Geography
Coastal Erosion Landforms
Coastal erosion landforms are physical features created by the gradual wearing away of coastal areas by natural forces such as waves, currents, and wind. Examples of coastal erosion landforms include sea cliffs, wave-cut platforms, and sea arches. These landforms are constantly changing due to the dynamic nature of coastal erosion processes.
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12 Key excerpts on "Coastal Erosion Landforms"
eBook - PDF- Timothy Foresman, Alan H. Strahler(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
2. Describe thedepositionallandformsproduced bywaves. 3. Define coastlinesofsubmergence. 4. Explain thefeaturesofcoralreefs. coastline(coast) The zone in which coastal processes op- erate or have a strong influence CoastalLandforms409 by as much as 125 m (410 ft). Rivers cut canyons to depths well below present sea level to reach the ocean. Waves broke against coastlines that are now well underwater. Now that sea level has risen, many coastal landscapes are coastlines of submergence. Still other coastlines are dominated by coral reefs, where ocean waters are warm enough for coral to grow. Erosional Coastal Landforms The breaking of waves against a shoreline provides a va- riety of distinctive features. Where resistant rocks meet the waves, sea cliffs often oc- cur. At the base of a sea cliff is a notch, formed largely by physical weathering. Constant splashing by waves followed by evaporation causes salt crystals to grow in tiny crevices and fissures of the rock, breaking it apart, grain by grain. Hydraulic pressure of waves and abrasion by rock fragments thrust against the cliff also erode the notch. Undercut by the notch, blocks fall from the cliff face into the surf zone. As the cliff erodes, the shoreline gradually retreats shoreward. Sea cliff erosion forms a variety of ero- sional landforms, including sea caves, sea arches, and sea stacks (Figure 13.18). zone in which waves perform their work, as well as the landforms they create. In contrast, the shoreline refers to the dynamic zone of con- tact between water and land. The Earth’s coastlines are enormously varied. For ex- ample, along most of the east coast of the United States, we find a coastal plain gently sloping toward the sea, with shallow lagoons and barrier islands at the coastline. On the west coast, we often find rocky shorelines, with dra- matic sea cliffs, headlands, and pocket beaches. Plate tectonics provides a way to explain these dif- ferences.
eBook - PDF- James Petersen, Dorothy Sack, Robert Gabler, , James Petersen, Dorothy Sack, Robert Gabler(Authors)
- 2014(Publication Date)
- Cengage Learning EMEA(Publisher)
Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 461 C O A S T A L D E P O S I T I O N (a) (b) (c) (d) (e) ■ FIGURE 17.14 Examples of landforms created by wave erosion. (a) A notch exposed near the base of basaltic sea cliffs in Hawaii. (b) A sea cave carved in limestone along Italy’s Mediterranean Sea coast. (c) A sea arch in Alaska. (d) An abrasion platform carved on steeply dipping sedimentary rocks, central California, partially exposed at low tide. (e) A marine terrace, the wide, beveled plain atop this eroding coastline. What other coastal erosional landforms do you see in photo (e)? D. Sack D. Sack J. Petersen Robert Cameron/Getty Images NOAA Image Library Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. C H A P T E R 1 7 • C O A S TA L P R O C E S S E S A N D L A N D F O R M S 462 Coastal Depositional Landforms The most common landform of coastal deposition is the beach , a wave-deposited feature that is contiguous with the mainland throughout its length ( ■ Fig. 17.15). Many beaches are sandy, but beaches of other grain sizes are also common, as for example, the cobble beach discussed earlier in the sec-tion on coastal erosion. In settings with high wave energy, particles tend to be larger and beaches steeper than where wave energy is low. Beach sediments come in a variety of col-ors depending on the rock and mineral types represented. Tan quartz, black basalt, white coral, and even green olivine beaches exist on Earth.
