Category Science

Beaches are made as rocks, worn away from headlands, are ground down into shingle and sand. The sea then deposits these particles in a sheltered place, forming a beach.

Rocks or coral reefs located off the shore are worn down by moving waves. As these materials are worn down, they become small particles of sediment that are carried by the waves in a state of suspension. In the case of sediment from further inland, the particles are washed to the larger body of water, where they are swept up by the waves and into the same state of suspension. These suspended particles cause the moving water to have increased erosive ability, resulting in greater amounts of eroded particles in the water.

In some cases, fish and other marine animals contribute to the speed of erosion. This is particularly true in beaches that are located near coral reefs. Many of these animals rely on algae growing on the coral as a major dietary supplement. As they eat away the algae, they inadvertently cause the coral to break off into small pieces. Some pieces may even work their way through the digestive tracts of these animals, resulting in even smaller particles that are washed up into the waves.

Erosion is typically thought to decrease the size of certain landforms, however, this is not always the case. In fact, erosion actually works to increase the size and width of some beaches. This growth occurs as the waves deposit the aforementioned sediment onto the land. Additionally, beaches may experience growth in size near river deltas, where rivers carry eroded sediment to the ocean. This sediment is deposited along the beach before being carried off into the ocean.

The type of wave that reaches the coastline also plays a part in the formation of beaches. Constructive waves, which are those that allow the water to recede and the beach particles to stop moving between waves, result in compacted sediment. This firm beach surface prevents future erosion. Destructive waves, which are fast forming and do not allow the water to recede between waves, result in a near-constant state of sediment suspension in the water. Because the particles remain in the waves, rather than being deposited on the shoreline, the beach in these areas is more likely to suffer from future erosion. With destructive waves, the sediment is not given a chance to settle and become compacted.

Picture Credit : Google

Perhaps the most dramatic coastlines are seen where rocky headlands have been eroded into arches and stacks. As the sea erodes the rocky coastline, only the toughest rocks remain, sometimes forming arch-shaped head-lands. Eventually, the roofs of these arches may fall, leaving tall, rocky columns known as sea stacks.

A stack or sea stack is a gelogical landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion. Stacks are formed over time by wind and water, processes of coastal geomorphology. They are formed when part of a headland is eroded by hydraulic action, which is the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to later collapse, forming free-standing stacks and even a small island. Without the constant presence of water, stacks also form when a natural arch collapses under gravity, due to sub-aerial processes like wind erision. Erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast—the stack. Eventually, erosion will cause the stack to collapse, leaving a stump. Stacks can provide important nesting locations for seabirds, and many are popular for rock climbing.

Isolated steep-sided, rocky oceanic islets, typically of volcanic origin, are also loosely called “stacks” or “volcanic stacks”.

Stacks typically form in horizontally-bedded sedimentary, or volcanic rocks, particularly on limestone cliffs. The medium hardness of these rocks means medium resistance to abrasive and attritive erosion. A more resistant layer may form a capstone. (Cliffs with weaker rock, such as claystone or highly jointed rock, tend to slump and erode too quickly to form stacks, while harder rocks such as grnite erode in different ways.)

The formation process usually begins when the sea attacks lines of weakness, such as steep joints or small fault zone in a cliff face. These cracks then gradually get larger and turn into caves. If a cave wears through a headland, an arch forms. Further erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast, the stack. Eventually, erosion will cause the stack to collapse, leaving a stump. This stump usually forms a small rock island, low enough for a high tide to submerge.

Picture Credit : Google

The strength of the sea is such that many coastlines are easily eroded. Caves and arches are created as the waves attack a headland from all sides. These features then continue to be eroded in two ways. Stones thrown up by the sea scrape away at the rocks, wearing the cliffs into the sea. Cracks in the rock are then made bigger as air forced into them by the water expands when the waves retreat.

Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of  wave currents tides wind-driven water, waterborne ice, or other impacts of storms. The landward retreat of the shoreline can measured and described over a temporal scale of tides, seasons, and other short-term cyclic processes. Coastal erosion may be caused by hydraulic action, abrasion impact and corrosion by wind and water, and other forces, natural or unnatural.

On non-rocky coasts, coastal erosion results in rock formations in areas where the coastline contains rock layers or fracture zones with varying resistance to erosion. Softer areas become eroded much faster than harder ones, which typically result in landforms such as tunnels, bridges, columns and pillars. Over time the coast generally evens out. The softer areas fill up with sediment eroded from hard areas, and rock formations are eroded away. Also abrasion commonly happens in areas where there are strong winds, loose sand, and soft rocks. The blowing of millions of sharp sand grains creates a sandblasting effect. This effect helps to erode, smooth and polish rocks. The definition of abrasion is grinding and wearing a way of rock surfaces through the mechanical action of other rock or sand particles.

