Introduction to the Seafloor
Original Source: Dr. Leslie Sautter (Dept. of Geology, College of Charleston)
Grade Level:
SC Standards:
5th & 8th Grade
National Standards:
Earth and Space Science – Content Standard D
5th – IIIA1a,b,d,f,g; IIIA2a,b,c
8th – IIIB1c,f,g; IIIB3b,c,j,k; IIIB4a,b,f
Focus Questions
What are the major types of seafloor
features?
Do these seafloor features show any
patterns and/or associations with each
other?
Objectives
Students will:
observe various features of the seafloor
depicted on a physiographic map of the
ocean floor.
identify ridges, trenches, seamounts,
volcanic island chains and fracture zones and
describe their large-scale characteristics.
examine the geographic associations
between features (i.e., those that are
parallel to one another and those that are
perpendicular to one another).
Key Words
ocean basins
arcuate and linear features
mid-ocean ridges
fracture zones
trenches
seamounts, seamount chains
volcanic islands, volcanic mountains
Materials
For each group of students:
photocopy of STUDENT PAGES.
physiographic map of the ocean floor. This
activity was developed using the TASA
Graphic Arts map. ($5 from Syzygy Arts,
Inc., http://www.syzygy06.com)
large sheet of tracing paper (if not
available, use plain paper)
pencil and eraser
4 color pencils
For the teacher:
physiographic map of the ocean floor, large
version of the same map, if possible
globe - inflatable works well (Note: the
globe needs to have a light colored ocean so
that the pen marks will show)
transparency marker pens, four different
colors (to write on the globe)
baseball or softball (optional)
Time Frame
One to two 50-minute class periods
Suggested Learning Environment
Students should work in cooperative groups of
3-4. With enough materials, this activity works
well for an entire classroom of students.
Relevant pages in “Of Sand and Sea
Chapter I, The Ocean Planet, pp. 1-6.
Teacher Preparation
Stress to students that this is an observational
activity, and that they are doing what
oceanographers did in the 1950s and 1960s as
they first began to have a "picture" of the
ocean floor. This activity is not intended to
teach students how these seafloor features
were formed. It is designed to be the first in a
series of three activities. “Introduction to the
Seafloor” should be followed by “Quakes and
Plates” and “The Puzzling Plates.”
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Introduction to the Seafloor
TEACHER PAGES
The teacher may lead the activity, by reading the
instructions on the STUDENT PAGES aloud, and
posing questions to the class as a guided inquiry.
Or, the teacher may wish the activity to be
student-led, providing STUDENT PAGES to each
student group.
Procedure
Students should follow the steps below, found on
the STUDENT PAGES, while taking notes in their
science notebook. Information for the teacher is
provided in blue italics.
It is very important to remind students that this
activity is not designed to teach the formation of
these seafloor features. It is to observe the
features and identify associations among the
different types of features. Encourage all students
to participate, and when they locate features ask
them point to the map and trace the features. This
ensures that all students in the group are finding
the designated features together. To protect maps
from being marked on, ask students not to use pens
or pencils to point out features on the map.
1. Name and locate all of the continents.
 North America, South America, Africa, Eurasia,
Australia, Antarctica
 Note that Europe and Asia are not separate
continents! Geologically, they are on the same
continental land mass, whereas politically they
are separate.
2. Identify linear (straight-line) and arcuate
(curved-line) features on the continents. Do not
include rivers or coastlines.
Throughout this activity the student is asked,
“What is the geographic association between ___
and ___?” Discuss with students that this type of
question is seeking an answer to identify patterns in
the seafloor features and if the patterns occur
several times. Try to get the students to use
geometric terms such as „parallel to‟ or
„perpendicular to.‟ A sentence describing the
association might be structured, “___ and ___ are
parallel to each other,” or “___ is perpendicular to
____.”
a.
Identify the major mountain chains and
trace them with your finger.
 Be certain to include the following: Andes
Mountains (S. America), Appalachian
Mountains and Rocky Mountains (N.
America), Himalayas (northern India), Ural
Mountains (Russia), and the Caledonian
Mountains (on the coast of Scandinavia).
b. Find linear lakes in Africa.
 These lakes comprise the East African Rift
Valley.
