![]() These boulders are most abundant on the terminal Many large boulders, or "glacial erratics", are found on Long Island as part of the moraine deposits. In addition to the major glacial features (terminal moraines and outwash plains) there are several smaller glacial land features found on Long Island. Hill terminal moraine and the stream drainage had adjusted to the post-glacial contours of the land. Shoreline erosion was occurring along the Harbor To the oceans, to drown hundreds of square miles of outwash plain and to fill Long Island Sound. Sea level rose with the return of meltwater The picture above depicts a section of eastern Long Island after the continental glaciers retreated to the north. Read About the Glacial History of Long Island here Moraine became more discontinuous than the Harbor Hill moraine. Moraine had already been formed and was being cut through by streams coming from the melting ice to the north. The streams carried sands and silt across the flat coastal plain to form broad glacial outwash plains. Meltwater streams flowed south to the distant Atlantic Ocean which was over 350 feet below its present level because of the vast amount of water The picture above shows a section of eastern Long Island as it may have appeared when the glacier was melting along the Harbor Hill moraine. The highest points on Long Island are found along the terminal moraines. Thus only the Harbor Hill moraine remains to mark the position of the stationary iceįront west of Lake Success. Overriding and destroying the Ronkonkoma terminal moraine. West of the juncture the Harbor Hill ice moved south, Ice retreated from the Ronkonkoma to the Harbor Hill position and the two moraines are seen. If you look at the map at the top of the page you can notice where the moraines intersect near Lake Success. The accumulation of rock debris along these two stationary melting fronts formed two prominent ridges called The Ronkonkoma and the later Harbor Hill are two sub-stages, or positions, of this ice sheet The geologic event that most greatly affected the land surface of Long Island was the advance of a massive continental glacier into this regionÄuring the Wisconsin stage of the Pleistocene Epoch. Therefore, is an important, but little visible, contributor to Long Island's topography. However, because of the glacial cover, exposed Cretaceous sediments are limited to a few scattered localities on present day Long Island. The figure below shows the areas above sea level as they might appear if they had not been covered by the younger glacial deposits. The top surface of the Cretaceous reaches elevations above sea level over an extensive area of northern Nassau and northwestern ![]() Is over 2,000 feet thick under Fire Island, but it thins towards the north shore and the western end of the Island to pinch out under Long Island's Sound, Resting on the bedrock and extending under nearly all of Long Island is a massive wedge of Cretaceous sediments (sands, clays and gravels). The bedrock slopes down to the south and east beneath the rest of Long Island and therefore does not form any significant landforms here. Surface exposures of the bedrock are widespread in Manhattan and the Bronx but are limited on Long Island to small outcrops in northwestern Queens. The foundation upon which Long Island rests, and the deposition of sands and clays on this bedrock 70 million years ago, during the late Cretaceous period. Pre-glacial geologic events in the Long Island include the formation of the ancient (over 400 million year old) metamorphic bedrock that forms ![]() Whether they occurred before, during or after the advance of a continental glacier onto the Island. On Long Island these processes can be grouped into three categories - pre-glacial, Each natural land feature originated through the action of some The surface of Long Island is made up of many varied and interesting landforms. ![]()
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