geographical position is limited to a strip of the east coast of Cape Cod 29,400 yards in length (Figure 1), extending seaward to where water depth is about forty feet. After a grain of sediment leaves this area we are no longer concerned with it. We define residence time as the average number of years a grain of eroded sediment is likely to spend in this prescribed area before it is transported elsewhere. We will further try to show that sediment takes a preferred path, some of it moving along the beach and some along the bars. It makes no difference to us if specific environments share grains; that is to say, some material will be on the beach one day and on the bar the next. In the end those grains which tend to be more stable in the beach environment will spend more time there and will travel with a characteristic velocity which is different from the velocity of those grains which are in hydrodynamic equilibrium on bars. The method used to compute residence time involves volume stability. We measured the volume of the beaches and bars in the definition area and assumed that these volumes have not changed within the time limits of our study. We also measured the yearly addition of sediment to the area. In-as-much as there is neither gain nor loss of the average volume of sand -built features, i.e., the beaches and bars, sand must be moving out of the study area at the same rate it is being introduced. Therefore, the residence time in years is the average volume of a beach or bar divided by the yearly volume of sediment added by erosion to the beach or bar.
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