eBook - PDF- Vijay K. Sharma(Author)
- 2010(Publication Date)
- CRC Press(Publisher)
307 11 Coastal Processes and Landforms A coast is up to a few kilometers wide tract of interacting terrestrial and marine pro-cesses between the shoreline and landward limit of the first major change in terrain, usually in the form of a cliff or coastal dunes. Coastal geomorphology explains the contemporary processes and their landforms, translates the effect of global sea level changes of the Pleistocene and Holocene periods and of the tectonic instability of land-mass on the evolution of coastal landscape, and interprets the chronology of Quaternary events for the present state of coastal development. In brief, coastal geomorphology is concerned essentially with the physics of wave motion, hydraulics, sediment transport mechanisms, and interpretation of the environmental change (Kidson, 1968). GRADATIONAL PROCESSES Coasts are areas of incessant motion of shallow seawater against the littoral tract that varies much in lithology, geologic structure, and resistance to erosion. The coastal water moves onshore and offshore by the effects of waves, tides, and currents—the three process domains of marine erosion and deposition. In a general term, waves are destructive in storm conditions, tides are known more for constructive than destruc-tive work, and currents possess much less erosive potential. Tsunamis are a type of destructive waves, which develop by sudden dislocation of the seabed. W AVES Transfer of the wind energy onto the surface of a deep water body generates surface waves, such that the wave size depends directly on the wind speed, duration of time the wind blows from one direction, and extent of the open water, called fetch of the water surface, over which the wind blows prior to reaching a given observation point. These deep water waves are sinusoidal in form with interdependent length, height, amplitude, and period attributes.
No longer available |Learn more- James Petersen, Dorothy Sack, Robert Gabler(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
Other clasts are transported by waves and cur- rents in the coastal zone, being deposited when energy decreases and, if accessible, re-entrained when wave energy increases. The same is true of the second major source of coastal sediment, coastal cliff erosion. Of less importance is sediment brought to the coast from offshore sources. Although we may tend to think of sand-sized sediment when we think of coastal deposits, coastal depositional landforms may be composed of silt, sand, or any size classes of gravel from granules and pebbles through cobbles and boulders. The most common landform of coastal deposition is the beach, a wave-deposited feature that is contiguous with the ● FIGURE 20.15 Some of the major landforms found along erosion-dominated coastlines. Beach Sea cliff Marine terraces Embayment Headland Sea cave Sea arch Sea stack Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. C H A P T E R 2 0 • C O A S T A L P R O C E S S E S A N D L A N D F O R M S 582 ● FIGURE 20.16 Examples of landforms created by wave erosion. (a) A notch exposed near the base of basaltic sea cliffs in Hawaii. (b) A sea cave carved in limestone along Italy’s Mediterranean Sea coast. (c) A sea arch in Alaska. (d) Sea stacks along a cliffed coast. (a) D.Sack (b) Jim Petersen (c) NOAA Image Library (d) Richard Price/The Image Bank/Getty Images Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
eBook - PDF- Alan H. Strahler(Author)
- 2013(Publication Date)
- Wiley(Publisher)
As the cliff erodes, the shoreline gradually retreats shoreward. Sea cliff erosion results in a variety of erosional landforms, including sea caves, sea arches, and sea stacks (Figure 16.16). © 2012 Alex S. MacLean/Landslides 16.15 Retreating shoreline This marine scarp of Ice Age sediments at Mohegan Bluffs, Block Island, Rhode Island, is undergoing rapid erosion from wave action. This historic photo shows the Southeast Lighthouse being threatened by the cliff retreat; the lighthouse has now been moved to a safer spot, about 75 m (about 250 ft) from its previous location. EYE ON THE LANDSCAPE What else would the geographer see? The sediments exposed in the bluff were laid down by streams fed by melting stagnant continental ice sheets at the end of the Ice Age. Because the ice melted irregularly, the deposits are not very uniform, and the exposed bedding A gives that impression. The larger rocks in the depos- its, let down from melting ice, were too large to be moved by the streams laying the sediments. A large lag deposit B of these stones remains at the water’ s edge, where it is being worked by waves. A B Coastal Landforms 539 16.16 Erosion of a marine cliff Erosion of a marine cliff produces landforms such as shore platforms and sea stacks. Arthur N. Strahler Arch Shore platform Stacks Notch Cave 1 Weathering by salt-crystal growth and wave action undercuts the sea cliff or headland, forming a notch at the base of the cliff. 2 Weathering and erosion excavate the notch farther in a weak rock layer to form a sea cave. 3 When a headland is attacked from both sides, the notches connect to create a passage through the headland. Weathering and wave action enlarge the opening, creating a sea arch. 4 Finally, the top of the arch collapses, forming sea stacks that are remnants of the former headland.
