“North Carolina beaches come in a variety of sizes, shapes and compositions. Some are wide and some narrow, some steep and others gentle, some have considerable shell content and some have no shells. If you revisit a beach over a period of time, you will find that the beach width changes and that the slope steepens or flattens in response to some seemingly invisible force of nature. If you know the right places to go you may find exposed tree stumps on the beach (Nags Head, Yaupon Beach), outcrops of mud layers (Topsail Island, Masonboro Island), or rocks on the beach (Fort Fisher). And although the bulk of the beach is composed of quartz sand and shell, examination of a particular beach may lead to the discovery of a Mastadon tooth or bone fragment (Onslow Beach), sharks’ teeth (Topsail Island), giant fossil oyster shells (Topsail Island), chunks of fossiliferous limestone (Shackleford Banks), or smooth, flat quartz pebbles (Nags Head). These fascinating beach forms, fragments, and fossils are clues to the history of the beaches and how they formed.”
—How to Read a North Carolina Beach, page 23.
Barrier island movement
Except for Kure Beach, which is part of the mainland, all of North Carolina’s beaches are on barrier islands. Over time, these islands respond to sea level changes by migrating, rolling over themselves somewhat like the tread of a bulldozer.
Sand
Most sand is made up of quartz and 10 to 15 percent crushed shells. The sand on dunes, because it is light enough to be blown by winds, is generally lighter than that on the beach.
“Grain size determines the slope of the beach. Beaches with finer sand grains tend to be flatter, with gentler slopes (between the high and low tide lines) than beaches with coarser grains. The reason for this has to do with the ability of sand to absorb water from wave swash. Fine sands absorb relatively little water, and so most of the water that flows up the beach flows back down the beach. This backwash tends to move the sand seaward and thus flatten the beach.” —How to Read a North Carolina Beach, pages 18-19.
Beach Terminology
Barking sand. Singing or barking occurs on most sand beaches of the world. It goes by a lot of names, including musical sand, whistling sand, squeaking sand and, in Japan, frog-sound sand…. In order for the sand to sing, all of the grains must be of similar size…. The sound is produced by the shear that occurs when one layer of sand grains slides over the layer beneath it, with all the grains moving in unison.
Black sand: Heavy-mineral concentrations or placers that form by the winnowing away (by wind or water) of the lighter sand grains. The black color typically comes from magnetite and ilmenite. Commonly mistaken for oil pollution.
Bubbly sand: Sand with an open, porous texture due to the entrapment of air bubbles within the beach.
Drift line: A mass of natural and artificial debris (e.g., seaweed, Spartina straw, fishing nets, lumber, driftwood, plastic bottles) indicating the previous landward extent of the high-tide line and/or wave swash.
Foredune: The dune closest to the beach.
Intertidal zone: The wet portion of the beach exposed at low tide. The zone between the low and high tides.
Longshore current: The current flowing parallel to a beach that is created by waves striking the coast at an angle.
Medaño: A large, solitary dune such as Jockey’s Ridge or Run Hill Dune that is created by winds blowing from several different directions.
Nail hole: An informal term for a hole in the beach that has the diameter of a nail. Such holes are produced by air escaping from the sand.
Overwash: Beach sand that has been transported inland beyond the beach by storm waves.
Ridge and runnel: The “ridge” of a ridge and runnel system is a sandbar. The “runnel” is the troughlike area between the ridge and beach.
Rill marks: Small erosional channels in the sand carved out by either fresh- or saltwater draining out of the beach sand at low tide. At the end of each rill the sand is deposited in small splays or microdelta-like features.
Salcrete: Layer of cohesive sand on the surface of the beach that sticks together due to cementation by salt crystals.
Scarp: A small sand cliff on the beach indicating rapid erosion.
Shell hash: Descriptive term for a concentration of broken shell material on a beach.
Swash mark: Line formed at the edge of swash advance when a wave breaks. As water soaks into the beach, the material being carried by the swash or floating on its edge is deposited to form the line.
Excerpts from How to Read a North Carolina Beach, by Orrin H. Pilkey, Tracy Monegan Rice and William J. Neal, pages 18, 19, 23, 101 and glossary. Published by the University of North Carolina Press, Chapel Hill (2004).