Students will conduct the activity by following the
steps listed in the STUDENT PAGES. The
procedure follows, and notes for the teacher are
bulleted (diamond-shaped bullet), in blue italics.
3. Move to the ocean. Name and locate the four
major ocean basins (major oceans).
 Pacific, Atlantic, Indian and Arctic Oceans.
Most maps do not show all of the Arctic Ocean.
 You may have heard of the Southern Ocean, but
that is not an ocean basin. Oceanographers
study the “Southern Ocean” because of the
currents and circulation that connects the
southern portions of the Pacific, Atlantic and
Indian Oceans.
Assessment questions are included for students to
answer in a science notebook or on separate pages
to hand in. Guidelines for evaluating student
answers are included.
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Introduction to the Seafloor
TEACHER PAGES
a.
offset from one another, along these
fracture zones.
Note that oceanographers often refer to
the North Atlantic and the South Atlantic
Oceans, even though they are both part of
one major ocean basin.
c.
 The Hawaiian Ridge is not broken into
b. Remember that the Earth has only one
interconnected ocean; however there are 4
major ocean basins.
numerous ridge segments which are offset
by fracture zones. It is a very linear ridge
and is quite different from the others
previously examined. It is made of the
chain of seamounts and volcanic islands (to
be observed in the next section).
4. Locate the following seas and gulfs:
o Atlantic Ocean: Mediterranean Sea,
Caribbean, Norwegian Sea, Gulf of
Mexico
o Indian Ocean: Red Sea, and Arabian Sea
o Pacific Ocean: Gulf of California
a.
d. Find the Ninety East Ridge in the Indian
Ocean. Is it more like a mid-ocean ridge or
the Hawaiian Ridge?
 The Ninety East Ridge is not broken into
Note the linear nature of the Red Sea and
the Gulf of California.
numerous ridge segments and is more like
the Hawaiian Ridge.
5. Identify a variety of linear and arcuate
features on the ocean floor. List the different
types of features in your science notebook (or
on the chalkboard), and include several examples
of each type.
 Locate examples of ridges, trenches, volcanic
7. Trace the mid-ocean ridges with your finger,
beginning at Iceland in the North Atlantic
Ocean. See how far around the globe you can
“travel” just by traveling along mid-ocean ridges.
a. Compare this system of connected ridges to
the seam of a baseball. (See if your teacher
has a baseball to view.)
island chains, seamount chains, fracture zones,
etc.
6. Find Iceland. It sits on top of the Mid-Atlantic
Ridge, a classic mid-ocean ridge. Mid-ocean
ridges are underwater mountain chains. A rise
is another term for a ridge.
a.
Find the Hawaiian Ridge. How does it differ
from mid-ocean ridges?
8. Examine the Pacific Ocean and locate several
fracture zones. Find the following fracture
zones:
o Pacific Ocean: Eltanin, Challenger
o Atlantic Ocean: Gibbes, Romanche,
Rio Grande
o Indian Ocean: Owen, Prince Edward
Find several other mid-ocean ridges.
o Pacific Ocean: East Pacific Rise and
Juan de Fuca Ridge
o Indian Ocean: Southwest Ridge,
Southeast Indian Ridges and Carlsberg
Ridge
9. What is the geographic association between
ridges and fracture zones?
 Fracture zones are typically perpendicular to
ridge segments. Ridge segments are offset
from one another, with fracture zones between
them.
b. What other type of seafloor feature is also
found along mid-ocean ridges?
 Fracture zones are associated with mid-
ocean ridges. The ridge segments are
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10. (Optional) Using two different colors of
transparency (erasable!) marker pens, draw the
approximate locations of ridges and a few of
the largest fracture zones on a globe.
 If you cannot write on the only globe available,
Seamounts are volcanoes that originate on the
seafloor (not on a continent). Some have grown
so that they are above sea level, so we refer to
them as volcanic islands, while others are below
sea level and are called seamounts.
then use masking tape to mark the mid-ocean
ridges. Discuss the fracture zone locations.
a.
11. Find several ocean floor trenches. As you
locate each, trace them with your finger.
a.
