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The Story Behind Them By: Mr. Liu

The Story Behind Them By: Mr. Liu. Waves.

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The Story Behind Them By: Mr. Liu

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  1. The Story Behind Them By: Mr. Liu

  2. Waves • Waves begin on the open sea. Their height depends on how fast, how long, and how far the wind blows over the water. An increase in any of these variables can cause an increase in wave height. Hurricane winds can create waves 30 m high. On a calm day, there is usually a steady movement of smooth waves near the shore. These smooth waves are called swells. They are caused by winds and storms far out at sea. • A wave’s height is measured from its crest (the highest part of the waves) to its trough (the lowest part of the wave). Second, waves a also have a wavelength, which is the distance from one crest to the next. Third, waves have a speed of motion, which is measured by the time required for one wave to pass a given point.

  3. Waves • Wave motion: The wave form is what moves. Each individual water molecule simply moves in a circle as the wave form passes. The circles become smaller with increasing depth.

  4. Waves • When a wave reaches shore, it changes shape. As the trough of the wave touches the beach, it is slowed down by friction. The crest of the wave, however, continues moving at the same speed. The wavelength shortens, and the wave height increases. The crest of the wave eventually out runs the trough and topples forward. The wave collapses onshore in a tumble of water called a breaker.

  5. Waves Questions • 1. How does a breaker form? (2 marks) • 2. Name three factors that determine the height of a wave. (3 marks)

  6. How Waves Change Shorelines • The energy in waves shapes and reshapes coastlines around the world. Along some coastlines, churning waters swirl rocks and pebbles on narrow strips of land between steep sea cliffs and the ocean. On other coastlines, gentle waves lap broad, gently-sloping beaches of find sand.

  7. How Waves Change Shorelines • Some coastlines have a zigzag shape that forms a series of bays (parts of the ocean that reach into the land) and headlands (areas of land that stick out into the sea). Waves approaching shore strike headlands first. They slam into the rocks with a force of up to thousands of kilograms per square metre. This impact breaks off chunks of rock from the headland, producing vertical sea cliffs that extend into deep water. After hitting headlands, waves lose much of their energy. They slow down and spread out into nearby bays and coves. In these places, the water arrives on shore with much less force compared with the water striking headlands.

  8. How Waves Change Shorelines • At the base of a sea cliff, masses of loose rock and pebbles swirl around in breaking waves. Softer rock near the base of a cliff is removed by this action and then washed away. Over time, this process of erosion may hollow out the rock to form sea caves and arches in the cliff. Seawater can dissolve certain minerals in rock, increasing erosion by chemical action. The combination of all these processes can erode areas of rocky shoreline by as much as 1 metres in a year.

  9. How Beaches Are Formed • As fragments of rock nibbled from the coast of crashing waves rub against each other, rock fragments are smoothed and ground down into smaller pebbles and grains of sand. Along steeply-sloping shorelines, these rock fragments wash back into the sea. This leaves a shoreline of only bare rock; with scattered boulders and larger stones. Where the shoreline has a gentler slope and calmer waves, smaller rock fragments can settle and build up, forming a broad beach.

  10. How Beaches are Formed • Beaches are deposits of sediment that run along the shoreline. The materials that form a beach range in size from fine grains of sand less than 2 mm in diameter to pebbles and small boulders. Most beach sediments are fragments of hard minerals such as quartz. Beaches can also include other minerals of various colours, or fragments of seashells and coral. • Due to the continuous action of waves, beaches are in constant state of change. In winter, strong winds bring larger waves that remove more sediment from the beach than they deposit. The beach erodes and becomes narrower. Winter waves may damage boardwalks and beachside dwellings. Calmer summer weather produces low, gentle waves that deposit sediments on shore, rebuilding the beach.

  11. How Waves Change Shorelines Questions • What processes produce bays and headlands? (5 marks) • How is a sandy beach formed? (5 marks)

  12. Convection Currents Cooler water, air, and magma are attracted to heat sources. Once, they reach the heat source, they circulate towards cooler areas.

  13. Ocean Currents Ocean currents circulate from both the North and South Poles towards the equator which is the warmest part on the earth’s surface. Once the ocean currents reach the equator, they retreat back towards their respective poles.

  14. Ocean Currents • The rotation of the Earth produces a deflection (bending of moving currents called the Coriolis effect. As wind and water currents flow over Earth’s surface, the planet turns beneath them from west to east. This motion causes currents in the northern hemisphere to turn to their right relative to the Earth’s surface. In the southern hemisphere, the effect causes currents to turn to their left. The overall result of the Coriolis effect is that winds along the equator blow from the east. These winds, called trade winds, push ocean currents toward the west. Toward the polar regions, westerly winds drive currents the opposite way, from west to east.

  15. Tides • Beaches are sometimes covered by water, and sometimes they are not. They are covered and uncovered in a regular daily cycle by the slow rise and fall of the ocean, called tides. Centuries ago, people realized that the cycle of tidal movement is linked to the motion of the Moon. The largest tidal movements (spring tides) occur when Earth, Moon, and Sun are in a line. At these times, tides are extra high and extra low. The smallest tidal movements (neap tides) occur when the Sun and Moon are at right angles to each other. On these days, there is little difference in depth between high and low tides. The difference in level between a high tide and a low tide is called the tidal range.

  16. Tides • The link between Earth, the Moon, the Sun, and tides is gravity. Gravity is the force of attraction between two masses. Tidal movements result mainly from the pull of the Moon’s gravity on the ocean. The Sun is much farther from Earth than the Moon is. Thus, the Sun has less than half as much influence on the tides as the Moon does, despite the Sun’s much greater size.

  17. Tides Questions • 1. Explain the difference between spring tides and neap tides. (4 marks) • 2. Explain why the Bay of Fundy has a large tidal range. (2 marks) • 3. What is the Coriolis effect? Explain in your own words. (4 marks)

  18. References: • http://www.lcsd.gov.hk/CE/Museum/Space/EducationResource/Universe/framed_e/lecture/ch06/imgs/tides.jpg, October 15, 2009 • http://www.uwgb.edu/DutchS/Graphics-Geol/Oceans/OceanCurrents.gif, October 15, 2009 • http://www.uwgb.edu/DutchS/EnvirGeolNotes/HowEarthWorks.HTM, October 15, 2009 • http://www.maineislandkayak.com/images/OS_library/tides_current_hdr.jpg, October 15, 2009 • http://www.geography.learnontheinternet.co.uk/images/coast/waves.gif, October 15, 2009 • http://www.crd.bc.ca/watersheds/protection/geology-processes/images/clip_image002temp_003.jpg, October 16, 2009 • http://news.caloosahatchee.org/docs/mangrove_4.jpg, October 16, 2009 • http://www.geol.umd.edu/~jmerck/geol100/lectures/30.html, October 16, 2009 • http://www.kidsgeo.com/geography-for-kids/0089-coriolis-effect.php, October 16, 2009 • http://www.outback-australia-travel-secrets.com/image-files/australia-beaches-3.jpg, October 16, 2009 • http://www.destination360.com/caribbean/dominican-republic/punta-cana/images/s/punta-cana-beaches.jpg, October 16, 2009 • SciencePower 8, Science, Technology, Society, Environment, McGraw-Hill Ryerson Limited, 1999

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