geo hw 15

4. Beaches downcurrent from a groin tend to ____________ because of beach drift.

erode

Why is it warmer in most of Europe than in northern California even though both are on the east side of an ocean and Europe is at higher latitude than California?

California is affected by a cold offshore current, whereas Europe has the warm north Atlantic current, the continuation of the Gulf Stream.

Examine the Big Sur Gigapan image to see if you can observe some of the specific erosional and depositional features that you just learned about.

left to right sea arch marine terrace sea stacks wave-cut cliffs

What is the longshore current?

water forced by waves to move along the shore

How is an 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.

The first step to exploring a landscape is to locate the areas on a map. Once you have done this, then you can consider the broader geologic context of the area to aid in your interpretation of the coastline. Now, determine where you are (your field site) in the world. Choose the map that best locates the coastline.

This site is located along the northern California coast in Big Sur, just south of the San Francisco Bay Area.

What is the Coriolis effect?

the deflection of objects to the right in the Northern Hemisphere, and to the left in the Southern Hemisphere

What is the wavelength?

the distance between consecutive wave crests or troughs

What are tides?

the regular daily rises and falls in sea level caused by the gravitational attraction of the Moon and Sun on Earth

Which rock types would you expect to be deposited on top of limestone if sea level falls and then rises?

mud followed by limestone

What do we call the tide that occurs when destructive interference between lunar and solar bulges produces a small tidal range?

neap tide

The energy that drives surface ocean currents such as the Gulf Stream comes from ________

prevailing winds

Deep ocean currents ___.

result from changes in water density (due to temperature and salt content)

Which rock types would you expect to see deposited if sea level rises and then falls?

sand covered by mud covered by sand

If the sediment that makes up the beaches of Cape Cod were to lithify, what kind of rock would it become?

sandstone

Which feature results from the collapse of a sea arch?

sea stack

Which way would an airplane deflect if flying from the west coast of South Africa to the east coast of South Africa?

to the north

Which way would an airplane deflect if flying from the North Pole toward the equator?

to the right

How would an object in Earth's atmosphere be deflected as a result of Earth's rotation?

to the right in the Northern Hemisphere, and to the left in the Southern Hemisphere

Which way would an airplane deflect if flying from the West Coast of the United States to the East Coast of the United States?

to the south

4. Freezing seawater at _________ leads to increases in salinity and density.

high latitudes

Why does the Moon generate larger tidal forces than the Sun?

Although the Sun is bigger, the Moon is much closer.

Based on the diagram below, at what location would you expect the highest high tide to occur?

A

Palm trees associated with the subtropics can be found at the northern tip of the British Isles in Scotland. This is due to the transfer of heat from the ________________

North Atlantic current.

Which of the following moon stages is correlated with Spring tides?

all black all white

Which of the following moon stages is correlated with Neap tides?

black and white white and black

What is the wave height?

the distance between the highest and lowest part of the wave

Which way would an airplane deflect if flying from the East Coast of the United States to the West Coast of the United States?

to the north

Which way would an airplane deflect if flying from the east coast of South Africa to the west coast of South Africa?

to the south

Which way would an airplane deflect if flying from the North Pole toward the equator?

to the west

Determine the general wave and longshore sediment transport (or beach drift) directions by determining where the sand is piling up versus where it is eroding. Apply what you have learned and deduce what you can about wave direction, sediment transport, and shore stabilization to correctly label the various components highlighted in the image. Drag the appropriate labels to their respective targets. Note that not all labels will be used.

top to bottom beach drift direction groins incoming wave direction longshore current direction

3. The pier-like structures ___________ sand that is moving parallel to the shore.

trap

How many spring and neap tides will a tide-recording station experience in a given month?

2 spring tides and 2 neap tides

Which of the following distances represents one wavelength of the wave set drawn below?

A to C represents a wavelength.

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 is a cave created in a cliff face along a sea coast?

Wave action erodes areas of weakness in rock in a sea cliff.

Which of the following statements about wave period is most accurate?

Wave period is the inverse of wave frequency.

When a headland of resistant bedrock extends out into the ocean, which statement best describes wave action in proximity to the headland?

Wave energy is focused on the headland.

While you are playing Frisbee in the surf zone with another person, your friend watches while sitting on the beach nearby. After a while, you look up at the beach and realize you are no longer directly in front of your friend, who remained stationary on the beach all the while—you are still in the surf zone, but 30 to 40 yards from where you started. What is the correct reason for this movement?

Waves were coming at the shore at an angle. The longshore current moved downstream to that angle and pushed you in that direction.

How shallow must the ocean floor be for waves to start to "feel bottom" for a wave set with a wavelength of 20 feet?

