The question of whether New Jersey is sinking is a complex issue rooted in both geological history and environmental changes. The state’s vulnerability involves two simultaneous processes: the global ocean surface is rising, and the landmass is slowly subsiding. This dual action accelerates the rate at which the coastline effectively moves inland, creating heightened coastal vulnerability.
Defining the Sinking Phenomenon
The concept of land “sinking” is scientifically termed subsidence, which is the gradual settling or sudden collapse of the ground surface. This process is fundamentally a lowering of the land’s elevation. In New Jersey, subsidence is generally slow and steady, measured in millimeters per year.
Subsidence must be distinguished from absolute sea level rise, which is the increase in ocean water volume due to thermal expansion and melting ice sheets. While the global ocean is rising, New Jersey’s land is simultaneously dropping, intensifying the impact. This local lowering adds directly to the effect of rising tides.
The combination of these factors means New Jersey experiences a higher rate of water encroachment compared to many other coastal areas globally. The effect is particularly noticeable along the low-lying coastal plain, where even small changes in elevation can translate into significant inundation.
Natural Geological Drivers
The primary geological reason for New Jersey’s subsidence is an ongoing process called Glacial Isostatic Adjustment (GIA). During the last Ice Age, massive ice sheets covered much of North America, pushing down on the Earth’s crust. This compression caused the crust around the edges of the ice sheet to bulge upward, forming a forebulge.
New Jersey was situated on this forebulge. Since the ice sheets melted thousands of years ago, the land that was once uplifted is now slowly collapsing back down. This “forebulge collapse” is a continuous, large-scale process that contributes an estimated 1.2 millimeters per year of sinking to the Mid-Atlantic region. The Earth’s mantle is still flowing to restore equilibrium after the immense weight of the ice was removed.
Additionally, the coastal plain of New Jersey consists of thick layers of unconsolidated sediments—sands, silts, and clays. These sediments are naturally prone to compaction under their own weight over millennia, contributing to the slow, long-term lowering of the land surface. This natural compaction is a constant factor in the overall subsidence rate.
How Human Activity Accelerates Subsidence
While geological drivers are unavoidable, human activities are accelerating localized land subsidence, particularly in coastal counties. The most significant factor is the withdrawal of groundwater from deep underground aquifers. These aquifers are composed of porous rock and sediment that are saturated with water, which provides structural support for the overlying land.
When large volumes of water are pumped out faster than they can be naturally replenished, the pressure within the aquifer drops significantly. This pressure reduction causes the fine-grained clay and silt layers to compress and compact permanently. This irreversible compaction translates directly into a lowering of the ground surface.
In southern New Jersey, groundwater withdrawal has caused estimated subsidence of 2 to 3 centimeters over the past two decades in the vicinity of some monitoring wells. This localized sinking compounds the effects of natural subsidence and rising sea levels, posing a serious threat to infrastructure and coastal economies.
Measuring Relative Sea Level Rise
The practical measurement of sinking land and rising water is captured by Relative Sea Level Rise (RSLR). RSLR is the localized change in sea level with respect to the land, representing the sum of global sea level rise and local land subsidence. This figure directly impacts coastal communities, accounting for the total apparent increase in water elevation.
Tide gauges, such as the long-running station in Atlantic City, provide the most direct measurement of RSLR. Data shows that sea level rose by about 1.5 feet between 1912 and 2021, which is approximately three times faster than the global average rate. The rate recorded in Atlantic City has been approximately 1.7 inches per decade.
This high rate of RSLR means New Jersey experiences increased tidal flooding frequency and accelerated coastal erosion. For instance, a projected rise of just 1.5 feet by 2050 would cause the 1-in-10-year flood event to exceed the highest flood level experienced over the last century in Atlantic City. The observed RSLR significantly magnifies the threat to the state’s low-lying coastline.