Chapter 16

The Marine Environment

Longshore currentsLongshore currents

• Waves usually approach the beach at an angle

• Water recedes parallel to the beach.

• Waves usually approach the beach at an angle

• Water recedes parallel to the beach.

Longshore currentsLongshore 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.

• 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 SeawallsJetties and Seawalls

Erosional landformsErosional 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.

• 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 landformsErosional landforms

• Sea stacks

• Wave cut platform

• Wave cut cliff

• Sea caves

• Sea stacks

• Wave cut platform

• Wave cut cliff

• Sea caves

BeachesBeaches

• Beaches can be mud, sand, pebbles, cobbles, gravel, or rocky.

• Color of the sand depends on material eroded.

• Beaches can be mud, sand, pebbles, cobbles, gravel, or rocky.

• Color of the sand depends on material eroded.

BeachesBeaches

• Hawaii has black sand beaches in some locations.

• The eroded material is dark volcanic rock.

• Hawaii has black sand beaches in some locations.

• The eroded material is dark volcanic rock.

BeachesBeaches

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

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

EstuariesEstuaries

• 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)

• 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 landformsDepositional landforms

• Spit

• Which way is the current flowing?

• Spit

• Which way is the current flowing?

Depositional landformsDepositional landforms

• Tombolo• Tombolo

Depositional landformsDepositional landforms

• Baymouth bar• Baymouth bar

Depositional landformsDepositional landforms

• Lagoon

• Bay

• Lagoon

• Bay

Depositional landformsDepositional landforms

• Barrier Island• Barrier Island

*** Coastal landforms*** Coastal landforms

• Depositional

• Beach

• Spit, Baymouth bar

• Tombolo

• Bay or Lagoon

• Barrier Island

• Longshore bar

• Sand bar

• 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

• Erosional

• Beach

• Sea stack

• Wave cut platform

• Wave cut cliff

• Sea cave

• Estuary

Oceanic and Continental CrustOceanic 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

• 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 BasinsOcean 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.

• 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 bumpsOcean 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

• 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 stuffMore 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

• 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 sedimentsMarine sediments

Reference maps:

Physiographic Map of Earth on pages 912-3 in text.

NOAA Marine Sediment Thickness Map

Reference maps:

Physiographic Map of Earth on pages 912-3 in text.

NOAA Marine Sediment Thickness Map

Ocean FloorOcean Floor

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

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

TsunamiTsunami

• Dec 26, 2004

• Caused by earthquake of magnitude 9.0

• Fourth strongest quake since 1900

• Off the coast of Sumatra, Indonesia

• 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 aCinepak decompressor

are needed to see this picture.