To develop understanding of processes and landforms, students could watch the clip without the commentary and try to write one as they watch. They could then read out their comments and try to justify their ideas. They could then watch again with the sound and compare their ideas with the real commentary. Finally, they could develop a labelled sequence of diagrams of the formation of a spit from the clips and their commentary.
Description Classroom Ideas. Very strong winds are therefore required to generate the biggest waves. Figure 2 The highest waves occur in the Southern Ocean and north Pacific and Atlantic where they are generated by strong sub-polar lows. While the sub-tropical trade winds also blow year round across huge sections of ocean, they are of only moderate velocity, and hence generate only moderate waves.
All rights reserved. When waves are being generated they are called a sea and consist of short, steep, high, slower waves, which tend to topple over and break, and have a broad spectrum of direction. Swell waves can theoretically travel around the world with minimal loss of energy, while in reality they eventually break on some distant shore.
Tides are produced by the gravitational pull of the Moon and Sun acting on a rotating Earth. This pull produces a very slight bulge in the ocean, which we know as tide. The major impact of tides is to shift the shoreline between high and low tide, and to generate tidal currents either parallel to the coast, or at tidal inlets and estuaries, currents flowing into the inlets and perpendicular to the coast Figure 3.
Figure 3 Tidal inlet at Merrimbula, Australia. Tidal currents ebb and flood though the narrow inlet moving marine sand from the beach into the inlet to form a deep tidal channel and shallow sandy tidal delta.
Fluvial systems deliver sediment to the coast where it is deposited in estuaries and deltas. Depending on their location, deltas are also acted on by waves, tides, and other currents, and shaped to suit the prevailing processes. Sediment can also be moved longshore to supply beach and barrier systems Figure 4.
Figure 4 The Gasgoyne River delta in Western Australia delivers large volumes of sand to the coast where it is deposited in river mouth shoals and slowly reworked longshore to supply downdrift spits, barriers, and dunes.
Beaches are wave-deposited accumulations of sediment located at the shoreline. They require a base to reside on, usually the bedrock geology, waves to shape them, sediment to form them, and most are also affected by tides. The beach extends from wave base where waves begin to feel bottom and shoal, across the nearshore zone, though the surf zone to the upper limit of wave swash Figure 5.
In the coastal zone ocean waves are transformed by shoaling, breaking, and swash. In doing so they interact with the seabed, and determine the beach morphology or shape, a process called beach morphodynamics.
Figure 5 An idealised cross-section of a wave-dominated beach system consisting of the swash zone which contains the subaerial or 'dry' beach runnel, berm, and beach face and is dominated by swash processes; the energetic surf zone bars and channels with its breaking waves and surf zone currents; and the nearshore zone extending out to wave base where waves shoal building a concave upward slope.
All beaches consist of sediment , which can range in size from sand up to cobbles and boulders. In the mid latitudes most beaches are composed of siliceous or quartz sand grains derived from erosion. In the topics, coral reef detritus and shells known as 'carbonate sediment' tend to dominate, Figures 6c and 6d , while in higher latitudes physical weathering produces coarse rock fragments and gravel. Sediments may therefore be derived from the land and delivered via rivers, glaciers and shoreline erosion, and from marine organisms in the sea.
Once at the shore they are moved onshore by wave, tide, and wind driven currents to form beaches. A positive sediment supply produces beach accretion while when negative beaches erode Figure 7. Figure 7 a Greenmount Beach in Queensland, Australia widened by m as a result of beach nourishment.
At the beach the three zones of wave transformation shoaling, breaking, and swash produce three morphologically distinct sub-systems Figure 5. As they shoal they interact with the seabed, slowing down and increasing in steepness and height Figure 8. Figure 8 View of Makapu Beach, Hawaii, showing waves shoaling and steepening as they travel across and interact with the nearshore zone, then breaking across the surf zone.
The surf zone is the most dynamic part of the beach and extends from the breaker zone to the shore. Waves break when the water depth is approximately 1. They can break as a spilling breaker on low gradient slopes, a plunging wave on moderate gradients, or a surging wave on steep slopes. In breaking, waves transform their potential energy to kinetic energy, which is initially manifest as the broken wave of translation, or wave bore , which moves shoreward as broken white water.
At the shoreline the currents can be deflected longshore and water may return seaward as a rip current. Surf zone currents can transport sediment onshore, longshore and offshore and build the sand bars and troughs that occupy the surf zone Figure 5. The number and location of the bars is a product of infragravity waves , a low frequency greater 30 sec period wave produced by sets of higher and lower waves and which is enhanced by wave breaking across the surf zone.
The longer the infragravity wave period the more widely spaced the bar s. Another form of infragravity wave called edge waves also influence the longshore spacing of rip currents and channels, which are typically — m apart on ocean beaches.