Waves will "feel bottom" when the ocean floor is 10 feet below the surface.

How are wave period and wavelength related?

Waves with shorter periods have shorter wavelengths.

A spring tide occurs ________.

about 26 times per year, at every full and new moon

Which process is directly responsible for the development of notches, cliffs, and platforms?

abrasion

Warm ocean currents ___.

are warmer than the surrounding water

Which way would sediment move if NO beach drift existed?

at an angle to shore

The zigzag movement of sand grains along a beach is ________.

both caused by obliquely breaking waves and called beach drift

3. Waters along the California coast are colder than those along the mid-Atlantic shore of the U.S. because ______________ occurs as surface waters move away from the coast.

coastal upwelling

Equatorial currents that are part of the subtropical gyres flow ___. Equatorial counter currents between the gyres flow ___ .

east to west; west to east

What is the name of the gigantic boulders left behind as the glaciers receded?

erratics

Surface ocean currents ___.

form large rotating gyres in the major ocean basins are driven by winds are influenced by Coriolis effect

Cool ocean currents ___.

generally flow from high latitudes towards the equator

5. The photo of the New Jersey shore is an example of a __________

groin field

What do we call the tide that occurs when constructive interference between lunar and solar bulges produces a large tidal range?

spring tide

What is the crest of a wave?

the highest part of the wave

What is the trough of a wave?

the lowest part of the wave

What is the wave period?

the time it takes for one wavelength of a wave to pass a particular point

Which way would an airplane deflect if flying from the South Pole toward the equator?

to the left

We need to know how the coast is oriented on a local map before analyzing its landforms and processes. Mapping the coast will help us put landscape features and processes in the proper context. Choose the most accurate representation of where you are observing the shoreline in this Gigapan image.

you between west and north land between east and south

Based on the diagram below, at which locations would you expect low tides to occur?

B D

Barrier islands are key features of some coastlines that consist of low ridges of sand that parallel the shore. They are common along the Atlantic and Gulf Coastal Plains and are characterized by sand dunes and quiet lagoons. The location and features of barrier islands make them popular locations for coastal development. However, because these islands face the open ocean, they tend to be exposed to the full force of those occasional, powerful ocean storms. A friend is considering purchasing a vacation home on a barrier island. Given what you've learned about the impact of waves on coastal landforms, what information and advice could you offer your friend? Select the two statements that apply.

Barrier islands tend to experience significant erosion and deposition of sand. Mitigating these effects is extremely difficult and costly. Your friend would be wise to reconsider. A home on a barrier island is likely to take the full brunt of storm waves, making it a risky proposition. Your friend should think twice before purchasing.

Which one of the following statements regarding active and/or passive margins is NOT true?

Cape Cod represents an active margin, as evidenced by its large sand dunes.

How are changes in sea level recorded in rock?

Rock type changes vertically.

How did sea level change to produce this sequence of rocks?[TOP: Mud, MID1: Limestone, MID2: Mud, BOTTOM: Limestone]

Sea level fell, then rose, and then fell again.

How did sea level change to produce this sequence of rocks?[TOP: Sand, MID: Mud, BOTTOM: Limestone]

Sea level fell.

How did sea level change to produce this sequence of rocks?[TOP: Limestone, MID: Mud, BOTTOM: Sand]

Sea level rose.

How would you expect sediment to change as you walk from shore into the ocean?

Sediment generally changes from sand to mud to limestone.

Recall that global winds impact the direction of surface ocean currents. Examine the following map showing the Atlantic Ocean off the west coast of Africa. The direction of the surface current and the prevailing wind do not coincide. What can explain this discrepancy?

The Coriolis effect deflects ocean currents in the Southern Hemisphere to the left due to Earth's rotation. Because the current is located in the Southern Hemisphere, the subtropical gyre pulls the current in a counterclockwise direction.

A set of waves are moving from east to west. Assuming the boat is in deep water, which of the following would describe the motion of a boat during the passage of these waves?

The boat would move up and down in the water.

Now we can apply our observations and knowledge of how emergent coastlines evolve to anticipate the future issues for this particular coastline.

The gray house above the wave-cut cliff and the coastal road may be in peril as the coastline continues to cut back landward by wave action and continued cliff retreat

During a visit to the beach, you get in a small rubber raft and paddle out beyond the surf zone. You become tired, so you stop and take a rest. Describe the movement of your raft beyond the surf zone.

The raft's net movement is not toward the shore compared to the surf zone. The raft moves in a circle, and it returns to essentially the same place.

Why are high tides found simultaneously on opposite sides of Earth?

