What Makes a Beach a Beach?


Beaches are dynamic systems of sand, water, flora, and fauna that constantly shift and change. Their allure, however, is enduring. As destinations for swimming and body surfing, meeting with friends and relaxing, and watching romantic sunsets, our beaches offer myriad moments of pleasure.

 

So … what makes a beach a beach? Sand along the coast. (Duh.) Sand at our beaches is a mix of beige quartz, some darker minerals, and coral fragments from nearby reefs. Each beach is comprised of a unique combination of grains — size, shape, sorting, color and composition can all vary — and the vegetation that washes ashore. Despite these potentially infinite combinations, most beaches share common features. As you move toward shore, you’ll probably find:

  • Terraces and dunes of the backshore (or backbeach), ideal for cabanas, lounge chairs, and football. Terraces are flat and may slope slightly landward, and this area remains dry except during large storms. Because wind transports sand in these areas, ripples may form. Also, wind carries away smaller sand grains, leaving surface of coarser (i.e., larger) grains and shell fragments.
  • The crest of a low berm that rises above the high-tide line marking a transition from backshore to foreshore (or forebeach, or beach face).
  • A smooth beach face that slopes toward the water forming the front part of the low berm. Because it includes the swash zone, it makes an excellent path to walk along (like at Dorada Beach).
  • Swash and surf zones:
  • Swash zone, where water and sediment uprush and backwash after waves crash. On steep beaches, runnels may form to channel the backwash.
  • Surf zone (or breaker zone), where wave energy from the deep ocean is compressed in shallower water, causing the waves to break. The fun zone (like at Juan Dolio Beach).

As tide rises, these zones move higher up the beach face, only to fall back as the tide recedes.

  • The base of the beach face is marked by a small ridge or beach step that is coarser-grained, where backwash meets crashed waves, creating a narrow high-energy zone. As backwash extends beyond the beach step, seaward rip currents can form in the same area that waves break, creating potentially dangerous conditions.

 

In the upper swash zone, sand grains are deposited as water energy dissipates. Backwash will carry these sand grains away but, because backwash moves slower than uprush, mostly lighter-weight and lighter-colored minerals will be carried back out, leaving heavier and darker minerals behind. The difference is most pronounced at the high-water line (that is, the landward extent of the swash zone at high tide), which can be spotted by an increase in beach slope, and a thin sinuous line of black (or dark) sand grains.

Dorada0387

Some beaches are carved into a series cusps or arcs that are remarkably symmetrical and even. The tips that extend seaward are coarser-grained and their accompanying embayments have finer-grained (and softer) sand and mud. At beaches with smaller cusps, the shore seems like a series of regularly-spaced, very gentle dunes.

 

And now that there’s a beach …

Tom Pacioni

Tom Pacioni

Sustainability and environmental professional with a love of the beach. Tom studied coastal and nearshore depositional processes (MS Geology), and worked in Incident Command during the Deepwater Horizon spill and recovery. Spent a couple decades solving environmental and hydrogeology issues along the Gulf Coast as a Professional Geologist. Currently wrapping up a Sustainability Management MS at Columbia University.

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