The Work of Waves and Wind The Work of Waves Beaches Types of Coastlines Wind Action Sand Dunes Loess

The Work of Waves  Crests and troughs (high and low points)  Wave height is the vertical distance between trough and crest ( called amplitude)  Wave length is the horizontal distance from trough to trough, or from crest to crest  The wave period is the time in seconds between successive crests or successive troughs that pass a fixed point

The Work of Waves  Wave height is related to wind speed, duration, and fetch ( the uninterrupted distance over the sea for which the wind blows without a change in direction)  High winds over long distances and long durations can create very large waves  As waves approach the shore, wave length decreases and height increases until the wave becomes unstable and breaks

Waves  The energy of the breakers (crashing waves) causes erosion and transportation of shoreline materials.  Wave action is the most important agent in shaping shoreline landforms

Tidal Currents Tides rise (FLOOD) to produce a HIGH TIDE and fall (EBB) (LOW TIDE) because of the gravitational pull that the Sun and Moon exert on the earth’s surface (including the oceans)

The top image was taken at 11:32am and the bottom photo was captured at 5:24pm on the same day The Bay of Fundy is located on the Atlantic coast of North America, on the northeast end of the Gulf of Maine between the Canadian provinces of New Brunswick and Nova Scotia.

The Work of Waves Waves erode weak materials rapidly to make beach scarps called sea cliffs and resistant materials over a long period of time to make marine cliffs called headlands.

The Work of Waves Sea cliff: the wave-cut notch, marks the line of most intense wave erosion

The waves find points of weakness in the bedrock and penetrate deeply to form crevices, sea arches, sea stacks and sea caves

The Work of Waves  Where a more resistant rock mass projects seaward, it may be cut through to form a sea arch  After an arch collapses, a rock column, known as a stack, (eventually, the stack is toppled by wave action and is leveled)

Terraces As the sea cliff is worn, a nearly level platform called a wave-cut terrace, usually remains beneath the water at the base of the cliff. The eroded material may be deposited offshore to create an extension to the wave-cut terrace called a wave-built terrace.

The Work of Waves and Wind The Work of Waves Beaches Types of Coastlines Wind Action Sand Dunes Loess

Beaches  Beaches are thick wedge shaped accumulations of sand shaped by the swash and backwash of water along the shoreline  Breakers attacking the shore at an angle produce littoral drift, - a movement of sediment along the shoreline – as well as longshore drift - a sediment movement just offshore

Beaches  Longshore current operates to shape shorelines - where a bay exists, the sand is carried out into open water as a long finger, or sandspit  As the sandspit grows, it forms a barrier, called a bar, across the mouth of the bay Figure 18.7, p m/watch?v=t7J81cQr6eIwww.youtube.co m/watch?v=t7J81cQr6eI

San Diego’s Sandspit

Beaches  When sand arrives at a particular section of the beach more rapidly than it is carried away, the beach is widened and built oceanward - this change is called progradation (building out)  When sand leaves a section of beach more rapidly than it is brought in, the beach is narrowed and the shoreline moves landward - this change is called retrogradation (cutting back )

The Work of Waves and Wind The Work of Waves Beaches Types of Coastlines Wind Action Sand Dunes Loess

Types of Coastlines Two groups: One group of coastline types derives its qualities from submergence, the partial drowning of a coast by a rise of sea level or a sinking of the crust. Another group derives its qualities from emergence, the exposure of submarine landforms by a falling of sea level or a rising of the crust.

Types of Coastlines Figure 18.14, p. 608

Submergent Coastlines  Ria coastlines: flooded river valleys  Fiords: is a long, narrow inlet with steep sides or cliffs, created in a valley carved by glacial activity.inletglacial activity  Estuary:mouth of river valley submerged by ocean water and form a wide, shallow bay

Types of Emergent Coastlines Coastlines created when new land is built out into the ocean:  Deltas  Volcano coasts  Coral Reef Coasts  Barrier Islands

Types of Coastlines A delta coast results when a river empties into the ocean Figure 18.18, p. 610

Types of Coastlines coral reef coasts occur in warm oceans where corals build reefs at the land-sea margin (fringing reefs, barrier reefs and atolls) volcano coasts are found where fresh volcanic deposits of lava and ash reach the ocean

The Work of Waves and Wind The Work of Waves Beaches Types of Coastlines Wind Action Sand Dunes Loess

Wind Action Wind is selective: only the finest particles (clay and silt) are lifted and raised into the air sand grains are moved only when winds are at least moderately strong and usually travel within a meter or two of the ground (saltation: movement by short jumps or bouncing) Figure 18.24, p. 615

Effects of Wind Erosion While wind erosion happens almost everywhere there is wind, the landscapes that are most affected by wind erosion are deserts and coastlines. One common form of wind erosion is deflation( process by which wind removes the top layer of fine, very dry soil and rock particles and leaves behind large rock particles. These particles often form a surface of closely packed small rocks called desert pavement.

Deflation cont. Deflation may form shallow depressions in areas where the natural ground cover has been removed. As the wind strips off the topsoil, a shallow depression called a deflation hollow forms. Ventifacts are also formed by the wind’s erosive force. The direction of prevailing wind in an area can be determined by the appearance of ventifacts.

Wind Action Wind performs two kinds of erosional work: Abrasion- wind drives sand and particles against an exposed rock or soil surface - causes the surface to be worn away by the impact of the particles Deflation- the removal of loose particles from the ground, acts on loose soil or sediment

Wind Deposition The wind drops particles when it slows down and can no longer carry the material. Over long periods of time cementation and pressure from overlying layers bind the fragments together. This is one way in which sedimentary rocks are formed. The best known wind deposits are called dunes, which are mounds of wind-deposited sand.

wind direction BACKSLOPE SLIPFACE movement of sand angle of repose crest Sand Dunes

Barchan dune is a crescent shaped heap of sand that moves across a flat, pebble-covered plain - the points of the crescent are directed downwind Types of Sand Dunes Figure 18.25, p. 615

Parabolic dunes are bowed outward in the downwind direction – the opposite of barchan dunes Sand Dunes Figure 18.27, p. 618

Longitudinal dunes run parallel to the direction of the wind Sand Dunes Figure 18.28, p. 619

Sand Dunes : continued Transverse dune: forms at right angles to the wind direction

LOESS A Loess is a deposit of wind-blown silt that may be as thick as 30 m in some regions of North America It forms highly productive but easily eroded soils Figure 18.30, p. 620