Water and Weather

2. Water and Weather

3. Chapter Seven: Oceans • 7.1 Introduction to Oceans • 7.2 Waves • 7.3 Shallow Marine Environments • 7.4 The Ocean Floor

4. 7.3 Shallow marine environment • A beachis an area of coastal sand between the low tide line and the line of permanent vegetation. • The backshoreis the part of the beach above the high tide line which is only submerged during storms. • The foreshoreof a beach lies between the high and low tide lines.

5. 7.3 Shallow marine environments • Sea level is the average ocean height between the high and low tide levels.

7. 7.3 Sandy beaches and tidal flats • Sand is the most obvious feature of a beach. • The light-colored, rounded grains slip easily through your hands.

8. 7.3 Sandy beaches and tidal flats • Tidal flats commonly have sandy areas, but most of a tidal flat is dark, sticky mud.

9. 7.3 Sandy beaches and tidal flats • Tidal flats and beaches are both covered by sediment. • Streams and rivers carry the sediment down from the mountains and other high places.

10. 7.3 Sandy beaches and tidal flats • Waves are the key difference between tidal flats and beaches. • Beaches are affected by strong wave action. • Tidal flats are not. • Waves change the size of sediment particles. Scientists use special cameras to measure particles and wave action.

11. 7.3 Waves and sand • The largest particles of sediment are heavy enough to settle to the ocean floor. • The smallest particles and broken grains are carried out to sea with the waves and ocean currents.

12. 7.3 Beaches in winter and summer • Gentle summer waves carry sand from deeper water onto the beaches. • The stronger winter waves carry the sand back to deeper water.

13. 7.3 Moving sand • Beaches never completely wear away because rivers and streams bring new sand from the mountains to the beaches. • This sand doesn’t stay in one location. • In some places the shore resists wearing away.

14. 7.3 Moving sand • A coastis the boundary between land and a body of water like the ocean. • This movement of sand along a coast is called longshore drift.

15. 7.3 How does longshore drift work? • Longshore drift occurs because waves approach the beach at an angle.

16. 7.3 How does longshore drift work? • The waves come in at one direction (the upwash) and then leave the beach at a different angle (the backwash).

17. 7.3 Barriers and breakwaters • A breakwater is a barrier to longshore drift that protects harbors. • Excess sand builds up near a breakwater and must be removed regularly.

18. 7.3 The continental shelf • Sand drifting down the steep face of a continental shelf cuts into the shelf just like streams cut into valleys.