Brrr.... Harding's Beach and Glaciers
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Standing on the location, the geocacher is standing on ground once covered by glaciers! The coastline and the various coves and embayments to the west, north and east are all unique geological features.
The purpose of this earthcache is to highlight Chatham's glacial history and the unique geological and hydrological conditions which are still in transition today.
Note: The parking area for Harding's Beach requires a fee during the summer season roughly between 9 a.m. and 4 p.m. (give or take). It is free at other hours and during the non-summer months. It is free for walkers and bicyclists all the time.
Note 2: Wheelchair boardwalk located on west side of beach accessible from parking lot.
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In order to receive credit for this cache, you must do the following:
1. OPTIONAL: Post a picture of yourself with your GPS in hand at the listed coordinates; and/or
2. REQUIRED: Answer the following three questions and email them to me:
a. Where do you estimate that today's beach and dune deposits meet the outwash deposits from the glacial era.
b. Looking southeast, you can see Monomoy National Wildlife Refuge. Is this island an outwash deposit or a beach and dune deposit?
c. Is the sand on this beach naturally occurring or is it shipped in from elsewhere? (Extra bragging rights if you can tell us where it comes from IF it is NOT naturally occurring here.)
Once you have the answers, email them to me for credit. Any posted logs which do not have accompanying answers in a reasonable amount of time will be deleted without notification.
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The geologic history of Cape Cod mostly involves the advance and retreat of the last continental ice sheet (named the Laurentide after the Laurentian region of Canada where it first formed) and the rise in sea level that followed the retreat of the ice sheet. On Cape Cod, these events occurred within the last 25,000 years, and many can be dated by using radiocarbon techniques.
Sometime after 23,000 years ago, the glacier reached its maximum advance, a position marked approximately by the islands of Nantucket and Martha's Vineyard (just over the horizon to the south of your current location). The ice sheet was characterized by lobes that occupied large basins in the bedrock surface. These lobes were responsible for the location and overall shape of Cape Cod and the islands. Thus, the western side of Cape Cod was formed by the Buzzards Bay lobe, the middle part by the Cape Cod Bay lobe, and the lower or outer Cape by the South Channel lobe, which occupied a deep basin to the east of the Cape. During the maximum ice advance the landscape, where Cape Cod was soon to be, was glacial ice to the horizon.
Within a few thousand years or possibly less, the ice sheet started to retreat rapidly, and by 18,000 years ago, it had retreated away from Cape Cod and into the Gulf of Maine, which lies to the east and to the north of the Cape. Thus the retreat of the ice from the islands to a position north of Cape Cod may have taken only a few thousand years. By roughly 15,000 years ago, the ice had retreated from the Gulf of Maine and all of southern New England.
The rock debris deposited by glaciers is called drift. It overlies bedrock that is similar to the hard rock that crops out throughout the rest of New England. On Cape Cod, the bedrock is buried by glacial deposits ranging from more than 200 to more than 600 feet thick. Drift consists of very fine to very coarse rock debris. If unstratified and unsorted, it is called glacial till. Till is deposited directly by ice and is unsorted because ice cannot separate rock fragments of different sizes. Thus, it is a mixture of all sizes of rock debris ranging from clay-sized particles to very large boulders. Stratified drift, on the other hand, is deposited by water which can separate the different sizes of rock fragments. The rock fragments are deposited in layers called strata. Gravel and sand are sorted and stratified by meltwater flowing in streams draining the glacier. The clay and silt-sized particles are carried by the meltwater streams into quiet water (glacial lakes or the sea) where they settle out according to the size of the particles; the coarsest, first, and the finest, last. Meltwater stream sediments that are laid down over and around glacial ice are called ice-contact deposits and generally consist of sand and gravel, but locally include silt and clay, till, and large to very large boulders.
The distribution of the glacial deposits on Cape Cod is shown by the generalized geologic map on the listed website. Most of the drift has been fashioned into either moraines or outwash plains. Both features mark positions of the ice front. Moraines are ridges of drift formed by moving ice. Most moraines are formed when the ice front remains more or less in the same place because advance of the glacier is balanced by melting along the ice front.
When the debris falls free of the ice, it accumulates along the ice front much like material at the end of a conveyor belt. However, the Buzzards Bay and Sandwich moraines were formed in a different way. They were formed when an advancing ice front overrode sediments it had previously deposited or sediments that were older than the last glaciation. The advancing ice thrust sheets of drift upward and forward to form a large ridge beyond the ice front. Thus, the formation of the moraine more closely resembles the work of a bulldozer rather than a conveyor belt.
You are currently standing on beach and dune deposits of sand which tides have accumulated on the edge of the outwash deposits visible (though now covered with vegetation) directly to the north.
The indented coastline from Eastham southward to Chatham also owes its existence to the Laurentide ice sheet. Most likely, it represents the last remnant of an irregular coastline made up of headlands and embayments that marked the eastern limit of the glacial Cape. It also represents a western expansion of the South Channel lobe in the form of a sublobe, which at its largest size, occupied the site of the Eastham outwash plain as well as limiting the eastern extent of the Harwich outwash plain and the distribution of the Nauset Heights deposits.
At the end of glaciation and before the landscape was well covered with vegetation, winds blowing across the barren glacial deposits, including material from the exposed bottoms of drained glacial lakes, picked up sand, silt, and clay and deposited this material as a thin almost continuous blanket on the drift surface. Stones lying on the drift surface were cut, faceted, and polished by sand blasting. These stones, called ventifacts, have been moved into the windblown layer by frost action. They are distinctively shaped and some have been mistaken for tools of Indian origin.
The windblown material and the upper part of the underlying drift make up the parent material for Cape Cod soils. These soils are called podzols and are typical of young soils developed on a sandy parent material in a temperate climate under forest cover.
Additionally, from where you are standing, you are surrounded by a unique system of embayments and estuaries. Embayments consist of harbors connected to the Atlantic Ocean and Nantucket Sound and tidal estuaries. Estuaries are places where fresh and salt waters meet and mix and are some of the most productive ecosystems on earth.
Walking east from this position, you will eventually arrive at an old lighthouse and the mouth of the Stage Harbor system. Two tidal rivers lead off the harbor, Oyster River, which connects the harbor to Oyster Pond, and Mitchell River, which connects the harbor to Mill Pond and Little Mill Pond.
Walking west along the beach from this point, you will encounter the mouth of the Sulphur Springs System. The system consists of Cockle Cove Creek, Bucks Creek and Suphur Springs. Cockle Cove is a salt marsh with a
central tidal creek which drains almost completely at low tide. Sulfur Springs is a shallow embayment at the head of Bucks Creek that is transitioning to a salt marsh. The entire system is undergoing ecological change resulting from the constant physical change at the mouth of Bucks Creek.
Sources:
1. U.S. Geological Survey (USGS). Website belongs to the U.S. Department of the Interior, USGS and is maintained by Donna Newman. Last Updated: 6 November 2001.
2. Friends of Chatham Waterways. "Chatham's Waters."
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CONGRATS to golfgods and plumb69 for their First to Find (FTF) on 4 Feb 2012!
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Additional Hints
(Decrypt)
Cebonoyl qba'g arrq bar sbe guvf.