Purpose:
 To locate topographic features on the ocean floor.
 To study the relationships that exist between and among the plotted features and the continents.
Procedures:
 Using the outline map of the world and the National Geographic Map provided by your
instructor, locate the places that are in the data table below.
 Label those places with the appropriate number.
 Lightly shade the island arcs (chains of volcanic islands) in green.
Lightly shade the volcanic arcs (chains of volcanic mountains) in green too
 Indicate the Hot Spots with a big yellow circle with an X in it..
 Lightly shade the trenches/subduction zones in red
 Lightly shade the ocean ridges/rises in blue.
 Fractures/faults should be indicated with a black line.
 When you have completed your map, answer the questions that follow on a separate sheet of
paper.
Locate the following:
Pacific Ocean Features
Pacific Ocean Features
Atlantic Ocean
Features
1.
18. Island of Hawaii (yellow)
(Central Pacific Ocean)
19. Emperor Seamounts and
Hawaiian Ridge (yellow line)
(NW Pacific, between Hawaii
and Aleutian Trench)
20. Middle America Trench (SW of
Mexico)
21. Mexico/Central America
Volcanic Arc
22. Cocos Ridge (East Pacific, off
NW South American Coast)
23. Galapagos Island (Northern
South America)(yellow)
27. Mid-Atlantic Ridge and
Reykjanes Ridge (just
South of Iceland) – all part
of Mid-Atlantic Ridge
28. Iceland -label in yellow(North Atlantic)
29. Puerto Rico Trench (South
of US)
30. Caribbean Island Arc
31. Romanche Fracture Zone
(Central Coast of Africa)
32. Azores -label in yellow(West of Europe)
33. South Sandwich Island Arc
(South of South tip of
Africa)
34. South Sandwich Trench
(South of South tip of
Africa)
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13
14.
15.
16.
17.
East Pacific Rise -Ridge- (off west coast of South
America)
San Andreas Fault/fracture (California, US)
Gorda Ridge (off OR coast- check back side of
map)
Juan de Fuca Ridge (off OR coast- check back
side of map)
Cascadia Subduction Zone –Trench- (off OR
coast-check back of map)
Cascade Mountains (volcanic arc)
Aleutian Trench (N. Pacific- Alaska)
Aleutian Island Arc (N. Pacific – Alaska)
Kuril, Japan, and Kryukyu Trenches (West
pacific -Japan)
Japan Island Arc (E. Pacific)
Peru-Chile Trench (W. Coast of South America)
Andes Mountains (W. coast of S. America)
Mariana Trench (W.est Pacific, South of Japan)
Philippine Trench (W. Pacific, East of
Philippines)
Philippine Island Arc (W. Pacific)
Pacific Antarctic Ridge (South Pacific, North of
Antarctica)
Cobb Seamount (yellow) (Off Oregon Coast)
Indian Ocean
Features
24.
25.
26.
27.
Mid-Indian Ridge
Southeast Indian Ridge
Southwest Indian Ridge
Java Trench (Southern
Indonesia, between Australia
and Indonesia)
28. Islands of Sumatra and Java
Ridge (not a ridge, but an island
arc) (Southern Indonesia,
between Australia and
Indonesia)
Others:
35. East African Rift System
(orange)
Questions:
1.
Generally speaking, where are the ridges/rise (diverging plates boundaries) located with respect to the
continental landmasses?
2.
What is the one exception? (hint you didn’t label it in blue like all the other diverging boundaries)
3.
Examine your map. Does there appear to be any relationship (spatial) between the location of island arcs
(Aleutian Islands, Japan Islands, Tonga Islands, Philippine Islands) and the oceanic trenches? Explain. Make sure
to address arc / trench location relative to plate movement.
4.
Where do you find volcanic mountain ranges (Northwestern US’s Cascades, South American’s Andes) with
respect to the trenches? Make sure to volcanic arc / trench location relative to plate movement.
5.
What are seamounts? (Check your textbook on page 520)
6.
How was the Cobb Seamount in the NE Pacific Ocean formed? (Check map legend)
7.
Follow the Hawaiian Islands Northwest and you’ll see a line of seamounts. These seem to bend to the right at
some point (about where the “N” is in North Pacific. What direction do the seamounts now head? What is the name of
these seamounts?
8.
Most of the Pacific Ocean is on what plate?
9.
What is the compass orientation of the Hawaiian Islands and many of the other smaller ridges within the Pacific
Ocean? Is this significant?
10. What compass direction is the Pacific Plate moving?
11. Examine the East Pacific Rise. Faults along the mid-ocean ridges indicate movement perpendicular to the ridge, not
just parallel. Is the movement away from the ridges uniform all along the ridge? In other words, do all parts of the ridge
spread at the same rate?
12. Examine your map, name the biggest and longest mountain range in the world (in the water or on land).
13. Name an island chain that has been formed by a "hot spot", other than Hawaii.
14. What island in the north Atlantic Ocean is splitting apart? What caused the split?
15. The Juan de Fuca Plate and the Gorda Plate were once one big plate called the _???????????_plate. This big plate
existed how many million years ago? (Check other side of map in the lower left corner)
16. What feature is formed where magma is rising to the surface and forming new ocean crust?
17. What feature are formed where oceanic crust is sinking back (subducting) into the mantle?
18. Some people have referred to the processes in #16,17 as a cycle. Why would they be considered a cycle?
19. Why is it that the Pacific Ocean floor is no older than about 200 million years and yet the continents are much older
(billions of years old)?
20. The edges of the continents on the East and West Coast of the United States are very different. Describe the differences.
Are there any tectonic differences (boundaries present)?
21. Examine South America. Where is the land rugged versus where is it flat? What relationship exists between
ruggedness and plate boundaries?
