Physical Oceanography

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Chapter 16 The Marine Environment
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Longshore currents

• Waves usually approach the beach at an angle
• Water recedes parallel to the beach.

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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.

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Groins will catch sand carried by the Longshore
current.
Which way is the Longshore current flowing in
this picture?
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Jetties and Seawalls
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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.

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Erosional landforms

• Sea stacks
• Wave cut platform
• Wave cut cliff
• Sea caves

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Beaches

• Beaches can be mud, sand, pebbles, cobbles,
  gravel, or rocky.
• Color of the sand depends on material eroded.

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Beaches

• Hawaii has black sand beaches in some locations.
• The eroded material is dark volcanic rock.

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Beaches

• Florida and the Bahamas white and pink sand
  beaches are bits of local coral and sea shells.

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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)

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Depositional landforms

• Spit
• Which way is the current flowing?

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Depositional landforms

• Tombolo

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Depositional landforms

• Baymouth bar

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Depositional landforms

• Lagoon
• Bay

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Depositional landforms

• Barrier Island

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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

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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

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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.

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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

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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

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Marine sediments

• Reference maps
• Physiographic Map of Earth on pages 912-3 in
  text.
• NOAA Marine Sediment Thickness Map

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Ocean Floor

• Examine and interpret bathymetric, topographic,
  and relief data.

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Tsunami

• Dec 26, 2004
• Caused by earthquake of magnitude 9.0
• Fourth strongest quake since 1900
• Off the coast of Sumatra, Indonesia

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Tsunami animation