Beaches: Sand, Surf and Foam

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Sandwood Bay, Scotland
Beaches are landform alongside bodies of water made up loose particles such as sand, gravel, pebbles, rocks or even biological sources, such coralline algae or as mollusc shells. The character and look of beach — in terms of textures, colors and gradients or layers of material — is influenced by things like sediment settlement patterns, often determined by densities and structures of the materials, and local wave action and weather. [Source: Wikipedia]

Though beaches can be found around inland freshwater lakes and rivers, they are mostly associated with coastal areas of the oceans and seas where waves or currents deposit and rework sediments. Erosion and other conditions that can change a beaches make up happens through natural processes such a wave action and extreme weather events. Under the right wind conditions coastal dunes can form.

Sandy beaches occupy about one third of global coastlines. Many are utilized for recreation and , have important economic and cultural roles by attracting swimmers, surfers, tourists and the like. Human impact on beaches has been significant in terms of infrastructure and the construction of resorts, camps, hotels, restaurants and beach houses and through water pollution, plastic pollution and coastal erosion from sea level rise and climate change. Natural forces that alter beaches have become more extreme due to climate change. Some scientists have predicted as much as 50 percent of the earth's sandy beaches will disappear by 2100 due to climate-change-driven sea level rise.

Websites and Resources: National Oceanic and Atmospheric Administration (NOAA); “Introduction to Physical Oceanography” by Robert Stewart , Texas A&M University, 2008 ; Woods Hole Oceanographic Institute ; Cousteau Society ; Monterey Bay Aquarium


Apollo Beach, Victoria, Australia

Ocean sand is not created by crashing surf but rather its generated by land-based pebbles being ground into smaller and smaller grains and these are carried by rivers out to sea — and by coral-munching fish such as parrotfish. Huge waves generated by hurricanes, typhoons and winter storms can destroy a sand beach in as little as a few hours. The environmentalist Rachel Carson wrote, "In every curving beach, in every grain of sand, there is a story of the Earth." Every you take a step in the sand you are quashing around 30,000 organisms. These include microscopic worms, crustaceans and bizarre-looking microscopic creatures.

Sand is nothing more than tiny rocks. In the United States it is defined as particles between .05 and 2 millimeters in diameter. Smaller particles are called silt or clay. Larger fragments are gravel. All sand was formed by breaking of rocks through the action of water, ice or air. The history of sand can be ascertained by examining it under a microscope: angular particles were created by glaciers; round grains have been weathered by wind or water

Sand (and sandpaper) is broken down into five categories: 1) very coarse (2 to 1 millimeters in diameter); 2) coarse (1 to .5 millimeters in diameter); 3) medium (.5 to .25 millimeters in diameter); 4) fine (.25 to .1 millimeters in diameter); 5) very fine (.1 to .05 millimeters in diameter).

Scientists still don’t understand why piles of sand tend to “avalanche” until they reach a certain slope. Jetties and groins created to keep sand from being washed away merely trap it one area and prevent it from spreading to someplace else. In the United States the U.S. Army Corps of Engineers spends $2 billion a year to replenish land.


Sand Composition

Sand is usually composed or hard minerals such as quartz that cannot be broken down into silt or clay. Yellow, brown and reddish shades of sand indicate there presence of iron compounds. Red sand is composed of quartz coated by a layer of iron oxide. White sands are nearly pure gypsum. Sand with a high percentage of silicate can be used in glassmaking.

Sand from Third Beach, Vancouver

The tan color of most sand beaches is the result of iron oxide, which tints quartz a light brown, and feldspar, which is brown to tan in its original form. Black sand comes from eroded volcanic material such as lava, basalt rocks, and other dark-colored rocks and minerals, and is typically found on beaches near volcanic activity. Black-sand beaches are common in Hawaii, the Canary Islands, and the Aleutians. [Source: NOAA]

The by-products of living things also play an important part in creating sandy beaches. Bermuda's preponderance of pleasantly pink beaches results from the perpetual decay of single-celled, shelled organisms called foraminifera.

Quicksand is sand that is so saturated with water it can not support any weight. Sandstone is created by sand, mixed with lime, chalk or some other material that acts as a binding agent, that is deposited in layers at the bottom of a sea or other area and pressed together into rock by the great pressure of sediments that are deposited on top if it over thousands or millions of years. The rock appears on the surface due to mountain-building forces and erosion.

Sand Creation

Sand is the end product of many things, including decomposed rocks, organic by-products, and even parrotfish poop. It comes from many locations, sources, and environments. Sand forms when rocks break down from weathering and eroding over thousands and even millions of years. Rocks take time to decompose, especially quartz (silica) and feldspar. [Source: NOAA]

Often starting thousands of miles from the ocean, rocks slowly travel down rivers and streams, constantly breaking down along the way. Once they make it to the ocean, they further erode from the constant action of waves and tides.