eBook - PDF- Alan F. Arbogast(Author)
- 2017(Publication Date)
- Wiley(Publisher)
If the top of the arch collapses, an isolated sea stack remains, such as the one to the left. Note the tilted rock strata. 450 CHAPTER 19 Coastal Processes and Landforms Depositional Coastlines We have just seen how coastlines are shaped by erosion and some of the diagnostic landforms that result from this process. Now, let’s turn to the coastal landforms created when sediment is deposited in various ways and places. You were briefly intro- duced to this concept with the formation of a pocket beach be- tween two eroding headlands (Figure 19.14c). Coastlines in the process of extending outward into the water through deposi- tion are said to be undergoing progradation. Beaches The part of the coastal landscape people are probably most familiar with is the beach. Beaches are dynamic places where sediment is deposited through the combination of waves, beach drift, and wind. In some places, beaches are supplied with alluvial sands derived from land far inland. The beach is a transition between the water and the landmass and consists of exposed, unconsolidated sediments that usually range from sand to cobbles. Although finer silt and clay-sized particles are sometimes contained within a beach, they are usually carried away in suspension by the longshore current. Most beach growth occurs during the summer months in the Northern Hemisphere when the weather is relatively calm. In winter, however, beaches can be significantly eroded due to large waves created by strong storms. If you happen to live on or near a beach, notice how the shape of the beach can change between seasons. Figure 19.21 shows how beach components are differenti- ated on the basis of their relative position to the water. The offshore is permanently submerged and is the zone where waves break and the surf is most active.
eBook - PDFOceanography
An Invitation to Marine Science
- Tom Garrison(Author)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
Coasts are classified as erosional coasts (on which erosion dominates) or deposi-tional coasts (on which deposition dominates). Natural rock bridges, tall stacks, and sea caves are found on erosional coasts. Depositional coasts often support beaches, accumulations of loose particles. Generally, the finer the particles on the beach, the flatter its slope. Beaches change shape and volume as a function of wave energy and the balance of sediment input and removal. Coral reefs and estuaries are among the most complex and biologically productive coasts. Hu-man interference with coastal processes has generally accelerated the erosion of coasts near inhabited areas. In the next chapter you’ll learn that the study of oceanogra-phy includes a marvelous variety of living things. The next chapter’s discussion of the general nature and characteristics of marine life will launch us into the biological part of our journey. Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. CHAPTER 12 366 1. I have seen photos of the massive coastal modifications being made in Dubai. What happens when humans modify a coast-line so extensively? The Persian Gulf Emirate of Dubai has embarked on the most extensive human-made coastal developments in the world (Fig-ure 12.38) . Most of the additions were islands shaped like palm trees to maximize waterfront footage. Construction of the first island, Palm Jumeirah, began in June 2001. Shortly after, the Palm Jebel Ali was announced and reclamation work began.
