Ch 17 (Part II) SHORELINES
a) Waves
b) Longshore transport
c) Erosional shores
d) Depositional shores
e) Emergent and submergent shores
f) Sealevel rise
Shorelines
a) Waves
Ocean WAVES
= orbital wave (waves of
oscillation)
Energy advances
But:
Water does not!
Water moves in circular orbits
Shorelines
a) Waves
Breaking WAVES
Waves ‘feel’ bottom when it comes to within half of the
wavelength
Wave length decreases, wave height increases
At critical point the wave becomes too steep and breaks
Surf sloshes onshore
Fig. 17.13
a) Waves
Summertime and wintertime
beach conditions
Summertime beach
Wintertime beach
a) Waves
Wave refraction
strongly influences erosion and sediment transport
Waves travel more
slowly in shallow water
so they refract towards
the beach.
Waves refract around
headlands, increasing
wave impact on
headlands, decreasing it
on beaches.
Fig. 17.13
Shorelines
b) Longshore transport
Longshore transport
• Swash is oblique,
backwash straight,
causing beach drift of
sediment along the
shore
• Oblique waves also
cause longshore
currents parallel to
beach
Beaches = Rivers of sand!
Longshore currents and rip currents
Shorelines
c) Erosional Shores
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
Fig. Story 17.13
Shorelines
c) Erosional Shores
• Headland
• Wave-cut cliff
• Wave-cut
terrace
(bench)
• Sea cave
• Sea arch
• Sea stack
Shorelines
d) Depositional Shores
BEACHES
• Source of beach
sediments
- rivers
- cliff erosion
- marine life
• Sand composition
Beaches
See Fig. 17.18
Shorelines
d) Depositional Shores
BEACHES
• Source of beach
sediments
- rivers
- cliff erosion
- marine life
• Sand composition
See Fig. 17.18
Shorelines
d) Depositional Shores
• Spit
• Bay barrier
(baymouth
bar)
• Tombolo
• Barrier island
• Delta
e) Emergent and submergent coasts
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 coasts
Uplifted, ancient wave-cut benches exposed in southern California
e) 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 coasts
Chesapeake Bay is a good
example of a submergent coastline
f) Sea-level rise
Fossil fuel
burning
has added
greenhouse gases to
atmosphere
Global warming
follows
(up to 0.6 C in past century)
Sea-level rise:
thermal expansion of
seawater and ice-sheet
melting, 4mm/yr, 20-90 cm
during this century
Chapter 17: Earth beneath the ocean
Y
W
X
Z
The area labeled “W” is the __________.
A. abyssal plain
B. continental rise
C. continental shelf
D. continental slope
Chapter 17: Earth beneath the ocean
Y
W
X
Z
The area labeled “X” is the __________.
A. abyssal plain
B. continental rise
C. continental shelf
D. continental slope
Chapter 17: Earth beneath the ocean
Y
W
X
Z
The area labeled “Y” is the __________.
A. abyssal plain
B. continental rise
C. continental shelf
D. continental slope
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.
B.
C.
D.
on the abyssal plain
on the continental rise
on the continental shelf
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
middle
B. has deep trenches near both continents
C. has a number of active volcanoes along most of the width of the
traverse
D. 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.
B.
C.
D.
alluvial fans
dunes
tills
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.
B.
C.
D.
basalt
pelagic sediments
terrigenous sediments
volcanic ash
Chapter 17: Earth beneath the ocean
What are foraminifera shells, the most abundant
biochemically precipitated pelagic sediment, made of?
A.
B.
C.
D.
calcium carbonate
silicon dioxide
sodium chloride
iron sulfide
Chapter 17: Earth beneath the ocean
Which of the following forms a barricade between the open ocean and
the main shoreline?
A.
B.
C.
D.
abyssal hills
barrier islands
guyots
wave-cut terraces
Chapter 17: Earth beneath the ocean
The zigzag motion that carries sand grains along a beach is known as
________.
A.
B.
C.
D.
longshore drift
meandering
refraction
turbidity