WIND, WAVES AND CURRENT

1. WIND, WAVES AND CURRENT and their effects

2. WIND • Winds pick up and move sediment • Winds drive sediment against rock and other materials, causing weathering • Wind erosion is most effective in areas of loose sand, silts and clay • Common in deserts, beaches and semi-arid regions

3. Abrasion • Sand grains are larger (than silts and clay) and tend to be more abrasive • Desert sands blast and grind boulders and rocks into ventifacts (side of rock that faces wind wears into a smooth, flat surface or facet)

4. Deflation • Deflation is the removal of loose rock particles by the wind • When the surface particles are removed (sands, clays), pebbles and rocks are left behind, called desert pavement.

5. SAND DUNES • Sand dunes are hills of sand deposited by winds and are formed when the sand piles up against shrubs, boulders and other obstructions • They occur where there are strong winds and enough loose sand (deserts, sandy flood plains and beaches) • Dune sands are usually made of quartz, but sometimes gypsum, calcite or others.

6. Dune Shapes/Types

7. Dune Shapes/Types BARCHAN: cresent shaped dunes, where the ends point downwind. TRANSVERSE: long continuous sand ridges, that form at right angles to the wind PARABOLIC: u-shaped dunes (like barchans) but their ends face upwind LONGITUDINAL: long and straight dunes that are parallel to the wind direction

8. Dune Migration • Each time the wind blows against the windward side of a sand dune, sand is blown over the top, and falls down onto the leeward side (called the slip face) • As a result the dune moves!

9. WAVES Waves can be produced in one of three ways: • Wind • Undersea earthquakes • Effects of the moon (tides) Waves begin as ripples and as they grow larger they become waves. The height of a wave depends on: • The length of time the wind blows • The fetch or length of open water over which the wind blows.

10. Anatomy of a Wave • Wave height is the difference between its crest and trough. • Wavelength is the distance from one crest to the next (strong winds make waves with long wavelengths) • The period of a wave is the time it takes one wavelength to pass a given point SPEED=WAVELENGTH PERIOD

12. Wave Motion • Water is not carried along with the motion of a wave….each water molecule moves in place in a circular motion….and bumps into the next molecule which passes along the energy • Water molecules move in smaller and smaller circles as depth increases. • Waves bend (refract) when they approach a shoreline

13. Breakers • As the wave scrapes the bottom, the circular motion of the wave is distorted (lower part slows down, upper part moves ahead) • The crest falls over and breaks into surf that washes onto the beach • The surf is a powerful agent of erosion.

14. Shoreline Currents • Waves can come from any direction and thus strike shorelines at angles • When waves break, large amounts of water and sand are pushed up the beach (swash) • Most of the water runs back down the beach under the next wave in a gentle current called backwash (strong backwash is called an undertow!)

15. Longshore and Rip Currents • Water past the breakers is also pushed towards the shore by waves and pulled back by backwash, and the movement forms a longshore current, which runs parallel to the shore. • Rip currents are strong surface currents that flow away from the beach, which can pose a serious problem for swimmers.

18. Erosion of Shorelines • Breakers easily remove large masses of sand and clay • Bedrock is scoured away by sand and pebbles • Seawater dissolved minerals from rocks such as limestone • Sea cliffs, sea caves, sea arches and stacks may form

20. SANDBARS • Many times a longshore current carries enough sand to form a sandbar across the mouth of a bay. • A spit is a sandbar attached at one end • A baymouth bar is one that has grown completely across the bay • A spit with a curved end is called a hook • Sandbars protect the water behind them from wind and waves (form lagoons)

21. Spits & Hooks

22. Baymouth Bars

23. Barrier Islands • Sandbars not attached to the shoreline • Run parallel to it

24. Beaches and Shorelines • A beach is the area between high-tide level and low-tide level • Beaches can be sandy, pebbly or rocky • If the seafloor slopes gently, only clay washes out (by backwash) and sand remains. • If the seafloor is steep, sands and clay are washed out to sea and pebbles remain.

25. Other Shoreline Features • Fiords are long, deep-sided bays formed when glacial troughs were flooded. • Irregular shorelines zig zag • Regular shorelines are fairly straight

26. Corals and Reefs • Corals are tiny sea animals that live in colonies, which have shells made of calcium carbonate • When they die, their shells are left behind and new corals grow on top • Large buildups of coral shells are called coral reefs

28. Fringing and Barrier Reefs • Coral colonies growing close together form fringing reefs • A fringing reef slowly moves ocean ward, because the coral grows on the ocean side where ocean waves bring food • A barrier reef forms when a fringing reef moves away from shore

29. The Great Barrier Reef-Australia