Ch 17 (Part II) SHORELINES

a) Wavesb)Longshore transportc) Erosional shoresd)Depositional shorese) Emergent and submergent shoresf) Sealevel rise

= orbital wave (waves of oscillation)

Energy advances

But:

Water does not!Water moves in circular orbits

=

erosion

Ocean WAVES

a) Wavesa) WavesShorelinesShorelines

Waves ‘feel’ bottom when it comes to within half of the wavelength

Wave length decreases, wave height increasesAt critical point the wave becomes too steep and breaksSurf sloshes onshore

Breaking WAVES

Fig. 17.13

a) Wavesa) WavesShorelinesShorelines

Summertime and wintertime beach conditions

Summertime beach Wintertime beach

a) Wavesa) Waves

Wave refraction strongly influences erosion and sediment transport

Waves travel more slowly in shallow water so they refract towards

the beach.

a) Wavesa) Waves

Waves refract around headlands, increasing

wave impact on headlands, decreasing it

on beaches. Fig. 17.13

Longshore transport • Swash is oblique,

backwash straight, causing beach drift of sediment along the shore

• Oblique waves also cause longshore currents parallel to beach

b) Longshore transportb) Longshore transport

Beaches = Rivers of sand!Beaches = Rivers of sand!

ShorelinesShorelines

Longshore currents and rip currents

Wave refraction along an irregular shoreline

• Wave energy is concentrated at headlands and dispersed in bays

• Causes erosion of headlands and creation of erosional features Figure 10-14b

c) Erosional Shoresc) Erosional ShoresShorelinesShorelines

Fig. Story 17.13

• Headland• Wave-cut cliff• Wave-cut

terrace (bench)

• Sea cave• Sea arch• Sea stack

c) Erosional Shoresc) Erosional ShoresShorelinesShorelines

ShorelinesShorelines

BEACHES

• Source of beach sediments

- rivers- cliff erosion- marine life

• Sand composition

d) Depositional Shoresd) Depositional Shores

Beaches

See Fig. 17.18

ShorelinesShorelines

BEACHES

• Source of beach sediments

- rivers- cliff erosion- marine life

• Sand composition

d) Depositional Shoresd) Depositional Shores

See Fig. 17.18

• Spit

• Bay barrier (baymouth bar)

• Tombolo

• Barrier island

• Delta

d) Depositional Shoresd) Depositional ShoresShorelinesShorelines

Emergent coasts

Develop because of uplift of an area or a drop in sea level

Features of an emergent coast– Wave-cut cliffs

– Wave-cut platforms

e) Emergent and submergent coastse) Emergent and submergent coasts

Uplifted, ancient wave-cut benches exposed in southern California

e) Emergent and submergent coastse) Emergent and submergent coasts

Submergent coast

Caused by subsidence of land adjacent to the sea or a rise in sea level

Features of a submergent coast– Highly irregular shoreline

– Estuaries – drown river mouths

e) Emergent and submergent coastse) Emergent and submergent coasts

Chesapeake Bay is a good example of a submergent coastline

e) Emergent and submergent coastse) Emergent and submergent coasts

f) Sea-level risef) Sea-level rise

Fossil fuel burning has added greenhouse gases to atmosphere

Sea-level rise: thermal expansion of seawater and ice-sheet melting, 4mm/yr, 20-90 cm during this century

Global warming follows(up to 0.6 C in past century)

Chapter 17: Earth beneath the ocean

The area labeled “W” is the __________.A. abyssal plainB. continental riseC. continental shelfD. continental slope   

WX

Y

Z

Chapter 17: Earth beneath the ocean

 

The area labeled “X” is the __________.A. abyssal plainB. continental riseC. continental shelfD. continental slope   

WX

Y

Z

Chapter 17: Earth beneath the ocean

 

The area labeled “Y” is the __________.A. abyssal plainB. continental riseC. continental shelfD. continental slope

WX

Y

Z

Chapter 17: Earth beneath the ocean

Which of the following statements is false?

A. Deep-sea sedimentation leaves a more continuous geologic record than continental sedimentation.B. The oceans lack folded and faulted mountains like those on continents.C. The oldest oceanic crust is much younger than the oldest continental crust.D. Weathering and erosion are more important in the oceans than on continents.

Chapter 17: Earth beneath the ocean

  

In which of the following locations would you most likely find outcrops of basalt on the ocean floor?

A. on the abyssal plainB. on the continental riseC. on the continental shelfD. on the flank of a rift valley

Chapter 17: Earth beneath the ocean

  

A traverse from North America across the Atlantic Ocean to continental Europe would reveal that the ocean floor ____________.

A. has high undersea mountains near both continents and is flat in the middleB. has deep trenches near both continentsC. has a number of active volcanoes along most of the width of the traverseD. is approximately symmetric about the Mid-Atlantic Ridge

Chapter 17: Earth beneath the ocean

 

Graded beds of sand, silt, and mud deposited on submarine fans are called ______.

A. alluvial fansB. dunesC. tillsD. turbidites

Chapter 17: Earth beneath the ocean

Which of the following materials would one expect to find on a continental shelf at a passive margin?

A. basaltB. pelagic sedimentsC. terrigenous sedimentsD. volcanic ash

Chapter 17: Earth beneath the ocean

What are foraminifera shells, the most abundant biochemically precipitated pelagic sediment, made of?

A. calcium carbonateB. silicon dioxideC. sodium chlorideD. iron sulfide

Chapter 17: Earth beneath the ocean

 

Which of the following forms a barricade between the open ocean and the main shoreline?

A. abyssal hillsB. barrier islandsC. guyotsD. wave-cut terraces

Chapter 17: Earth beneath the ocean

The zigzag motion that carries sand grains along a beach is known as ________.

A. longshore driftB. meanderingC. refractionD. turbidity