Chapter 16
The Marine Environment
Longshore currents
• Waves usually
•
approach the beach
at an angle
Water recedes
parallel to the beach.
Longshore currents
• This repetitive wave
•
•
•
motion creates a flow of
water in one direction
along the shore.
The waves do deflect
depending on the shape
of the coast.
The larger the waves the
strong the current.
Waves produce erosional
and depositional
landforms on beaches.
Groins will catch sand carried by the
Longshore current.
Which way is the Longshore
current flowing in this picture?
Jetties and Seawalls
Erosional landforms
• Water crashing on the
•
beach as surf will
erode material away even solid rock.
Headlands receive
most of the wave
force because of
wave refraction.
Erosional landforms
•
•
•
•
Sea stacks
Wave cut platform
Wave cut cliff
Sea caves
Beaches
• Beaches can be mud,
•
sand, pebbles,
cobbles, gravel, or
rocky.
Color of the sand
depends on material
eroded.
Beaches
• Hawaii has black
•
sand beaches in
some locations.
The eroded material
is dark volcanic rock.
Beaches
• Florida and the
Bahamas white and
pink sand beaches
are bits of local coral
and sea shells.
Estuaries
• Occur where a river
•
•
•
meets the sea.
Formed by rising sea
level flooding a river
valley.
Water is brackish
These areas provide an
excellent environment for
wildlife. (protection, quiet
water, food)
Depositional landforms
• Spit
• Which way is the
current flowing?
Depositional landforms
• Tombolo
Depositional landforms
• Baymouth bar
Depositional landforms
• Lagoon
• Bay
Depositional landforms
• Barrier Island
*** Coastal landforms
•
•
•
•
•
•
•
•
Depositional
Beach
Spit, Baymouth bar
Tombolo
Bay or Lagoon
Barrier Island
Longshore bar
Sand bar
•
•
•
•
•
•
•
Erosional
Beach
Sea stack
Wave cut platform
Wave cut cliff
Sea cave
Estuary
Oceanic and Continental Crust
• Continental margins (Figure 16-12)
–
–
–
–
–
Continental shelf (avg. width 60 km)
Continental slope (10% drop off, edge of continent)
Submarine canyons (cut by turbidity currents)
Continental rise (gentle slope of sediment)
Trenches ( no continental rise can be 11 km deep)
• Continental crust is 40 km thick on average
• Oceanic crust is 7 km thick on average
Ocean Basins
• Abyssal plains - large flat areas covered
by (hundreds of meters thick) sediments
• Deep sea trenches (most on the edges of
the Pacific Ocean). Trenches are 100 km
wide and extend thousands of km.
Ocean floor bumps
• Mid-ocean ridges
– 1500 m tall
– Thousands of km wide
– Many thousands of km long
• Rifts extend along the ocean ridges in
many places
• Volcanic activity and earthquakes are
common at the mid-ocean ridges
More interesting bumpy stuff
• Isolated seafloor volcanoes
• There are tens of thousands of these
mountains dotted across the ocean floor
• Some break the surface of the water as
volcanic islands (Azores, Iceland, etc.)
• Others are extinct volcanoes
– Seamounts - submerged volcanoes
– Guyots - flat top mountains
Marine sediments
Reference maps:
Physiographic Map of
Earth on pages 912-3 in
text.
NOAA Marine Sediment
Thickness Map
Ocean Floor
• Examine and interpret
bathymetric,
topographic, and
relief data.
Tsunami
• Dec 26, 2004
• Caused by
•
•
earthquake of
magnitude 9.0
Fourth strongest
quake since 1900
Off the coast of
Sumatra, Indonesia
Tsunami animation
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.