Oceanography Chapter 10
Of the following characteristics or features, which is/are associated with depositional shores?
- Bay-mouth bars - High sediment supply - A location near a large delta - The formation of barrier islands - A large sand spit
Of the following statements about groins, which is/are true?
- Groins can be constructed out of large blocky rocky material (rip-rap) or of sturdy wood pilings. - Groins can be singular or many.
Of the following statements about the physical characteristics of coastal oceans, which is/are true?
- In middle-latitude coastal oceans where evaporation is high, a halocline can develop. - Onshore wind and coastal runoff create geostrophic currents that flow northward along western North America. - In low-latitude areas where there is no mixing, surface water temperatures can be very high. - In high-latitude areas, the coastal ocean is isothermal (has a uniformly low temperature from surface to deeper waters).
How is arch formed along a sea coast?
An arch forms when a sea cave breaks through a headland or where two sea caves coalesce as they erode back due to wave action.
What is the correct order of beach features as you move from the coast toward offshore?
Berm, beach face, longshore trough, longshore bar
On this perspective view of a barrier island, match the correct letter to each of the following features.
C: Peat bed B: Dune E: Ocean beach D: Barrier flat F: Lagoon A: Salt marsh
Why does the crust subside slightly on either side of a melting glacier?
Crust under the glacier rises as the ice melts. This allows mantle on either side of the glacier to move to areas under the glacier.
During summertime, there is much more sand on the beach.
During summertime, there is much more sand on the beach
What is the most obvious difference between summertime and wintertime beaches?
During summertime, there is much more sand on the beach
By looking at the degree of erosion of the platforms, arrange the three platforms (B, D, and F) in order from oldest (formed longest ago) to youngest (formed most recently).
F,D,B
This image shows a variety of beach and shoreline features. Match the correct letter to the regions and/or features listed below.
H: Longshore Bar A: Berm G: Beach B: Offshore F: Coast D: Wave-cut cliff C: Shore I: Beach face E: Nearshore
If the current trend in the loss of coastal wetlands does not change, what consequence(s) would you predict?
Increased loss of marine fisheries
At the mouth of the Amazon River in Brazil, how would the coastal waters be characterized with respect to temperature and salinity?
Isothermal with a strong halocline
Why does the beach in the video look the way that it does during wintertime?
Large waves move sand offshore onto longshore sand bars and create a rocky beach
Why does the crust uplift slightly on either side of a growing glacier?
Mantle under the glacier is pushed aside by sinking crust. This mantle pushes up the crust on either side of the glacier.
In the long term, what do beach drift and longshore current do?
Move sediment parallel to the shoreline
You are an engineer assigned to design a solution to protect a historic landmark threatened by coastal erosion. What scenario would have the least impact on natural coastal processes and be the most cost effective?
Relocate the structure
What would you expect to happen to sea level along the Antarctic coastline if the ice cap covering the continent melted?
Sea level would decrease due to isostatic adjustment.
Why does the beach shown in the video look the way that it does during summertime?
Small waves move sand up the beach face and create a wide, sandy beach
Normally, beaches have the greatest amount of sand on the berm near the end of______.
Summer
The Pacific coast, excluding Alaska, has the lowest average erosion rate in the U.S., despite significant beach starvation and localized erosion. Which of the following factors accounts for this low average?
Tectonic emergence
What will happen to the crust as a glacier grows?
The crust under the glacier will sink into the mantle.
Evaluate the ridges at placemark E in the context of what we have explored thus far. Which of the following statements best describes the nature of those ridges?
These small ridges above a plain are similar to the sea stacks present offshore.
How is a cave created in a cliff face along a sea coast?
Wave action erodes areas of weakness in rock in a sea cliff
Features of a depositional coast may include spits, barrier islands, tombolos, and _______.
deltas
Beach joggers prefer to run on the __________.
beach face
You own a beachfront lot that has been experiencing erosion due to beach starvation. Your neighbor to the north (up-current) has the same problem, so he gets permission to build a groin just north of your property line. Your response would probably be to __________.
get permission to build a groin of your own near the southern boundary of your property
Southern California beaches would have more sand if _______.
dams were removed from streams flowing to the coast
Geologic evidence suggests that eustatic (global) sea level rises have been caused by __________.
rapid seafloor spreading at divergent plate boundaries
Which of the following describes an estuary located at the mouth of a high-volume river where freshwater flows to the ocean over a layer of dense saline water? Select only one answer.
salt wedge estuary
Which term best describes the landforms at the placemarks labeled C?
sea stacks
San Francisco Bay is a _______ estuary.
tectonic
What is isostasy?
the rising and sinking of Earth's crust relative to the mantle in response to the redistribution of mass on the surface
For how long will land rebound after a glacier melts?
thousands of years
What is the longshore current?
water forced by waves to move along the shore
The California coast in this region displays a variety of landforms formed by both erosion and sediment deposition. Which term best describes the seafloor structure around placemarks A and B?
wave-cut beach
Of the following statements about longshore transport (longshore drift), which is/are true?
