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How did the Harbor Hill and Ronkonkama Moraines help shape Long Island?
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glacial landform
Eskers,
or narrow
ridges of
gravel and sand left by a retreating glacier,
wind through western
Nunavut, Canada, near the Thelon River.
The Harbor Hill and Ronkonkoma Moraines are fundamental to the geography of Long Island, as they serve as the primary terminal moraines that frame the entire island.1
These landforms were created by the Laurentide Ice Sheet between 22,000 and 18,000 years ago, when the glacier deposited vast amounts of till and outwash sand at its margins. Beyond their role in defining the island's structure, these glacial sediments were later reshaped by stream and coastal processes, eventually forming the sandy barrier islands located off the south shore of Long Island.1