What landforms are created at divergent boundaries

LAB MODULE 13: PLATE TECTONICS

Note: Please refer to the GETTING STARTED module to learn how to maneuver through, and how to answer the lab questions, in the Google Earth (GE.gif) component.

KEY TERMS

You should know and understand the following terms:

Continental Drift

Pacific Ring of Fire

Reverse Fault

Earthquakes

Pangaea

Subduction

Hotspots

Plate Convergence

Transform Fault

Normal Fault

Plate Divergence

Overthrust fault

Plate tectonics

LAB MODULE LEARNING OBJECTIVES

After successfully completing this module, you should be able to do the following tasks:

· Explain the theory of plate tectonics

· Explain the theory of continental drift

· Identify and describe types of plate movement

· Identify and describe the three types of volcanoes

· Explain the concept of hotspots

· Compute the rates of plate movement

· Identify and describe the different types of faults

INTRODUCTION

This module examines plate tectonics. Topics include continental drift, tectonic landforms, plate boundaries, faults and hotspots. While these topics may appear to be disparate, you will learn how they are inherently related. The module starts with four opening topics, or vignettes, which are found in the accompanying Google Earth file. These vignettes introduce basic concepts of the internal structure of the Earth. Some of the vignettes have animations, videos, or short articles that will provide another perspective or visual explanation for the topic at hand. After reading the vignette and associated links, answer the following questions. Please note that some links might take a while to download based on your Internet speed.

GE.gif Expand the INTRODUCTION folder and then check Topic 1: Introduction.

GE.gif Read Topic 1: Introduction

Question 1: Based on this map, what is one continent in which there are two (or more) plates?

A. North America

B. Europe

C. Asia

D. Africa

GE.gif Read Topic 2: Continental Drift

Question 2: What was discovered in Antarctica that solidified Wegener’s theory of continental drift?

A. Snow and ice

B. Mineral deposits

C. Tropical plant fossils

D. Extinct volcanoes

GE.gif Read Topic 3: Tectonic Landforms

Question 3: Where do scientists think the next major ocean will be formed?

A. Gulf of Mexico

B. Iceland

C. Australia

D. East Africa

GE.gif Read Topic 4: Human Interaction

Question 4: Based on the article, which is not a reason why humans are drawn to plate boundaries.

A. Nice scenery

B. Geothermal energy

C. Fertile soil

D. Ore deposits

GE.gif Collapse and uncheck the Introduction folder. GLOBAL PERSPECTIVE

GE.gif Expand GLOBAL PERSPECTIVE. Double-click and select Tectonic Plate Boundaries and Names to display the names on the globe of the major tectonic plates.

Millions of humans live near the major tectonic plate boundaries. The potential dangers of living on or near a plate boundary include earthquakes, volcanoes, and tsunamis. However, these natural hazards do little to discourage people from settling in these cities, especially if the region has economic, religious, political or social importance.

GE.gif Expand and select Major Cities. Double-click and select Question 5. When you arrive at your destination, find the information to fill in the blanks below. Choose the two closest tectonic plates. Repeat this for Questions 5 to 8.

Question 5: City: San Francisco

Two closest tectonic plates

A. Pacific/North America

B. Pacific/Californian

C. North American/California

D. Pacific/Juan de Fuca

Question 6: City: Taipei, Taiwan

Two closest tectonic plates

A. Philippine/Taiwan

B. Taiwan/China

C. Philippine/China

D. Eurasian/Philippine

Question 7: City: Jerusalem, Israel

Two closest tectonic plates

A. Arabian/Eurasian

B. Mediterranean/Eurasian

C. African/Arabian

D. African/Eurasian

Question 8: City: Karachi, Pakistan

Two closest tectonic plates

A. Indian/Eurasian

B. Arabian/African

C. Pakistani/Indian

D. Burmese/Eurasian

GE.gif Collapse and uncheck the GLOBAL PERSPECTIVE folder.