eBook - PDF- James Petersen, Dorothy Sack, Robert Gabler, , James Petersen, James Petersen, Dorothy Sack, Robert Gabler(Authors)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
583 2 0 - 3 C O A S T A L G E O M O R P H I C P R O C E S S E S of wave action, they become marine terraces (Fig. 20.17b). Successive periods of uplift can create a coastal topography of marine terraces that resembles a series of steps. Each step rep- resents a period of time that a terrace was at sea level. The Palos Verdes peninsula just south of Los Angeles has perhaps as many as 10 marine terraces, each representing a period of platform formation separated by episodes of uplift. Rates of coastal erosion are controlled by the interaction between wave energy and rock type. Coastal erosion is greatly accelerated during high-energy events, such as severe storms and tsunamis. Human actions can also accelerate coastal erosion rates. We commonly do so by interfering with coastal sediment and vegetation systems that would naturally pro- tect some coastal segments from excessive erosion rates. We explore the nature of coastal depositional systems next. 20-3c Coastal Deposition Significant amounts of sediment accumulate along coasts where wave energy is low relative to the amount or size of sediment sup- plied. Embayments and settings where waves break at a distance from the shoreline, such as areas with gently shelving underwater topography, tend to sap wave energy and encourage deposition. Amount and size of sediment supplied to the coastal zone vary with rock type, weathering rates, and other elements of the cli- matic, biological, and geomorphic environment. Sediment within coastal deposits comes from three principal sources. Most of it is delivered to the standing body of water by streams. At its mouth, the load of a stream may be deposited for the long term in a delta or within an estuary, a biologically very productive embayment that forms at some river mouths where salt and fresh water meet. Elsewhere, stream load may instead be delivered to the ocean or lake for continued transportation.
eBook - PDFPhysical Geography
Great Systems and Global Environments
- William M. Marsh, Martin M. Kaufman(Authors)
- 2012(Publication Date)
- Cambridge University Press(Publisher)
9 Describe the three-step process of bank erosion. How are bedrock and softer shorelines eroded, and what shoreline features result in each setting? 10 What are sediment sources and sediment sinks and how are they linked together to form a system? What name is give to such systems and what does it mean if a system has a large net sediment transport value? 11 What explains the occurrence of deposition zones or sites, along a shoreline? Using Figure 22.25, identify the landforms associated with these sites: coastal island, mouth of a bay, head of a bay, and explain why they formed there. 12 At the global scale, how do plate tectonics influence coastline development? What are the differences between active and passive coasts in terms of their formative processes and landforms? 13 Using Figures 22.31 and 22.32 as a guide, identify the primary landforms associated with emergent and submergent coasts. What are the distinct roles of plate tectonics, glaciation, and deposition within each type of coast? 14 Name three structures commonly used in coastal engineering, what they are designed to do, and the nature of the problems they often create. 15 In the 21st century struggle between humanity and the sea, the outcomes will be different for different countries. Discuss several of the factors that will shape these outcomes. Glaciers have became media causes celebres because they are considered harbingers of a changing global climate, and rightly so. To form and survive, glaciers need cold temperatures and plenty of snow, and when one or both of these changes on an established glacier, it grows or shrinks, and lately glaciers the world over have been shrinking not because of too little snow but because of warmer temperatures. And when we look back over the past two million years or so in Earth history, we find concrete evidence of distinct patterns of glaciers growing and shrinking in response to changes in climate.
eBook - PDFPhysical Geology
The Science of Earth
- Charles Fletcher(Author)
- 2017(Publication Date)
- Wiley(Publisher)
A submerging coast is any place where the net result of sea level change and vertical land movement is marine drowning. In the current era of accelerated sea level rise, many coastal systems are submerging. These include areas where estuaries form in the flooded mouths of river systems, such as along the eastern coast of the United States (e.g., Chesapeake Bay, shown in Figure 20.30). In places where great volumes of sediment collect, such as major delta regions, the enormous weight of the sediment causes downward flexing of the lithosphere. When a rise in sea level is added to this subsidence, rapid flooding occurs across broad expanses of low-lying shoreline. The Ganges– Brahmaputra river delta region is an example of a submerging coast. This region, on the coast of Bangladesh, one of the world’s poorest countries, is expected to undergo a rise of 1.5 meters in sea level in response to the combination of global warming and submergence. It is estimated that the nation will lose 16% of its land area and that 15% of its population will be displaced. Erosional and Depositional Coasts Another way to classify coastal systems is by the net result of physical processes, either erosional or depositional. Erosional coasts are those that are experiencing net land- ward migration under the force of erosion. Most often they include rocky shorelines undergoing landward retreat. Sea stacks, wave-cut benches, and undercut cliffs characterize erosional coasts. Erosional coasts typically have steep topography asso- ciated with tectonically active margins, with a narrow continental shelf, steep coastal plains, and “youthful” mountain systems—those that have not existed long enough to shed high volumes of sediments. Rivers tend to cut Coasts May Be Submergent or Emergent, Depositional or Erosional, or Exhibit Aspects of All Four of These Characteristics 639 into steep mountainous watersheds with high gradients.