The tidal bulges occur on both sides of Earth that are aligned with the tide-generating body.

2. ______________________ is caused by density changes near the poles and equator.

Thermohaline circulation

Based on the moon phase shown below, select which special tide has occurred most recently and which special tide will occur next.

A spring tide will occur next. A neap tide has most recently occurred.

How does a sea stack form?

A stack forms when a sea arch collapses, leaving a vertical column of rock offshore.

In the long term, what do beach drift and longshore current do?

Move sediment parallel to the shoreline

thin peninsula called a spit extends beyond the bluffs of the outer beach on Cape Cod. What has caused this spit to form?

Sand from the bluffs is carried and deposited by longshore currents.

How did sea level change to produce this sequence of rocks?[TOP: Limestone, MID1: Mud, MID2: Sand, BOTTOM: Mud]

Sea level fell and then rose.

Which ocean current is the only one to completely circle Earth?

The West Wind Drift

1. The pier-like structures are installed _______________to the shore.

perpendicular

The subtropical gyres ___.

play a large role in climate

If the wavelength of a set of waves is 20 feet long, how deep is the wave base?

10 feet below the surface

Regional climate and local geology greatly affect the appearance and behavior of coasts. Climatic and geologic factors that influence coasts include: Proximity to rivers that deliver a great amount of sediment The deformation rate or absence of tectonic activity The erosion susceptibility of the bedrock Frequency of intense storms, and prevailing wind direction Configuration of the coastline and nearshore areas In order to understand the complexities of coastlines, a classification system using sea level as a reference is used. Geologists have created two general categories for coastal zones that describe how they change relative to sea level: whether the coast appears to be emerging from underneath the water or submerging below it. Emergent coasts appear to be moving up out of the water and develop as a result of tectonic uplift or sea level fall. Submergent coasts appear to be sinking and are created when the land is subsiding or sea level is rising. Emergent coasts are formed by tectonic uplift or sea level fall; therefore, erosion processes play an important role in shaping them. As a result, we might see steep cliffs and previously submerged features now above water level. Conversely, because submergent coasts are the result of subsidence or sea level rise, we expect depositional processes (such as large accumulations of sediment) and inundation by water of rivers entering the sea to play important roles in shaping them.

Emergent coasts are likely to be found in areas experiencing active tectonic uplift. Frequent flooding is a characteristic of rivers that flow to submergent coastlines.

Wave action creates and changes beaches drastically. The sand that makes up beaches is transported along the shoreline by the following wave action. Waves typically approach shorelines at an angle rather than head on. Waves that hit the shoreline are then refracted perpendicular to the shoreline. The change in direction of a wave once it hits the shoreline transports sand grains along the shore. Water flow along shorelines is described with the following terms. Longshore drift is the net flow of water along the shore that results from waves that refract along the shoreline. Longshore drift is parallel to the shoreline in one direction. The direction roughly points towards the same general direction as sand transport and incoming waves. Upstream refers to the direction opposite of longshore drift. Rip currents are strong surface currents. Water that refracts from the shoreline can return out to sea along the surface or along the ocean bottom. Rip currents are the retreating waves that return along the surface. This type of current can be very dangerous to unwary swimmers. The image below shows the movement of water and sand along a beach.

left to right incoming wave direction path of sand particles upstream direction longshore drift beach drift and net movement of sand grains

Which rock types would you expect to be deposited on top of limestone if sea level rises and then falls?

limestone followed by mud

When sea ice forms in high latitudes, the sea ice has ________.

lower salinity than the ocean waters it forms from

2. The purpose of the pier-like structures is to _______________ the beach and prevent erosion.

maintain or widen

Wave-cut platforms are particularly important landforms because they indicate an elevation change of sea level and/or land surface. These landforms are identified by their relatively flat, seaward sloping surfaces. The steps in which they form and change are: Waves erode the cliff at its base. This leads to cliff collapse. The rocks detached from the cliff face are eventually transported away by waves. Now a new face of the cliff is exposed. It is eroded in a similar fashion. Over time, progressive cliff erosion leaves a nearly flat surface. If the region is undergoing tectonic uplift, the platform is raised above sea level. This can result multiple levels of wave-cut platforms. After one is uplifted above sea level, another one will form at sea level. Place the formation steps of a wave-cut platform in order from oldest to youngest. Be sure to consider the formation of two generations of wave-cut platforms and assume that sea level does not change during their formation.

oldest wave-driven erosion is focused on exposed bedrock cliffs cliff retreat continues from repeated undercutting of wave-cut cliffs that ............ a wave cut platform is formed after some time a wave cut platform is uplifed above the present day sea level .......... a lower elevation wave cut platform ..... yougest