PLATE BOUNDARIES AND MOVEMENTS

In general, tectonic plate boundaries are classified as converging, diverging, and transform, while tectonic plate types are classified as either oceanic or continental. The following descriptions of plate boundaries and movements will help you answer Questions 10 to 23.

Converging Boundaries

When an oceanic plate and a continental plate converge (Figure 1), the result is subduction, because the oceanic plate slides under the continental plate. Mountain ranges of volcanoes are created by magma from the melting oceanic plate rising to (and through) the continental crust. Deep oceanic trenches typically parallel the coast.

Description: GE.gif Expand the PLATE BOUNDARIES folder and then click Subduction Animation to view an animation of this type of convergence boundary.

Figure 1. Oceanic-continental convergence (USGS).

Figure 2. Continental-continental convergence (USGS).

When two continental plates converge (Figure 2), compression and uplift occur at the boundary to form mountain ranges. Continental-continental convergence mountains are not comprised of volcanoes and thus contrast the orogeny of mountain ranges produced by oceanic-continental convergence.

When two oceanic plates converge (Figure 3), one subducts under the other and the result is a deep ocean trench. In some cases, under sea volcanoes format these boundaries. Over millions of years, these oceanic-oceanic convergence boundaries produce volcanoes that reach the surface and form a chain of islands shaped in an arc.

Figure 3. Oceanic-oceanic convergence (USGS).

Diverging Boundaries

As the name implies, diverging boundaries occur where plates are moving away from each other. If the plates are oceanic, the result can be an underwater mountain range which follows the plate boundaries. If the plates are continental, the initial result is the creation of a valley or rift. Given enough time, these valleys or rifts might be submerged, forming long, narrow seas.

Transform Boundaries

Transform boundaries occur when two plates move horizontally past each other. The boundary, or fault, between the two plates can be several miles wide. Friction between the two plate boundaries can build up tectonic stress, which can be released instantaneously into the Earth’s crust in the form of an earthquake.

Description: GE.gif Expand the Boundaries folder, check the Plate Boundaries folder, and then doubleclick Boundary A.

Based on the descriptions of plate boundaries and movement provided, identify Boundaries A through G:

Question 9: Boundary a.gif _________

A. Continental-continental convergent

B. Continental-oceanic convergent

C. Oceanic-Oceanic convergent

D. Oceanic divergent

E. Continental-continental divergent

F. Transform

Question 10: Why did you choose this answer?

A. Red Sea is shrinking because two continental plates are coming together.

B. Red Sea plate is subducting under the Arabian Plate

C. The Arabian and African plates are moving away from each other, creating the Red Sea

D. The African plate is subducting under the Arabian Plate, closing off the Red Sea to the Indian Ocean

Description: GE.gif Doubleclick Boundary B.

Question 11: Boundary b.gif _________

A. Continental-continental convergent

B. Continental-oceanic convergent

C. Oceanic-Oceanic convergent

D. Oceanic divergent

E. Continental-continental divergent

F. Transform

Question 12: Why did you choose this answer?

A. Himalayas were formed by Indian plate riding over the Eurasian plate

B. Himalayas were formed by the Eurasian plate riding over the Indian plate

C. Himalayas were formed by the Indian and Eurasian plates colliding

D. Himalayas were formed by the Indian and Eurasian plates moving apart

Description: GE.gif Doubleclick Boundary C.

Question 13: Boundary c.gif _________

A. Continental-continental convergent

B. Continental-oceanic convergent

C. Oceanic-Oceanic convergent

D. Oceanic divergent

E. Continental-continental divergent

F. Transform

Question 14: Why did you choose this answer?

A. Mid-Atlantic ridge was created by North American and African plates colliding

B. Mid-Atlantic ridge was created by South American and African plates colliding

C. Mid-Atlantic ridge was created by North American plate subducting under the Eurasian plate

D. Mid-Atlantic ridge was created by North American and Eurasian plates moving apart and the South American and African plates moving apart.

Description: GE.gif Doubleclick Boundary D.

Question 15: Boundary d.gif _________

A. Continental-continental convergent

B. Continental-oceanic convergent

C. Oceanic-Oceanic convergent

D. Oceanic divergent

E. Continental-continental divergent

F. Transform

Question 16: Why did you choose this answer?

