Download The Ocean Shoreline - Milan Area Schools

The Ocean Shoreline
(or Why does the beach look the
way it does?)
Shoreline = where land meets the
ocean (or Great Lake!)
But why are shorelines so different?
Shoreline Forces
Shorelines are shaped by three main
forces:
1. Waves – wind blowing across the
water creates waves
- However, waves do not move water
- They move energy
- That energy erodes & moves a lot of
shoreline (especially what kind of
rocks?)
Wave energy moves the water up and
down. The wave is just as tall on top as
it extends below the water. So when
they get close to shore, they “drag” on
the bottom and can move sand upshore.
Shoreline Forces cont....
2. Currents – Currents are masses of
moving water
- Waves usually collide with the shore
at an angle
- This creates a longshore current
that runs parallel to the shore
- The longshore current carry tons of
sediment and act as rivers of sand in
the ocean
The longshore
current forms
when the
waves come in
to shore and
get deflected
parallel
Shoreline Forces cont....
3. Tides – Tides are the rising and
falling of the level of the ocean caused
by gravitational pull of the moon and sun
FYI – Tides don't really move. The
Earth rotates under the water bulge
caused by the gravitational attractions.
- They do create tidal currents parallel
to shore that move sediment
Most tides only change 1m (~ 3 feet) per day but
the Bay of Fundy goes nuts. This is high tide.
This is the Bay of Fundy at low tide. Its
tidal difference can get to 15 m (~45 feet)
Tide Types
High and Low Tides:
- Usually happen once a day and
sometimes twice a day in some places
Spring and Neap Tides:
- Spring tides are higher than normal high
tides caused by the moon & sun being in line
& pulling together (the low tides are even
lower then too)
- Neap tides are lower than normal high and
low tides caused by the moon & sun pulling
against each other
Spring
Neap
Moon and Sun Positions during Spring
and Neap tides
Rocky Shorelines
Rocky shorelines are formed by waves
and currents constantly pounding the
shoreline.
The reason why these areas are rocky
instead of sandy is because the cliffs
are formed from much harder rocks
than the parts that are eroded away.
(Remember Moh's Scale?)
These areas eroded away because they were
formed from softer rocks leaving the jagged
cliffs you see here.
Sandy Beaches
Not all sand is created equal....
Sandy Beaches form when waves break
down rock from the shoreline or transport
sand from somewhere else.
Sand grains can range in size from 0.06 mm
to 2 mm in diameter.
Sand particles can be different colors
depending on the minerals it is formed from.
Sand Colors
* Black sand forms
from volcanic basalt.
* Green sand forms
from the mineral
olivine
* Pink sand forms
from coral
* White Sand forms
from quartz, coral &
shell fragments
Sand Erosion
Beaches erode easily since sand particles are
small and loosely bonded.
Storms, currents and winds can move sand.
Often along coasts, sand will build up
offshore and eventually form barrier
islands that can exist for a few years to a
few centuries (so probably not the best palce
to build a vaction home!)
Barrier Islands off the coast of South
Carolina