Geography
Coastal Erosion and Deposition
Coastal erosion refers to the process of wearing away and removal of land or rock along the coastline by the action of waves, currents, and tides. Deposition, on the other hand, involves the accumulation of sediments and materials along the coast, often resulting in the formation of beaches, spits, and barrier islands. These processes play a crucial role in shaping coastal landscapes.
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11 Key excerpts on "Coastal Erosion and Deposition"
eBook - PDFOceanography
An Invitation to Marine Science
- Tom Garrison(Author)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. CHAPTER 12 338 Changes in sea level produce major differences in the posi-tion and nature of coastlines, especially in areas where the edge of the continent slopes gradually or where the coast is rising or sinking. Figure 12.3 shows an estimate of previous shore positions along the southern coast of the United States in the geologically recent past and a prediction for the distant future should the present warming trend cause more polar ice to melt. Because coasts are influenced by so many factors, perhaps the most useful scheme for classifying a coast is based on the pre-dominant events that occur there: erosion and deposition. Ero-sional coasts are new coasts in which the dominant processes are those that remove coastal material. Depositional coasts are steady or growing because of their rate of sediment accumulation or the action of living organisms (such as corals). The rocky shores of Maine are erosional because erosion exceeds deposition there; the sandy coastline from New Jersey to Florida is typically depositional because deposits of sediment tend to protect the shore from new erosion. The rocky central California coast is erosional, and the broad beaches of southern California are depositional. About 30% of the U.S. coastline is depositional, and 70% is erosional. We will use the erosional-depositional classification scheme in the rest of this chapter. C O N C E P T C H E C K Before going on to the next section, check your understanding of some of the important ideas presented so far: How is a shore different from a coast? What factors affect sea level and the location of a coast? How is an erosional coast different from a depositional coast? 12.2 Erosional Processes Dominate Some Coasts Land erosion and marine erosion both work to modify the na-ture of a rocky coast.
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.
eBook - PDF- James Petersen, Dorothy Sack, Robert Gabler, , James Petersen, James Petersen, Dorothy Sack, Robert Gabler(Authors)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
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. Once in the standing body of water, fine-grained sediments that stay in suspension for long periods may be carried out to deep water where they eventually settle out onto the basin floor. Other clasts are transported by waves and currents in the coastal zone, being deposited when energy decreases and, if accessible, reentrained 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 land- forms 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 mainland throughout its length (● Fig. 20.18). Many beaches are sandy, but beaches of other grain sizes are also common, as for for removal by wave erosion. Water is a key element in most weathering processes, and in addition to normal precipitation, rocks near the shoreline are subjected to spray from breaking waves, high humidities, and condensation. Salt weathering is particularly significant in preparing rocks for removal through chemical and physical weathering along the marine coast and coasts of salt lakes. Coasts of high relief are dominated by erosion (● Fig. 20.15). Sea cliffs (or lake cliffs) are carved where waves pound directly against steep land.
eBook - PDF- Tom Garrison, Robert Ellis(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
The rate of rise has slowed over the past 4,000 years and is now believed to be between 1.0 and 2.4 millimeters (0.04 to 0.1 inches) per year. a b Projections of global mean sea level rise through the year 2100. Because global sea-level projections face a lot of uncertainty, different scenarios are provided (represented here by colored lines). Even the most conser-vative of these predictions estimates a 20-centimeter (8-inch) rise. b Source: Global Sea Level Rise Scenarios for the United States National Climate Assessment, 2012 © Cengage Learning Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 CHAPTER 8 156 Figure 8.3 The southeastern coast of the United States, past and future. processes are those that remove coastal material. Depositional coasts are steady or growing because of their rate of sediment accumulation or the action of living organisms (such as corals). The rocky shores of Maine are erosional because erosion exceeds deposition there; the sandy coastline from New Jersey to Florida is typically depositional because deposits of sedi-ment tend to protect the shore from new erosion. The rocky central California coast is erosional, and the broad beaches of southern California are depositional. About 30% of the U.S. coastline is depositional, and 70% is erosional. We will use the erosional-depositional classification scheme in the rest of this chapter. 8.2 Erosional Processes Dominate Rocky Coasts Land erosion and marine erosion both work to modify the nature of a rocky coast. Erosional coasts are shaped and attacked from the land by any or all of the following: Stream erosion Abrasion of wind-driven grit Alternate freezing and thawing of water in rock cracks Plant root probing Glacial activity Rainfall Dissolution by acids from soil slumping (sinking or settling) From the sea, large storm surf routinely generates tremen-dous pressures on the coast.