A. The Pacific and South American Plates are moving apart, forming a deep trench

B. The Pacific and South American plates are colliding forming the Andes Mountains

C. The Nazca plate is subducting under the South American plate, forming a deep trench

D. The South American plate is subducting under the Pacific plate, forming a deep trench

Description: GE.gif Doubleclick Boundary E.

Question 17: Boundary e.gif _________

A. Continental-continental convergent

B. Continental-oceanic convergent

C. Oceanic-Oceanic convergent

D. Oceanic divergent

E. Continental-continental divergent

F. Transform

Question 18: Why did you choose this answer?

A. The Pacific and North American Plates are moving apart, forming a deep trench

B. The Pacific and North American plates are colliding forming the Andes Mountains

C. The Pacific plate is subducting under the North American plate, forming a deep trench

D. The North American plate is subducting under the Pacific plate, forming a deep trench

Description: GE.gif Doubleclick Boundary F.

Question 19: Boundary F.gif _________

A. Continental-continental convergent

B. Continental-oceanic convergent

C. Oceanic-Oceanic convergent

D. Oceanic divergent

E. Continental-continental divergent

F. Transform

Question 20: Why did you choose this answer?

A. The two plates are colliding, creating a series of lakes in Eastern Africa

B. The two plates are moving apart creating a series of lakes in Eastern Africa

C. The two plates are sliding past each other creating a series of lakes in Eastern Africa

D. The two plates are colliding and shrinking the lakes in Eastern Africa

Description: GE.gif Doubleclick Boundary G.

Question 21: Boundary G.gif _________

A. Continental-continental convergent

B. Continental-oceanic convergent

C. Oceanic-Oceanic convergent

D. Oceanic divergent

E. Continental-continental divergent

F. Transform

Question 22: Why did you choose this answer?

A. The Pacific and Philippine plates are moving apart, forming a deep trench

B. The Pacific and Philippine plates are colliding forming the Andes Mountains

C. The Pacific plate is subducting under the Philippine plate, forming a deep trench

D. The Philippine plate is subducting under the Philippine island chain, forming a deep trench

GE.gif Collapse and uncheck the PLATE BOUNDARIES folder.

EARTHQUAKES

When tectonic stresses from moving plates along boundaries and fault lines become too great, there can be a sudden release of energy which is manifested as an earthquake. The foci (where the earthquake originates) is often deep within the Earth’s lithosphere, while the epicenter, located vertically above the focus, is found at the Earth’s surface.

Earthquakes occur daily, yet we are not always able to feel them. Seismic waves (p and s waves) from the earthquake help triangulate the location of the epicenter by way of the Richter scale. The Richter scale, which is based on a logarithmic scale, measures the energy released by an earthquake; so, an earthquake measuring 4.0 on the Richter scale releases 10 times the energy as compared to one measuring 3.0.

It is estimated that there are on average 130,000 earthquakes worldwide measuring between 3.0 and 3.9 each year (USGS, 2011). The most powerful earthquake recorded was in Valdivia, Chile in 1960, measuring 9.5 on the Richter scale. It generated a tsunami that traveled over 10,000 km across the Pacific Ocean, striking Japan and the Philippines with waves as high as 35 feet.

Fig.8.png Description: Description: Description: GE.gif Expand the EARTHQUAKES folder, expand the 2011 Earthquakes folder, and check only USGS Logo and Legend (Figure 4).

Figure 4. Legend.

Within this folder are the locations, magnitudes (based on the Richter scale), and depths of all recorded earthquakes in 2011 (you might have to zoom in or zoom out to see the epicenters).

Description: Description: Description: Description: Description: GE.gif Doubleclick the Magnitude 9 folder.

Question 23: Where was the magnitude of 9 or higher recorded in 2011?

A. Off the coast of California

B. Off the coast of Chile

C. Off the coast of Japan

D. Off the coast of Hawaii

Description: Description: Description: Description: Description: GE.gif Uncheck the Magnitude 9 folder. Doubleclick and select the Magnitude 7 folder.

