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.