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What is a terminal moraine

what is a terminal moraine

Geocache Description:

Park safely on Satterlee Street at the southern-most end of Hylan Boulevard and proceed along the paved path towards the beach, past the historic stone-walled Conference House.

Once you reach this waypoint you are standing at the very last advance of a Pleistocene Epoch glacier that occupied a major portion of North America approximately 15 thousand years ago. At this point in geologic time, the climate was much colder as a massive continental glacier, known as the Laurentide Ice Sheet, advanced downwards from Canada into and across New York State. Imagine now the nearest beach is located close to the edge of the present day continental shelf, beyond the visible horizon.

Moving like a giant bulldozer, this ice mass picked anything and everything in its path from house-sized boulders to silt and clay particles. This last particular glacier (there were possibly 5 advances) approached Staten Island from the north-northwest and flowed to the south-southeast. As such it has been assigned on the geologic time scale to be of Late Wisconsin age of the Quaternary Period. The resulting line of heterogeneous debris formed a sinuous mound, marking its final progress. This mound is called a terminal moraine or more specifically the Harbor Hill Terminal Moraine. This moraine continues southwestward into New Jersey and Pennsylvania approximately adjacent to Interstate Route 80; to the northeast it continues along the eastern margin of Staten Island across the Narrows to Brooklyn and makes up the hilly regions along the north shore of Long Island, and finally up into Connecticut and to Rhode Island. Another older moraine known as the Ronkonkoma can be found along Long Island’s south shore, but it does not exist in Staten Island.

As the climate became slowly warmer, the glacier began to retreat or melt faster than its forward motion. As this happened, meltwater streams returned water to the ocean, raising sea level approximately 300 feet to more or less its present location. The last of this continental glacier probably melted about 12,500 years ago. Examining the components within this mostly unsorted and unstratified red-brown mass will determine the path that the glacier took to arrive at its present locality. You will find many rock and mineral specimens in place within the mound and many that have weathered out of the moraine and tumbled onto the beach face below. All three rocks types may be found here: sedimentary, igneous, and metamorphic. These include sedimentary rocks from the nearby Triassic-aged Newark Basin of the Mesozoic Era, which consists of pieces of black shale from the Lockatong Formation, red-brown feldspar-rich sandstone from the Stockton Formation and fine-grained red shale from the Passaic Formation. Also, from the Mesozoic Era and early Jurassic Period are dense chunks of grey to rusty weathering Palisades Diabase, which is a coarse-grained and dark-colored igneous intrusive rock that makes up the “Palisades” cliff

along the west side of the Hudson River. In addition, you will find many mineral pebbles of black smoky quartz and iron-stained yellow milky quartz. Metamorphic rocks found are grey quartzite cobbles, rotten pebbles of mica-rich schist, and large boulders of white-yellow- and grey-banded gneiss. The existence of these rocks means they must have been exposed at the surface to the ice’s path in order to be incorporated within the moraine. However, this last glacial advance may have picked up and re-worked moraine deposits from earlier glacial events here. All of this glacial material overlies the 85 to 93 million year old Cretaceous-aged sediments of sand and clay which are not visible at this locality, marking a large time gap known as an unconformity or more specifically as a disconformity where 80 million years of geology is missing via erosion or because sediments were never deposited. The hidden underlying Cretaceous-age formations can be found further northeast along the beach at another earthcache locality. This was the last of perhaps five glaciations that the New York area had suffered in the last 2 million years. Above portions of this moraine are finely stratified layers of silt and sand known as glacial outwash, that were deposited by streams of glacial melt water on its way back to the ocean. Also noticeable at the very top of the outwash are discrete piles of discarded oyster shells otherwise known as garbage pits or middens as archaeologists call them. Oysters were extensively used for food by the Lenape Indians that later occupied this area within the Raritan Bay region.

As a quick historical note, the nearby stone Conference House is mostly composed of glacially deposited boulders and cobbles from the moraine. If you examine the rocky components that form the major walls of the dwelling, you will see a good representation of the rocks found within this moraine that served as a locally abundant source of building materials. Also examine the cement that holds these rocks together, especially the small white chalky bits. The abundant oyster shells from the nearby middens were ground up and added as part of the sandy cement. The structure is the Billopp Manor House as it is formally known, was built in 1680. It was the site of the historic Staten Island Peace Conference. Admiral Lord Howe, Commander of His Majesty's Atlantic Squadron, invited Ben Franklin, John Adams, and Edward Rutledge to a 3-hour meeting that took place on September 11, 1776. Howe’s intention was to persuade the Colonists to return to the folds of the British Empire. His offer included freedom from reprisal and the addition of more of the rights enjoyed by other Englishmen. Well, its obvious today this meeting didn’t go very well! Tours of the interior are available.

To get credit for this Earthcache, estimate the thickness of the moraine at the stated coordinates.

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