22. Why are Australia and Africa rather flat compared to other continents?
Part V THE EARTH'S FRACTURED SURFACE
KEY
Questions: (Answer on a separate piece of paper)
1. Generally speaking, where are the oceanic ridges located with respect to the landmasses?
They often run parallel to the continents
2. Examine your map. Does there appear to be any relationship between the location of island
arcs (Aleutian Islands, Japan Islands, Tonga Islands, Philippine Islands) and the oceanic
trenches? Explain.
The island arcs are usually on the continental side of the trenches.
4. Where do you find the mountain ranges with respect to the trenches?
Use examples.
Parallel to them and on the edges of the continents.
4. Are there any places on earth where the mid-ocean ridges meet the continent?
Yes. The San Andreas Fault is the extension of the East Pacific Rise.
5. What are seamounts?
Underwater mountains. If they are flat-topped they are called guyots.
6. What is special about the Cobb Seamount?
It is off the coast of Washington and represents a volcanic mountain (part of a chain of
mountains) whose origin was on the Juan de Fuca Ridge.
7. What is the relationship between the Emperor Seamounts and the Hawaiian Islands?
If you followed the Hawaiian Islands to the NW you would eventually meet the Emperor
Seamounts. It is possible that the Emperor Seamounts were once volcanic islands like the
Hawaiian Islands.
8. Most of the Pacific Ocean is on what plate?
The Pacific Plate
9. What is the compass orientation of the Hawaiian Islands and many of the other smaller ridges
within the Pacific Ocean? Is this significant?
A northwest orientation. Perhaps they all reflect the Pacific Plate movement which trends
NW.
10.What compass direction is the Pacific Plate moving?
Toward the NW.
11.What kind of fault does the Mendocino Fracture Zone represent?
A transform fault.
12.On either side of the East Pacific Rise are some smaller faults. What does this suggest about the
activity at the East Pacific Rise?
It is moving. Stretching. The faults represent stretch marks.
13.Transform faults along the mid-ocean ridges indicate movement perpendicular to the ridge. Is
the movement away from the ridges uniform all along the ridge?
No. The spreading rates vary and the lengths of the faults vary.
14.Name the biggest and longest mountain range in the world. How long is it?
MidOcean Ridge. It is about 40,000 km (25,000 miles) long
15.Name an island chain that has been formed by a "hot spot". Checking the web sites might be
very helpful.
The Hawaiian Islands
16.What island in the north Atlantic Ocean is splitting apart? What cause the split? Iceland. It
straddles the Mid-Atlantic Ridge which is a
place where two plates are diverging (moving apart).
17.Why are there many more abyssal plains in the Atlantic Ocean compared to the Pacific Ocean?
Tectonically less active region and also more sediments are deposited in the Atlantic.
18.The Juan de Fuca Plate and the Gorda Plate were once one big plate called the _xxxxx_plate.
This big plate existed how many million years ago?
Farallon Plate. 30-50 million years ago.
19.Where is magma rising to the surface and forming ocean crust and where is the oceanic crust
sinking back into the mantle?
Mid-Ocean Ridges Trenches
20.Some people have referred to the process in the above question as a cycle. Why would it be
considered a cycle?
Magma is born at the ridges and destroyed at the trenches.
21.Why is the Pacific ocean floor no older than about 200 million years and yet the continents are
much older?
The Pacific Plate is subducted so no oceanic rock is older than 200 million years while the
continents are not subducted so they just age.
22.What are the attributes of a cycle? Can you name another cycle?
Rock Cycle, Water Cycle, Stellar Cycles
23.What features are found at plate boundaries?
Mountains, Faults, Rift Valleys, Trenches
24. Notable earthquakes are listed and mapped. How does an earthquake get on the notable
earthquake list?
Having a high magnitude and/or many deaths
25.Are there any earthquakes on the notable list that occurred inland from continental margins?
If there are notable earthquakes inland, where are they?
Yes. China, Bolivia
26.The continental margins of the East and West Coast of the United States are very different.
Describe the differences. Are there any tectonic differences?
The East Coast has a wide continental shelf while the West Coast has a narrow
continental shelf. The tectonically active areas have narrow shelves associated with
trenches faults and regional uplift.
27.As the Juan de Fuca Plate subducts, it brings down with it some sediments and water. What
might be the significance of the *water in the subduction process?
Lowers the melting point of the mantle rock.
Extensions:
 How does water effect the melting point of a subducting plate of basalt as it enters the mantle?
This can best be answered by looking at the USGS web site on Plate Tectonics.
A phase diagram indicating temperature with depth in the mantle with and without
water could be graphed.
Water plays fundamental roles in many of the tectonic processes of the solid Earth.
Seismicity and volcanism on Earth would be very different in the absence of liquid water.
For example, the presence of groundwater in rocks greatly reduces their strength, making
them more likely to fail. In subduction zones, the water carried into the mantle by the
down-going oceanic plate significantly changes the melting temperature of mantle rock
and gives rise to explosive volcanic activity at converging plate boundaries.
 Draw the Rock Cycle and relate it to the Plate Tectonic Cycle.
The internet and textbooks usually contain rock cycles.
 Research the evolution of the Appalachian Mountains and the Rocky Mountains.
Check the Internet
 It has been said that we can "see" within the Earth using acoustic tomography.
Look up the word. Do you think it is possible to "see" old plate subduction sites on continents?
Yes, see the example below.
 It is difficult to
walk the
outcrop when
you are at the
bottom of the
sea. On
continents,
however, there
are
opportunities
to study the
sea floor. The
ocean floor has
its inland
analogs. Look
up the word
ophiolite in the library or on the Internet. Give an example of an ocean floor structure that has an
analog on the continent.