No longer available |Learn more- James Petersen, Dorothy Sack, Robert Gabler(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
■ 20.5 Recount how sediment moves along a beach. ■ 20.6 Identify coastal erosion processes and the primary landforms found on erosion-dominated coastlines. ■ 20.7 Describe the types and sources of sediment found in coastal depositional landforms. ■ 20.8 Distinguish among the principal coastal depositional landforms. ■ 20.9 Summarize a global-scale and a regional-scale classification of coasts. ■ 20.10 Describe the different types of coral reef. OBJECTIVE WHEN YOU COMPLETE THIS CHAPTER YOU SHOULD BE ABLE TO: OUTLINE The Coastal Zone Origin and Nature of Waves Tides Tsunamis Geography’s Physical Science Perspective: Tsunami Forecasts and Warnings Wind Waves Breaking of Waves Coastal Geomorphic Processes Wave Refraction and Littoral Drifting Coastal Erosion Coastal Deposition Types of Coasts Geography’s Environmental Science Perspective: Beach Protection Islands and Coral Reefs Change over Time Map Interpretation: Active-Margin Coastlines Map Interpretation: Passive-Margin Coastlines COASTAL PROCESSES AND LANDFORMS 20 ▼ The shorelines of the world are extensive, complex, and often spectacular environments. David Crosbie/Alamy 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 572 warming significantly reduces the extent of the continental ice sheets, the ensuing rise in sea level will have a profound impact on the human-built infrastructure in coastal regions and on coastal geography and geomorphology.
eBook - PDF- Alan F. Arbogast(Author)
- 2017(Publication Date)
- Wiley(Publisher)
Beach drift Sediment that is transported in the surf zone by swash and backwash, which form due to the oblique approach of waves. Littoral drift Sediment that is transported through the combined processes of longshore drift and beach drift. 446 CHAPTER 19 Coastal Processes and Landforms Coastal Landforms Let’s now turn to the various landforms created along shore- lines. Recall that fluvial, glacial, and eolian landforms can be subdivided into erosional and depositional categories. Coastal landforms can be viewed in the same way. This discussion begins with erosional coastlines. Erosional Coastlines Most coastal erosion is accomplished through the unceasing pounding of the shoreline by waves. Waves have tremendous power after they break, with the associated spray moving as fast as 113 km/h (70 mi/h). Given that water has a very high density, the rapidly moving water has a lot of power and is responsible for the majority of coastal erosional landforms. Although wave erosion can occur along any part of the coast, it tends to be focused on a particular part of the land- scape called a headland. A headland is a promontory that juts into the ocean or sea and thus is surrounded on three sides by water (Figure 19.13). Headlands tend to form along shorelines where bands of rock with alternating resistance run perpendic- ular to the coast. The headlands are associated with the more resistant rock such as limestone or granite. Where the rock is relatively soft, perhaps shale or sandstone, waves can erode sediment more effectively and a bay forms. Once the pattern of headlands and intervening bays develops, the erosive power of waves begins to concentrate on the headlands. This change occurs because approaching waves initially begin to slow down in front of the headlands, Headland A portion of the coast that extends outward into a large body of water.
eBook - PDFPhysical Geology
The Science of Earth
- Charles Fletcher(Author)
- 2017(Publication Date)
- Wiley(Publisher)
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. Sediments on these coasts are coarse grained, and wet- lands and estuaries on them tend to be narrow and poorly developed. All these features are common to shorelines that generally act as sediment sources rather than as sites of sed- iment accumulation. Depositional coasts, in contrast, often are associated with old mountain systems that are no longer tectonically active. With long periods of geologic time during which to shed sediments into the coastal zone, a broad continental shelf to diffuse wave energy, and wide coastal plains to collect and store sediments, these coastal systems are characterized by abundant sediment that forms barrier island chains, deltas, broad lagoons, and extensive tidal wetlands. River valleys in them tend to be wide and flat. In general, depositional coasts are found in midplate settings where little active mountain building takes place (Figure 20.33). Test your understanding of these complex environments by completing the following Critical Thinking exercise. FIGURE 20.33 (a) Erosional coasts are characterized by eroding sea cliffs, sea stacks, and short beaches in narrow embayments. (b) Depositional coasts collect large quantities of sediment. Coastal wetlands tend to be found on depositional coasts. robertharding/Alamy Stock Photo (a) How is the tectonic setting likely to differ between erosional and depositional coasts? Concept Check 20.10 Please complete this exercise before coming to class. Identify the best answer to each question. 29. In time, the shoreline in this photo will: a. Develop deeper embayments. b. Grow larger headlands due to beach erosion. c. Not change significantly. d. Tend to straighten. e. None of the above. 30. Shorelines on tectonically stable lands that collect sediment are termed: a.
