Water and Weather

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

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

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

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.

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

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.

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.

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.

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.

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.

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

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

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).

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.

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.