Question 24: How many earthquakes with a magnitude between 7 and 7.9 were recorded in 2011?

A. 19

B. 14

C. 26

D. 33

Question 25: How many earthquakes with a magnitude between 7 and 7.9 and a depth of 0-35 km were recorded in 2011?

A. 8

B. 10

C. 12

D. 15

Description: Description: Description: Description: Description: GE.gif Uncheck and then recheck the 2011 Earthquakes folder. Verify that all boxes are checked (from USGS Logo to Magnitude None).

Question 26: Based on a visual inspection of the globe, which country experienced the most earthquakes in 2011? (You might have to zoom in or out).

A. Japan

B. Chile

C. Russia

D. United States

Question 27: With respect to all earthquakes, most of them are located along the perimeter of the Pacific Ocean. What is this area - with its distinct pattern of earthquakes - known as?

A. Edge of fire

B. Ring of fire

C. Pacific tectonic zone

D. Ring of earthquakes

Description: Description: Description: Description: Description: Description: GE.gif With the 2011 Earthquakes selected, check the PLATE BOUNDARIES folder.

Question 28: Which of the following describes the spatial relationship between plate boundaries and earthquake epicenters.

A. They are seldom found near each other

B. They appear to be randomly distributed

C. They are often found together

D. There is no apparent spatial relationship

GE.gif Collapse and uncheck the EARTHQUAKES and PLATE BOUNDARIES folders.

HOTSPOTS

Description: GE.gif Expand the HOTSPOTS folder and then click Hotspot Animation to view an animation of this type of convergence boundary.

Description: GE.gif Doubleclick and select Seamount Chain and Kilauea.

Most scientists believe that the Hawaiian Islands and the associated Hawaiian-Emperor Seamount Chain were created by a hotspot. A hotspot is a stationary location in the asthenosphere where a magma plume upwells and forms a seamount (an undersea volcano). If tectonic activity is sufficient, the seamount will grow, break the surface of the ocean, and eventually form an island.

Although the hotspot remains stationary, the overlying plate continues to move, resulting in a series of islands, atolls (coral islands with lagoons), and seamounts that show the movement of the plate over millions of years. Within this chain, the plate movement is evident as you move away from the Big Island of Hawai’i where the hotspot currently exists. At the end of the seamount chain is Meiji Guyot, created about 82 million years ago and considered by many to be the oldest seamount in the chain.

As the bend in the chain suggests, the Pacific plate has not always move at the same rate or in the same direction. Researchers theorize that about 43 to 50 million years ago, the Pacific plate changed direction and shifted from a northerly direction to a more westerly one. Currently, the Pacific Plate is moving in a northwest direction. And while the hotspot is currently under Kilauea on the Big Island of Hawai’i, it is also forming Li’iho Seamount, a new seamount about 35 km southeast from the Big Island.

Description: Description: Description: GE.gif In the Table of Contents, open the Layers pane, and verify Borders and Labels is selected. You might have to zoom in to see the labels of the islands.

Question 29: Using the ruler tool, what is the distance in miles from Kilauea to the center of Kauai? _________

A. ~ 235 miles

B. ~ 325 miles

C. ~ 525 miles

D. ~ 352 miles

Kauai was formed about 5.1 million years ago.

Question 30: Using the information above, calculate the average rate of speed (in inches per year, or in/yr) of the plate since the creation of Kauai? (Remember: Convert miles to inches: 63,360 inches = 1 mile). Show your work.

A. 235 miles * 63360 inches/mile / 5,100,000 years = 2.92 inches/year

B. 352 miles * 63360 inches/mile / 5,100,000 years = 4.37 inches/year

C. 525 miles * 63360 inches/mile / 5,100,000 years = 6.52 inches/year

D. 325 miles * 63360 inches/mile / 5,100,000 years = 4.04 inches/year

Question 31: Using the ruler tool, what is the distance in miles from Kilauea to the center of Maui?

