Image: JimIrwin (CC BY SA 2.5), via Wikimedia Commons
-- Impact of Ice Ages
The geology of northern New Jersey was heavily influenced by three separate cyclical periods of glacier flows during the Ice Ages, with the last intrusion occurring some 21,000 years ago when glaciers expanded from the north and then retreated as the climate warmed. The glacial flows pushed boulders, rock and soil in their path, carved valleys, eroded bedrock and flattened hills, and penetrated as far south as parts of current Hunterdon, Somerset and Middlesex counties. At their peak, the ice sheets at the Delaware Water Gap at the northwestern corner of the present state are estimated to have been 2,000 feet thick. The Kittatinny Mountains running parallel to the current northwest border of New Jersey were formed at one edge of the glacial intrusion; they now are the site in Sussex County of High Point, the highest point in the state at 1,803 feet above sea level.
Monument on top of High Point in Sussex County. Image: Famartin (Own work) [CC BY-SA 4.0], via Wikimedia Commons
The ice sheets gradually moved south, leaving ridges at their furthest point of advance called moraines; the Terminal Moraine forms a continuous ridge from Warren County along the Delaware River to Perth Amboy in Middlesex County and east to New York. As they melted, the glaciers left a mix of rock, silt and sediment captured in their movement.
The area between what is now the cliffs of the Palisades and the wetlands of the Meadowlands was formed, along with a deep freshwater lake known as Glacial Lake Hackensack. The lake later breached at the glacier's terminus in Perth Amboy and drained, exposing the lake waters after hundreds of years to Atlantic tidal flows as the ocean intruded miles inland as a result of rising water from the melting glaciers and leaving the Hackensack River and surrounding marshland. Much of the marshland was eventually filled in as it was diked or dammed by European settlers, but the remnants of the surviving wetlands are still apparent in the Hackensack Meadowlands.
-- Atlantic Coastal Plain
Most of southern and central New Jersey lies in the Atlantic Outer Coastal Plain, a geological formation created when the Atlantic Ocean, with its sea levels also influenced by the cyclical Ice Ages, repeatedly covered the coastal plain and then withdrew, depositing layers of sandy soil and leaving generally flat terrain. In New Jersey, the plain is subdivided into three sub provinces: the Inner Lowland (encompassing the low, broad valley along the Delaware River estuary), the Outer Lowland (along the southern New Jersey shore), and the Central Upland (encompassing an area of relatively low relief).
Twenty thousand years ago, the point where land met the ocean was at the edge of the continental shelf, some 80 to 90 miles to the east of the current New Jersey coastline. The ocean's intrusion inland continued into more recent times; property records from the 17th century in coastal counties identify lands now vanished under the Atlantic. Underground freshwater was left lying under the soil; the Kirkwood-Cohansey Acquifer, which is beneath the surface of the Pinelands and its outskirts, covers approximately 3,000 square miles, about a third of the state's total land area, and is estimated to include 17 trillion gallons of pure freshwater. The high water table and sandy composition of the area supported the growth of cedar, pine and some oak tree species which thrive in sandy, acidic soil. . Salt marsh grass also was prevalent until the land was filled in or farmed after the arrival of European settlers.
The last great high-stand in sea level began about 15 million years ago and left extensive marine sand and gravel deposits that cover much of southern New Jersey in the Kirkwood-Cohansey Acquifer. These highly porous sands are the subsoil of the vast region extending from the Pinelands to the sandy hilltops in the Atlantic Highlands region. In the Pinelands, the marine and alluvial gravel deposits created hills with elevations between 120-200 feet. In the Atlantic Highlands region, these deposits are on hills ranging between 200-373 feet in height. Unlike the bedrock found along the New England coast, none of the sediments, which are the source of New Jersey's beaches, exposed at the surface in Monmouth, Ocean, Atlantic or Cape May Counties are cemented and thus erode easily from the effects of tidal waves and storms.. Seventy miles off the Jersey Shore, however, sediment accumulation on the Atlantic continental margin has left a great wedge of material, consisting of a stacked sequence of sedimentary rock formations that are estimated at some 30,000 feet in thickness near the break in the continental slope.
The rise in global sea level has been occurring for the past 20,000 years at a variable rate, following the melting of the last great ice sheet covering northern North America. The local change has been in the range of 350 feet to 400 feet vertically, which has produced a long-term westward migration of the shoreline. The consensus of most scientists is that global warming will result in a more rapid rise in sea levels,