- Longshore transport can change direction depending on which direction the waves approach the beach. - Longshore transport moves sediment upcoast or downcoast along the beach. - Longshore transport moves sediment in a zigzag path
Of the following characteristics or features, which is/are associated with erosional shores?
- Rocky coasts - Tectonic activity - Wave-cut benches and marine terraces - A coastline with lots of rugged headlands
Of the following statements about coastal regions and landforms, which is/are true?
- The berm is located in the backshore area. - Most of the beach face is exposed during the lowest tides and covered during the highest tides. - The beach face is the wet, sloping surface in the foreshore area. - The area of a beach above the shoreline is often called the recreational beach. - The berm is affected by storm waves but is typically dry and relatively flat.
Of the following statements about coastal wetlands, which is/are true?
-Scientists estimate that, globally, 50% of all coastal wetlands have disappeared in the past century. -Mangrove swamps are a type of coastal wetland that can protect shorelines from erosion. - Coastal wetlands are good at cleansing water of agricultural runoff, toxins, and other pollutants. - Coastal wetlands often serve as important nursery areas for many species of fish.
Of the following statements about global sea level, which is/are true?
-Sea level is affected by the amount of ice in polar ice caps on land. - Sea level has risen about 120 meters (400 feet) in the past 18,000 years. - When seawater warms, it thermally expands and occupies more volume, so global sea level rises. - When seawater cools, it contracts and occupies less volume, so global sea level is lowered.
Which feature of barrier islands provides evidence for a rise in sea level?
A peat outcrop
How does a sea stack form?
A stack forms when a sea arch collapses, leaving a vertical column of rock offshore.
What condition would create a weak longshore current?
A wave set approaching parallel to the shore head-on
The image below depicts shoreline features characteristic of depositional coasts. Match the correct letter to each of the following features.
A: Tombolo C: Barrier island B: Spit D: Bay barrier F: Delta E: Lagoon
Which estuary is most likely to be highly stratified?
Alaskan fjord
On this diagram showing a perspective view of California's Santa Barbara Harbor, match the correct letter to each of the following items.
B: Arrow that points in the direction of a longshore Drift D: Breakwater A: Area of sand deposition E: Area threatened by erosion after construction of the breakwater C: Arrow that points in the OPPOSITE direction of longshore drift F: Dredge
The image below depicts shoreline features characteristic of erosional coasts. Match the correct letter to each of the following features.
B: Sea arch D: Headland H: Sea cave G: Blowhole A: Coves F: Uplifted marine terrace C: Wave-cut bench E: Sea stack
In general, what do beaches look like at the end of winter?
Beaches tend to have a narrow berm and a prominent longshore bar
In general, what do beaches look like at the end of summer?
Beaches tend to have a wide berm and no longshore bar
Each of the platforms and the ridges at the placemarks labeled C and E were formed by wave action—the platform at placemark B is currently "under construction," and those at the placemarks labeled D and F are older. What must have happened to produce the three platforms you see here?
The land rose (or sea level dropped) in at least two episodes. First, after the platform (a wave-cut bench) at placemark F was formed, the land rose approximately 130 meters, and the platform at the placemarks labeled D and sea stacks at placemark E were formed. A second uplift of approximately 30 meters left the platform at the placemarks labeled D 30 meters above sea level. The construction of the platform at placemark B began then and continues today.
Let's compare the morphology of the land adjacent to the coastline to what we've observed along the seafloor. Which of the following statements best describes the topography/appearance of the land surface at the placemarks labeled D?
The landscape at the placemarks labeled D is a broad plain, similar to the topography of the seafloor at placemarks A and B.
Why does glacial subsidence NOT occur at the exact moment that a glacier forms?
The rate of subsidence is controlled by the rate at which mantle can flow.
Which of the following statements best describes the seafloor surface in this area?
The seafloor is relatively smooth, and the water is not deep at all.
How does the tide cycle affect erosion along a sea coast?
The tide cycle causes erosion to occur at different elevations along a sea coast
How would a beach be affected if a wide berm were protected from erosion during winter months?
The wintertime beach would look similar to the summertime beach
How are winter beaches different from summer beaches?
Winter waves are short and high, whereas summer waves are long and shallower
The coastal wetlands of Louisiana are being lost primarily because of __________.
a combination of subsidence and rising sea level
Of the following types of estuaries, which one has a relatively shallow mouth but is often narrow, long, and extremely deep? Select only one answer.
a drowned glacial valley called a fjord
How long does it take berms to become narrow and rocky after summer has passed?
a few weeks
Which way would sediment move if NO beach drift existed?
at an angle to shore
Important plants in a coastal wetland at 45°N latitude are most likely to be __________.
halophytic grasses and pickleweed
Southern California beaches in winter typically are narrow and rocky. That is because __________.
heavy winter wave activity moves the sand out to the longshore bar and uncovers the rocks underneath the sand
An isothermal temperature profile from surface to seafloor may exist in coastal ocean waters __________.
in either low-latitude waters or high-latitude waters