A. ~90 miles

B. ~110 miles

C. ~130 miles

D. ~150 miles

Maui was created about 1.3 million years ago.

Question 32: Using the information above, calculate the average rate of speed (in inches per year, or in/yr) of the plate since the creation of Maui? (Remember: Convert miles to inches). Show your work.

A. 90 miles * 63360 inches/mile / 1,300,000 years = 4.39 inches/year

B. 150 miles * 63360 inches/mile / 1,300,000 years = 2.63 inches/year

C. 130 miles * 63360 inches/mile / 1,300,000years = 3.04 inches/year

D. 110 miles * 63360 inches/mile / 1,300,000 years = 3.56 inches/year

Question 33: Do hotspots occur only in the ocean? Explain why or why not.

A. Yes, because they form only under oceanic crust

B. Yes, because there is no evidence of them under continental crust

C. No, because, there is evidence of them under continental crust (e.g. Yellowstone)

D. No, because the Andes Mountains in South America are a good example of a hotspot

Description: Description: Description: GE.gif In the Table of Contents, go to the Layers pane, and uncheck Borders and Labels.

GE.gif Collapse and uncheck the HOTSPOTS folder.

FAULT TYPES

Description: Description: Description: Description: GE.gif Expand the FAULT TYPES folder and then click Fault-Types Animation to view an animation.

Folding is the process by which rocks compress and deform. Several kinds of geologic structures are associated with this process, including anticlines, synclines, overturned fold, and overthrust faults.

Description: Description: Description: Description: GE.gif Double-click Fly-over: Appalachian Mountains.

Description: Description: Description: Description: GE.gif Close the animation control panel:

Description: Description: Description: Description: GE.gif Double-click and select Appalachian Mountains.

This area of the Appalachian Mountains is known as the Ridge and Valley Province. The geomorphology, or spatial form and evolution of the land, consists of many ridges and valleys. Anticlines form most of the ridges in this area, while synclines make up many valleys. However, over millions of years, an inversion can occur in which structurally, synclines become ridges and anticlines become valleys. This is due in part to the erosion of softer rock by water over time. A resultant landform in these structurally inverted landscapes consists of steeply sloped ridges with sharp summits known as hogback ridges, which occur on each side of an anticline valley.

Question 34: Is Feature H.gif an anticline or syncline?

A. Anticline

B. Syncline

C. Hogback ridge

D. Both a syncline and anticline

Question 35: What is Feature I.gif (linear feature) which is located at the base of the Rocky Mountains? ________________

A. Anticline

B. Syncline

C. Hogback ridge

D. Both a syncline and anticline

Description: Description: Description: Description: GE.gif Double-click and select Appalachian Mountains.

Many geographers recognize four major faults – normal (Figure 5), reverse (Figure 6), overthrust (Figure 7), and strike-slip (Figure 8) faults.

Figure 5. Normal Fault (Arbogast 2nd Ed.).

Figure 6. Reverse Fault (Arbogast 2nd Ed.).

Figure 7. Overthrust Fault (Arbogast 2nd Ed.).

Figure 8. Strike-Slip Fault (Arbogast 2nd Ed.).

In the following questions, answer and identify these types of faults. Where there is a series of normal faults, horst and graben can be found.

Question 36: What is the name of the cliff face formed by a normal fault?

A. Scarp

B. Talus

C. Scree

D. Slide

Question 37: What is Feature J.gif?:

A. Horst

B. Graben

C. Ridge

D. Reverse fault

Question 38: What is Feature K.gif?:

A. Horst

B. Graben

C. Ridge

D. Reverse fault

Question 39: What fault is not associated with uplift?

A. Normal

B. Reverse

C. Overthrust

D. Strike-slip

Question 40: Are faults limited to land, or can they occur under water as well? Explain why or why not.

A. Limited to land, as there is no evidence of faulting under water

B. Limited to land, as faulting is a continental crust phenomenon

C. Not limited to land, as faulting can occur under water

D. Not limited to land, as faulting requires at least one side to be oceanic.

References

USGS. 2011. http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php. Accessed December 15, 2011.