Geology
Long Island, as part of the Outer Lands region, is formed largely of two spines of glacial moraine, with a large, sandy outwash plain beyond. These moraines consist of gravel and loose rock left behind during the two most recent pulses of Wisconsin glaciation some 21,000 years ago (19,000 BC). The northern moraine, which directly abuts the North Shore of Long Island at points, is known as the Harbor Hill moraine. The more southerly moraine, known as the Ronkonkoma moraine, forms the "backbone" of Long Island; it runs primarily through the very center of Long Island, roughly coinciding with the length of the Long Island Expressway.
The land to the south of this moraine to the South Shore is the outwash plain of the last glacier. Part of this, known as the Hempstead Plains, supported one of the few natural prairies to exist east of the Appalachian Mountains.
The glaciers melted and receded to the north, resulting in the difference between the North Shore beaches and the South Shore beaches. The North Shore beaches are rocky from the remaining glacial debris, while the South Shore's are crisp, clear, outwash sand. Running along the center of the island like a spine is the moraine left by the glaciers. (Bald Hill is the highest point along the moraine.) The glaciers also formed Lake Ronkonkoma, a kettle lake.
The island's tallest natural point is Jayne's Hill near Melville, with an elevation of 400.9 feet (122.2 m) above sea level. Long Island is separated from the mainland by the East River, which is actually not a river, but a tidal strait. Long Island Sound forms the northern boundary of the island.
Long Island contains a series of sand and gravel aquifers, geologic formations which can hold, transmit, and yield water in usable quantities. All of Long Island's water supply comes from underground water reserves held in aquifers. Stacked one on top of the other like layers in a cake, three major and one minor aquifer make up the Long Island aquifer system. In sequence from shallowest to the deepest, the Long Island aquifers are: the Upper Glacial, the Magothy and the Lloyd Aquifers. All Long Island aquifers receive their fresh water from precipitation which takes from 25 to 1,000 years to migrate through the layers to the aquifers, which hold roughly 70 trillion US gallons (260 km3)—enough to flood the entire surface of Long Island with more than 300 feet (90 m) of water—and can withstand long droughts that could dry up surface-water reservoirs like the ones that supply New York City. Almost four million gallons each day are taken from beneath Nassau and Suffolk Counties, providing the primary source of water for the resident population. While most homes are on a municipal water system, there are still many areas where homes have their own wells to provide water. Both Nassau and Suffolk counties have long recognized their dependence on the aquifers and have stipulated that recharge basins (known locally as sumps) be built to collect ground water. Recharge basins are required and sized based upon the scale of any new development on Long Island. Due to contamination associated with development, concern to preserve the quality of Long Island's groundwater has become the single most important factor limiting the region's growth.
In a 1985 decision, the U.S. Supreme Court treated the island as a peninsula for the purposes of a boundary decision.
Read more about this topic: Geography Of Long Island