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 - PDF- James Petersen, Dorothy Sack, Robert Gabler, , James Petersen, Dorothy Sack, Robert Gabler(Authors)
- 2014(Publication Date)
- Cengage Learning EMEA(Publisher)
Amount and size of sediment supplied to the coastal zone vary with rock type, weathering rates, and other elements of the climatic, biological, and geomorphic environment. Sediment within coastal deposits comes from three prin-cipal 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 freshwater meet. Elsewhere, stream load may instead be delivered to the ocean or lake for continued transportation. Once in the standing body of water, fine-grained sediments that stay in suspension for long periods may be carried out to deep water, where they eventually settle out onto the basin floor. Other clasts are transported by waves and currents in the coastal zone, being deposited when energy decreases and, if accessible, reentrained when wave energy increases. The same is true of the second major source of Abrasion extends the notch landward, leaving the cliff above subject to rockfall and other forms of mass wasting. Stones that function as tools in abrasion quickly become rounded and accumulate at the base of the cliff as a cobble beach . Where the cliffs are well jointed but cohesive, wave erosion can create sea caves along the lines of weakness (Fig. 17.14b). Sea arches result where two caves meet from each side of a headland (Fig. 17.14c). When the top of an arch collapses or a sea cliff retreats and a resistant pillar is left standing, the remnant is called a sea stack . Landward recession of a sea cliff leaves behind a wave-cut bench of rock, an abrasion platform , which is sometimes vis-ible at lower water levels, such as at low tide (Fig. 17.14d). Abrasion platforms record the amount of cliff recession. In some cases, deposits accumulate as wave-built terraces just sea-ward of an abrasion platform.
No longer available |Learn more- Donald Hyndman, David Hyndman(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
Beaches and Sand Supply Beaches are accumulations of sand or gravel supplied by sea-cliff erosion and river transport of sediments to the coast. The size and number of particles provided by sea-cliff ero- sion depend on the energy of wave attack, the resistance to erosion of the material making up the cliff, and the particle size into which the cliff material breaks. Waves often under- cut a cliff that collapses into the surf (FIGURE 15-7) and then break it into smaller particles. The size and amount of mate- rial supplied by rivers depends similarly on the rate of river flow and the particle size supplied to its channel. Thomas Garrison Donald Hyndman 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. Waves, Beaches, and Coastal Erosion 415 As waves travel into shallow water and begin to touch bot- tom, they shift sediment on the bottom, stirring it into motion and moving it toward the shore. Most sediment moves at water depths of less than 10 m. Long-wavelength storm waves, however, with periods of up to 20 seconds, reach deeper; they touch bottom and move sediments at depths as great as 300 m on the continental shelf. Those large waves have the energy to spread the grains into a gentler slope; they erode the grains above water level and deposit them off- shore below sea level. FIGURE 15-7 Waves Undercut a Cliff This cliff on Kauai, Hawaii, has been undercut by waves. Large chunks of rock break off and are pounded into sand by the waves.
eBook - PDF- David Huddart, Tim A. Stott(Authors)
- 2019(Publication Date)
- Wiley-Blackwell(Publisher)
However, despite these generalizations, time‐aver- aged, and space‐averaged rates of erosion are extremely variable and can be measured by a range of techniques, such as comparing old photos and aerial photos, direct measurements of the exposure of steel pegs or nails driven into the cliff, and micro‐ erosion metres. 19.5.1.7 Beaches To many people, the word ‘beach’ conjures up pic- tures of the Sun, tanned bodies and crashing waves, but beaches occur in most climates and are not always blessed by sunshine. A more precise defini- tion is: a wave‐deposited, three‐dimensional body of cohesionless and unconsolidated sediment (sand or gravel) along a coast extending above the lowest water mark (spring low tide), or a line of breakers at low tide to cliff or dune. It is the upper part of the shoreface and has a concave‐upwards profile. The key to this definition is the word ‘cohesionless’, which implies that the sediment is free to move and be re‐ shaped by the incident waves if the current velocities generated by them exceed the transport thresholds of the grain sizes present on the beach. Beaches can be composed of a range of particle sizes, from fine sand to cobble, or even boulder gravel, and all beaches have one thing in common: an ability to dissipate wave energy. This can be viewed conceptually in terms of the availability of excess energy for sediment transport. Sediment is moved on a beach by waves and the currents they generate so as to reduce the excess energy present. If excess energy is high, perhaps during a storm event, sedi- ment is transported offshore and the beach profile flattened, which increases the effective energy dissi- pation on the beach and therefore the excess energy present. In this way, a beach’s morphology is brought in line with the prevailing energy conditions.
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