A Rutgers scientist explains how dark sand, clear water, sudden cold spells and other forces continually reshape the coast

The Jersey Shore may look familiar from summer to summer, but it is never truly fixed. It is an evolving coastal system in which sand color, beach width, water clarity and even ocean temperature can change quickly.

Few scientists know this shifting landscape as well as Rutgers geologist Kenneth Miller. A Board of Governors Professor in the Department of Earth and Planetary Sciences in the Rutgers School of Arts and Sciences, Miller is a stratigrapher, paleoceanographer and micropaleontologist whose research focuses on sea-level change, ocean history and the development of the New Jersey continental margin. He has led major coastal and offshore drilling projects and published more than 230 peer-reviewed studies during a career spanning more than four decades.

Rutgers geologist Kenneth Miller says the Jersey Shore is never truly unchanging. Waves, winds, tides and currents continually move sand and reshape the coastline.

Miller explains what beachgoers are seeing when one beach has darker sand than another, the water suddenly becomes clear or cold and storms transform a familiar stretch of coast.

Is the Jersey Shore ever truly still?

No. Beaches are constantly adjusting to waves, winds, tides and currents. Sand moves along the shoreline and between the visible beach and offshore areas, changing the beach's width, slope and shape.

Small changes can occur from one day or week to the next. The most dramatic reshaping generally happens during powerful storms, particularly winter nor'easters, when high-energy waves can remove large amounts of sand from the beach and deposit it offshore.

Some of that sand may return during calmer conditions. Some may be carried elsewhere along the coast.

What causes the sand to look different from one beach to another?

The size, color and composition of beach sand reflect where the sediment came from, how it traveled and how waves and currents sorted it.

Most New Jersey beach sand consists primarily of light-colored quartz. Some beaches also contain greater concentrations of darker, denser minerals. Wave action can separate these grains from lighter quartz and concentrate them in streaks or patches.

Beach nourishment, the process of adding sand to an eroded beach, has altered the sand found on many New Jersey beaches. The predominant grain size at many beaches today is strongly influenced by the offshore locations from which replenishment sand was pumped.

Measurements conducted in 1956 documented the natural grain sizes of New Jersey beaches before large-scale beach nourishment changed many of those original patterns.

What makes Long Beach Island geologically distinctive?

Long Beach Island is the northernmost true barrier island in New Jersey. North of LBI, the coastline begins to transition into barrier spits and beaches attached to the mainland rather than detached barrier islands.

LBI also lies near a dividing point in the movement of sand along the coast. Sand generally moves northward along beaches above LBI and southward along beaches below it.

Its sand is typically medium-grained, with particles about 0.25 to 0.5 millimeters across. It tends to be finer than sand found farther north and coarser than sand on some barrier islands farther south.

These differences reflect variations in the sources of the sediment and in wave energy along the coast.

What creates the dark streaks that sometimes appear in beach sand?

The streaks are usually concentrations of heavy minerals such as glauconite, zircon, tourmaline and rutile.

Because those minerals are denser than quartz, waves can sort and concentrate them into thin layers. The streaks may be especially noticeable after storms, when energetic waves move and rearrange large amounts of sand.

As the water slows, the heavier grains tend to settle first.

Why can the ocean look especially clear and blue?

Clear water often follows a period of calm weather. When waves are small and there have been no recent storms, sand and other suspended material can settle to the bottom.

Wind direction also matters. Certain winds can move surface water away from the coast and draw colder, clearer water upward from below through a process called upwelling.

That water may initially look strikingly clear. Over time, however, nutrients carried upward by the colder water can stimulate algal growth, giving the water a greener or occasionally reddish appearance.

Why does the water become cloudy again?

Wave activity and storms are the main controls of water clarity. Strong waves stir sand and sediment from the sea floor into the water, producing a cloudy or brownish appearance.

Winds also influence currents and mixing. Depending on their direction and strength, they can allow sediment to settle, stir additional material into the water or trigger upwelling.

Does clear-looking water mean the water is clean?

Water clarity and water quality measure different things.

Cloudiness is often caused by harmless suspended sand and sediment. Bacteria and other pollutants may be present even when the water looks perfectly clear, and they cannot be detected simply by looking at it.

Official water-quality testing provides a much more reliable measure of whether water is safe for swimming.

Why can the ocean suddenly feel cold during a heat wave?

The change is often caused by upwelling. Winds can push warm surface water away from the coast, allowing colder water from deeper offshore areas to rise and replace it.

That process can lower nearshore water temperatures rapidly, sometimes pushing them into the 60s even when air temperatures are extremely high.

Most recently, ocean temperatures near Asbury Park were about 70 degrees Fahrenheit, or 21 degrees Celsius. That is slightly above average for this time of year but remains within the normal seasonal range.

Many swimmers begin to consider the water warm when it rises above roughly 75 degrees. Peak ocean temperatures at the Jersey Shore typically occur from late August into early September because the ocean warms more slowly than the land.

What do the rock structures extending from Jersey Shore beaches actually do?

Structures built perpendicular to the beach are generally called groins. They interrupt the movement of sand along the shoreline and help maintain beach width in a particular area.

Jetties are similar structures built beside inlets. Their primary purpose is to stabilize an inlet and help prevent its navigation channel from shifting.

The terms are often used interchangeably in casual conversation, although the structures have different principal functions.

How do groins and jetties change the shape of a beach?

Sand moving along the coast tends to collect on the updrift side of a groin or jetty. The opposite side receives less sand and may become more vulnerable to erosion.

Because the dominant direction of sand movement changes near Long Beach Island, the pattern of accumulation also changes.

North of LBI, sand often builds up on the north side of a structure. South of LBI, it more often accumulates on the south side.

These patterns are another visible sign that the Jersey Shore is an active geological system, continually built, eroded and rearranged by the ocean.

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