Rip currents are narrow, seaward moving currents that move seaward though the surf zone, often in a deeper rip channel Figure 9a. They are a mechanism for returning the water back out to sea, and a conduit to transport seaward eroded beach sediment Figure 9b during high seas. They are also a major hazard to beach goers and responsible for most beach rescues and drowning Short Figure 9 a Low waves breaking on a shallow bar and flowing shoreward into a rip feeder channel.
The dye highlights the rip feeder current flowing along the base of the beach face, then turning to flow seaward in the deeper rip channel. When the broken wave reaches the base of the wet beach it collapses and runs up the beach face as swash or uprush in the swash zone Figure The uprush stops toward the top of the slope, some percolates into the beach, the remainder flows back down the beach as backwash.
As sediment is deposited in the swash zone it can build a berm , a near horizontal to slightly landward-dipping sand surface, the area where most people sit when they go to the beach. The swash zone may also contain beach cusps , spaced about every 20 to 30 m and produced by another form of edge wave Figure Figure 10 Wave runup on the steep beach face at Ke lli Beach, Hawaii.
Figure 11 A steep reflective beach with well developed high tide beach cusps at Hammer Head, Western Australia. Wave-dominated beaches have an RTR tide range less than three times the average wave height RTR Reflective beaches are produced by lower waves H Figure 12 A plot of breaker wave height versus sand size, together with wave period, that can be used to determine the approximate beach state for wave-dominated beaches.
To use the chart, determine the breaker wave height, period and grain size mm. They are characterized by a surf zone with one or two bars up to m wide. The bar is usually cut by regular rip channels and currents Figure Figure 13 Well-developed intermediate beach containing transverse bars and rip channels along Lighthouse Beach, Australia.
Note the waves breaking on the bars, with no waves breaking in the deeper darker rip channels. Also note the rhythmic shoreline protruding in lee of the bars and forming an embayment in lee of the rips.
Waves break on the outer then inner bar s , thereby dissipating their energy as the move across the surf zone Figure The swell breaks over the wide outer bar, reforms in the central trough, then breaks across the inner bar, resulting up to 10 lines of breakers and a m wide dissipative beach and surf zone.
They usually have a steep, coarser-grained, cusped, reflective, high tide beach. This is fronted by a wide, finer-grained, low gradient, often featureless, intertidal zone, up to m wide, then a low tide surf zone which may contain bars and rip channels Figure Figure 15 A steep reflective high tide beach face fronted by a m wide tide-modified low tide terrace crossed by shallow drainage channels at North Harbour Beach, Australia.
An additional beach type consists of a high tide reflective beach face fronted by intertidal rocks flats, and in the tropics a high tide beach fronted by a fringing coral reef flat Figure Furthermore any beach located in the high latitudes will be seasonally exposed to freezing air and water temperatures leading to the development of sea ice, shoreface ice, and a frozen snow covered beach Figure Figure 18 The beach at Pingok Island, north Alaska, shown a during summer, with floating ice against the shore; b during freeze-up, with snow and sea ice accumulating; and c the frozen winter beach and ocean.
Beach systems are an essential component of a larger scale coastal landform called barriers , which are long-term accumulation of wave, tide, and wind deposited marine sediment usually sand at the shore. When separated from the mainland by lagoons and marshes Figure 19 they are called barrier islands Figure 20 , which occur along the US East and Gulf coasts. Some are backed by large dune systems as along the Oregon coast. Figure 19 A coastal sand barrier consisting of a beach and vegetated dunes, backed by a lagoon, at Big Beach, Queensland, Australia.
Figure 20 A series of low barrier islands separated by tidal inlets, at Corner Inlet, Victoria, Australia. Davis, R. Groynes add sediment to the beach by capturing downward drift. Longshore Drift littoral drift Longshore drift is a process responsible for moving significant amounts of sediment along the coast. The swash moves beach material along the beach and the backwash, under gravity, pulls the material back down the beach at right angles to the coastline. What does longshore drift do to the beach?
Category: travel beach travel. The transport of sand and pebbles along the coast is called longshore drift. The prevailing wind the direction the wind ususally blows from causes waves to approach the coast at an angle. What problems can longshore drift cause? Why do waves approach a beach at an angle? What stops longshore drift? What is beach drift? What can longshore drift create? Is longshore drift erosion? What is the source of sand on beaches?
Do waves approach the shore at an angle? How is beach sediment size measured? How do you identify longshore drift? What is beach gradient? What is beach profile? Why do a beach profile? Beach profiles. What are fieldwork techniques? What is Updrift and Downdrift?
Do groynes prevent longshore drift? How is longshore drift managed? Longshore Drift littoral drift.
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