David Attenborough wrote: Sand "is all that remains of desert rocks after thousands of years of being grilled by the sun during the day and chilled to freezing point at night, Under such conditions even the most durable granite begins to crack and flake. Slowly it disintegrates into its constituent minerals. Each grain, as it is hurled repeatedly against the cliffs by the wind, blown over flat rocky pavements and rubbed against other grains, becomes round."

Less common but no less inviting beaches, devoid of quartz as a source of sand, rely on an entirely different ecologic process. The famous white-sand beaches of Hawaii, for example, actually come from the poop of parrotfish. The fish bite and scrape algae off of rocks and dead corals with their parrot-like beaks, grind up the inedible calcium-carbonate reef material (made mostly of coral skeletons) in their guts, and then excrete it as sand. At the same time that it helps to maintain a diverse coral-reef ecosystem, parrotfish can produce hundreds of pounds of white sand each year!

Parrotfish, Algae and Sand

Parrotfish discharging sand

"Coral eating" fish such as parrotfish feed on the algae rather than the coral polyps themselves. Many do this by eating the rocky coral itself, extracting the food the need and grinding up rocky material and expelling it as sand. The source of much of the recently made sand sediments around the reef is from parrotfish and other coral eaters. Not all coral-eaters use this method. The leatherjacket is bright green fish with orange spots. It feeds on coral by clamping its mouth around the entrance of a polyps chamber and sucking out the polyp.

Parrotfish use fused tooth plates in their beak and a gristmill in their throat to chisel off and pulverize reef rock to get nutrients from algae that coat and bore into coral. This can keep coral from being suffocated by algae allowed to grow unchecked, but on the other hand overgrazing by the fish can destroy corals.

According to the University of Hawaii: Parrotfish have unique teeth that allow them to play an integral role on coral reefs, especially in the Caribbean and Indo-Pacific. Parrotfish teeth are fused together This fusion enables them to scrape off fine, filamentous algae that grow within coral skeletons and on dead coral substrates. During this scraping while foraging for algae, parrotfish often ingest chunks of coral. Parrotfish have a special set of toothplates in their throat called a pharyngeal mill (pharyngeal = relating to the pharynx or throat) that acts like additional teeth to assist in grinding up the hard coral. The ground-up coral is passed through their digestive tract and expelled as fine-grain white sand The sand that is produced by parrotfish forms beaches and provides valuable habitat for benthic organisms like crabs and shrimp.

Surf — Coastal Waves

According to the “Introduction to Physical Oceanography”: “Wave phase and group velocities are a function of depth when the depth is less than about one-quarter wavelength in deep water. Wave period and frequency are invariant (don’t change as the wave comes ashore); and this is used to compute the properties of shoaling waves. Wave height increases as wave group velocity slows. Wave length decreases. Waves change direction due to refraction. Finally, waves break if the water is sufficiently shallow; and broken waves pour water into the surf zone, creating long-shore and rip currents. [Source: Robert Stewart, “Introduction to Physical Oceanography”, Texas A&M University, 2008]

Because wave velocity is a function of depth in shallow water, variations in offshore water depth can focus or defocus wave energy reaching the shore. Consider the simple case of waves with deep-water crests almost parallel to a straight beach with two ridges each extending seaward from a headland.

Big waves

Wave group velocity is faster in the deeper water between the ridges, and the wave crests become progressively deformed as the wave propagates toward the beach. Wave energy, which propagates perpendicular to wave crests, is refracted out of the region between the headland. As a result, wave energy is focused into the headlands, and breakers there are much larger than breakers in the bay. The difference in wave height can be surprisingly large. On a calm day, breakers can be knee high shoreward of a submarine canyon at La Jolla Shores, California, just south of the Scripps Institution of Oceanography. At the same time, waves just north of the canyon can be high enough to attract surfers.

Waves break in a narrow band of shallow water along the beach, the surf zone. After breaking, waves continues as a near-vertical wall of turbulent water called a bore which carries water to the beach. At first, the bore surges up the beach, then retreats. The water carried by the bore is left in the shallow waters inside the breaker zone.