Examples

A place where erosion of a cliffed coast has occurred is at Wamberal in the Central Coast region of New South Wales where houses built on top of the cliffs began to collapse into the sea. This is due to waves causing erosion of the primarily sedimentary material on which the buildings foundations sit.

Dunwich, the capital of the English medieval wool trade, disappeared over the period of a few centuries due to redistribution of sediment by waves. Human interference can also increase coastal erosion: Hallsands in Devon, England, was a coastal village washed away over the course of a year, 1917, directly due to earlier dredging of shingle in the bay in front of it.

The California coast, which has soft cliffs of sedimentary rock and is heavily populated, regularly has incidents of housing damage as cliffs erodes. Devil’s slide, Santa Barbara, the coast just north of Ensenada, and Malibu are regularly affected.

Picture Credit : Google

The world’s coastlines show more varicd feature than any other kind of landscape. The type and appearance of a coastline depends on the kind of rock present where the land meets the sea, as well as the strength and direction of the prevailing winds, tides and currents.

If you’ve ever been to the beach, you’ve been on a coast. The coast is the land along a sea. The boundary of a coast, where land meets water, is called the coastline.
 

Waves, tides, and currents help create coastlines. When waves crash onto shore, they wear away at, or erode, the land. But they also leave behind little parts of the sea, such as shells, sand dollars, seaweeds, and hermit crabs. Sometimes these objects end up as more permanent parts of the coastline.

Coastal changes can take hundreds of years. The way coasts are formed depends a lot on what kind of material is in the land and water. The harder the material in the land, the harder it is to erode. Coastlines of granite, a hard rock, stay pretty stable for centuries. Sugarloaf Mountain, on the coast of Rio de Janeiro, Brazil, is made mostly of granite and quartz. It has been a landmark for centuries.

The famous White Cliffs of Dover, in England, are made of calcium carbonate. This is a soft material and erodes easily. However, it exists in such great quantities that years of erosion have not made a visible impact on the coastline. The White Cliffs are a landmark of the English coast of the English Channel. (The other coast is French.)

Tides, the rise and fall of the ocean, affect where sediment and other objects are deposited on the coast. The water slowly rises up over the shore and then slowly falls back again, leaving material behind. In places with a large tidal range (the area between high tide and low tide,) waves deposit material such as shells and hermit crabs farther inland. Areas with a low tidal range have smaller waves that leave material closer to shore.

Waves that are really big carry a lot of energy. The larger the wave, the more energy it has, and the more sediment, or particles of rock, it will move. Coastlines with big beaches have more room for waves to spread their energy and deposits. Coastlines with small, narrow beaches have less room for waves to spread out. All the waves’ energy is focused in a small place. This gives the small beaches a tattered, weathered look. Sandy beaches are washed away, and rocky coastlines are sometimes cracked by strong waves.

Because coasts are dynamic, or constantly changing, they are important ecosystems. They provide unique homes for marine plants, animals, and insects. Coasts can be icy, like the Shackleton Coast of Antarctica, or desert, like the Skeleton Coast of Namibia.

Picture Credit : Google

Lakes may eventually disappear. This happens as they drain away through man-made barriers, fill up with sediment from rivers, or evaporate as the climate changes.

Bolivia’s second largest lake has vanished into thin air. In December, Lake Poopo became a dry salt pan and its largest lake – Lake Titicaca – is heading towards trouble, too. Recent research and new data suggest that lakes in other parts of the world may also be on their way out.

The combination of silting up and irrigation withdrawal from the Desaguadero River, which feeds Poopo, together with climate change and the extra warmth from current El Niño, were enough to finish this lake off. “Considering the size of the lake – 2700 square kilometres – this is quite an astounding event, with slim prospects of recovery,” says Dirk Hoffmann from the Bolivia Mountain Institute. “This event should serve as a real warning. Eventually, we can expect Lake Titicaca to go the same way.”

Air temperature has risen by around 0.7 °C in the Andes over the past 70 years and lakes are being evaporated faster than they are replenished. Lake Titicaca is close to a tipping point. Just 1 to 2 °C of atmospheric warming – which is expected by 2050 – could be enough to evaporate the top few metres, which would shut down the Desaguadero River and dry up all the water bodies that this river feeds. Such an outcome would be catastrophic for the 3 million inhabitants of Bolivia’s highlands, including the city of La Paz.

“If Titicaca stops supplying the Desaguadero River then the region will enter a new climate regime and the entire Andean Plateau will change from a benign agricultural area to an arid inhospitable area,” says Mark Bush, biologist at Florida Institute of Technology. “This happened during two prior interglacials and each time the dry event lasted for thousands of years.” It’s not just Andean lakes that are in trouble. Evidence from around the world suggests that lakes are warming, shrinking or disappearing, with huge impacts on ecosystems.

Picture Credit : Google