eBook - PDF- David Huddart, Tim A. Stott(Authors)
- 2019(Publication Date)
- Wiley-Blackwell(Publisher)
Consequently the rate of erosion will fall. 19.5.1.3 Abrasion The scouring effect of water charged with sand or shingle will abrade a cliff as it impacts and shears past it. Sunamara (1977) illustrated this point with one of his physical wave‐tank models, where he showed the rate of cliff erosion within the wave tank with time against the size of the beach formed by the eroded debris. Initially erosion is negligible since there is lit- tle abrasive sediment within the water. As a small beach builds up as erosion proceeds, the rate of ero- sion accelerates, since the beach provides a ready source of abrasive sediment for the breaking waves. In time, the beach builds up sufficiently to buffer the cliff from the waves and the rate of erosion declines. 19.5.1.4 Corrosion Solution of calcareous rock, such as limestone or chalk, may be a significant erosional process on some cliffs, particularly within warmer climates. It has been proposed that the form of the coastal zone in limestone regions could be classified according to temperature and tidal range, describing four main types of coastal limestone landform. In cool temper- ate regions, such as on the Carboniferous limestone of South Wales, or in southern Ireland, the spray zone is pitted by small corrosion hollows a few millimetres in depth and <5 mm in width. Lower down the platform, as the frequency of inundation increases, there are solution pools per- haps 10–30 cm deep, whilst towards the low water mark sharp pinnacles or lapies (marine karren) coexist with pools. These lapies have formed by solution of rock by running or standing water. In warm tidal seas, jagged lapies are found further up the platform in the spray zone, whilst vasques, which are shallow, flat‐bottomed pools forming networks organized into a series of terrace‐like steps, occur in the upper portions of the intertidal zone and become overdeepened with overhanging sides seawards.
No longer available |Learn more- Donald Hyndman, David Hyndman(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
Others have become year-round dwellings for urban retirees. By 2004, approxi- mately 42% of the population of the continental United States lived in coastal counties. Coastal populations continue to grow. For example, the population of Florida increased by approximately 50% from 1990 to 2013. Beaches and sea cliffs constantly change with the seasons and progressively with time. When people build permanent structures at the beach, coastal processes do not stop; the processes interact with and are affected by those new struc- tures. Instead of living with the sea and its changing coast- line, people try to hold it back and prevent natural changes to the beaches and sea cliffs. Hurricanes and their dramatic aftermaths are often viewed as abnormal or “nature on a rampage.” In fact, they are nor- mal for a constantly evolving landscape. What is abnormal is how human actions and structures cause natural processes to impose unwanted damage. To be aware of coastal haz- ards, we need to understand wave processes and the forma- tion of beaches and sea cliffs. We also need to understand how human activities affect wave action, beach response, and sea-cliff collapse. Waves and Sediment Transport Winds blowing across the sea push the water surface into waves because of friction between air and water. Wind- driven waves are described in terms of wave height, wave- length, and period (FIGURE 15-1). Gentle winds form small ripples. As the wind speed increases, ripples grow into waves that grow higher as they catch even more of the wind energy, somewhat like a sail. Two other factors that increase wave height are fetch, which is the length of water surface over which the wind blows, and the amount of time the wind blows across the water surface. Ocean waves are generally much larger than those on lakes, and prolonged storms often build huge, damaging waves.
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