Breaking Waves

According to the “Introduction to Physical Oceanography”:As waves move into shallow water, the group velocity becomes small, wave energy per square meter of sea surface increases, and nonlinear terms in the wave equations become important. These processes cause waves to steepen, with short steep crests and broad shallow troughs. When wave slope at the crest becomes sufficiently steep, the wave breaks. The shape of the breaking wave depends on the slope of the bottom, and the steepness of waves offshore.[Source: Robert Stewart, “Introduction to Physical Oceanography”, Texas A&M University, 2008]

1) Steep waves tend to lose energy slowly as the waves moves into shallower water through water spilling down the front of the wave. These are spilling breakers. 2) Less steep waves on steep beaches tend to steepen so quickly that the crest of the wave moves much faster than the trough, and the crest, racing ahead of the trough, plunges into the trough. 3) If the beach is sufficiently steep, the wave can surge up the face of the beach without breaking in the sense that white water is formed. Or if it is formed, it is at the leading edge of the water as it surges up the beach. An extreme example would be a wave incident on a vertical breakwater.

Steep, plunging breakers are the archetypical breaker. The edge of such breakers are ideal for surfing. Edge waves are produced by the variability of wave energy reaching shore. Such waves exist in the breaker zone near the beach and on the continental shelf.

Waves tend to come in groups, especially when waves come from distant storms. For several minutes breakers may be smaller than average, then a few very large waves will break. The minute-to-minute variation in the height of breakers produces low-frequency variability in the along-shore current. This, in turn, drives a low-frequency wave attached to the beach, an edge wave. The waves have periods of a few minutes, a long-shore wave length of around a kilometer, and an amplitude that decays exponentially offshore.

Sea Foam

Beach foam in the North Sea

Sea foam forms when dissolved organic matter in the ocean is churned up. If you scoop up some water from the ocean in a clear glass and look at it closely, you'll see that it's chock full of tiny particles. Seawater contains dissolved salts, proteins, fats, dead algae, detergents and other pollutants, and a bunch of other bits and pieces of organic and artificial matter. If you shake this glass of ocean water vigorously, small bubbles will form on the surface of the liquid. [Source: NOAA]

Sea foam forms in this way — but on a much grander scale — when the ocean is agitated by wind and waves. Each coastal region has differing conditions governing the formation of sea foams. Algal blooms are one common source of thick sea foams. When large blooms of algae decay offshore, great amounts of decaying algal matter often wash ashore. Foam forms as this organic matter is churned up by the surf.

Most sea foam is not harmful to humans and is often an indication of a productive ocean ecosystem. But when large harmful algal blooms decay near shore, there are potential for impacts to human health and the environment. Along Gulf coast beaches during blooms of Karenia brevis, for example, popping sea foam bubbles are one way that algal toxins become airborne. The resulting aerosol can irritate the eyes of beach goers and poses a health risk for those with asthma or other respiratory conditions. Scientists studying the cause of a seabird die-offs off California in 2007 and in the Pacific Northwest in 2009 also found a soap-like foam from a decaying Akashiwo sanguinea algae bloom had removed the waterproofing on feathers, making it harder for birds to fly. This led to the onset of fatal hypothermia in many birds.

Ocean Etiquette

Marine Wildlife Viewing Guidelines:
1) Learn before you go. Read about the wildlife, viewing sites, and local regulations to get the most from your wildlife viewing experience.
2) Keep your distance. Use binoculars, spotting scopes, and cameras with zoom lenses to get a closer look.
3) Hands off. Never touch, handle, or ride marine wildlife. Touching wildlife, or attempting to do so, can injure the animal, put you at risk, and may also be illegal for certain species.
4) Do not feed or attract wildlife. Feeding or attempting to attract wildlife with food, decoys, sound, or light disrupts normal feeding cycles, may cause sickness or death from unnatural or contaminated food items, and habituates animals to people. [Source: NOAA]

5) Never chase or harass wildlife. Never completely surround the animal, trap an animal between a vessel and shore, block its escape route, or come between mother and young.
6) Stay away from wildlife that appears abandoned or sick. Some marine animals, such as seals, leave the water or are exposed at low tide as part of their natural life cycle — there may be nothing wrong with them. If you think an animal is in trouble, contact local authorities for advice or report it to the NOAA Fisheries stranding network.

Beach zones

Reef Tips for Divers, Snorkelers and Swimmers:
1) Maintain natural buoyancy to avoid knocking or brushing against coral and marine life.
2) Coral is alive and easily damaged. Avoid touching, grabbing or standing on coral.
3) Please watch your fin wash. Sand can injure or smother small creatures and coral.
4) The underside of rocks are home to small creatures that can not live anywhere else. Please leave rocks, shells and coral in place for the reef dwellers who need them.
5) Killing, damaging, riding or chasing are examples of poor diver behavior.
6) Trash can kill marine life. Please collect any trash you see on the beaches or in the water.
7) Feeding fish can make them pests, and some may even aggressive toward divers.
8) Use a permanent mooring buoy to secure your boat instead of dropping an anchor.
9) Do not collect live shells.

Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); “Introduction to Physical Oceanography” by Robert Stewart , Texas A&M University, 2008 ; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023

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