Locate the following trenches:
o Pacific Ocean: Aleutian Trench,
Kuril Trench, Japan Trench,
Mariana Trench, Philippine Trench,
Tonga Trench, Peru-Chile Trench, and
the Middle America Trench.
o Atlantic Ocean: Puerto Rico Trench,
Cayman Trench, South Sandwich Trench
o Indian Ocean: Java Trench
 Note that Japan is comprised of a few
volcanic islands (seamounts that have grown
above sea level). These volcanoes have
merged to form one large island.
14. What is the geographic association between
trenches and seamount (or volcanic island)
chains?
 All of the seamount chains listed have a strong
b. The Mariana Trench is the deepest spot on
Earth at approximately 11 km (6.8 miles)!
The Mariana Trench is deeper than the
entire height (relief) of Mount Everest!
c.
Locate the following volcanic island chains
and trace them on your map with your
finger:
o Pacific Ocean: Aleutian Islands, the
Kuril Islands (southwest of the
Kamchatka Peninsula), Japan, and the
Philippine Islands.
parallel association with trenches. There are,
however, other seamount chains that have no
trench nearby.
 Nearly all trenches have seamount chains
parallel to them.
Note that there is no trench off the
California coast, but there is a small trench
(the Juan de Fuca Trench) off the coast of
Oregon and Washington states.
15. Locate the following volcanic mountain chains
(on the continents):
o Andes Mountains, Sierra Madre (Central
American), and the Cascade Mountains (in
Oregon and Washington).
12. (Optional) Using a third color of transparency
marker pen, draw the location of trenches on
the globe.
 Again, you may want to use masking tape if you
16. What is the association between volcanic
mountain chains and trenches?
 All these volcanic mountain chains are
are unable to write on the available globe. Use a
permanent marker to color the masking tape
once it‟s on the globe, to distinguish trenches
from mid-ocean ridges.
associated with a nearby trench that is parallel
to them.
17. (Optional) Using a fourth color of transparency
marker pen, draw the location of seamount
chains on the globe.
13. Examine the Pacific Ocean again to find
seamounts that are arranged in chains.
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TEACHER PAGES
 Again, you may want to use masking tape if you
are unable to write on the available globe.
e.
18. Find the Hawaiian Islands. These islands are
part of a long chain of seamounts that extends
northwest, beyond the islands. Beginning at the
big island of Hawaii, trace your finger along the
chain. In what direction is your finger moving?
What is the ridge called?
a.
 These seamounts are confusing, so they
need to make statements such as the
following:
1) Most (if not all) trenches have an
associated seamount/volcanic island chain or
continental volcanic mountain chain parallel
to them. Examples: Aleutian Trench and the
Aleutian Islands; Peru-Chile Trench and the
Andes Mountains
2) Some seamount/volcanic island chains
have no trenches associated with them.
Example: Hawaiian Island Ridge seamount
chain.
3) Some seamount/volcanic island chains are
associated with fracture zones – they are
aligned with these fracture zones. Example:
Louisville Ridge seamount chain and the
Eltanin Fracture Zone.
Is this the same kind of ridge as a midocean ridge?
 No, it is different. It does not have
fracture zones.
b. What occurs to the volcanic chain at
approximately 170°E longitude? What is
this feature called?
 The seamount chain bends northward. This
is called the Emperor Seamount Chain.
c.
Summarize your observations about
seamount chains, volcanic island chains,
volcanic mountain chains, trenches and
fracture zones. Provide an example for
each observation.
Are there any trenches associated with
either of these two seamount chains? Is
the association similar to other seamount
chains and trenches?
 There are no trenches parallel to either of
19. Now that you have explored the various types
of seafloor features throughout three of the
four major ocean basins, let‟s take a seafloor
tour around the Pacific Ocean. Begin off the
coast of Alaska, at the eastern end of the
Aleutian Trench. What arcuate feature is just
north of this trench?
 The Aleutian Islands are north of the trench.
these seamount chains; however, students
may observe that the Aleutian Trench is
perpendicular to the Emperor Seamount
Chain. If this observation is made, ask if
they can find any other seamounts that are
perpendicular to trenches. They are unlikely
to find them.
d. Find the arcuate Louisville Ridge, northeast
of New Zealand and trace its orientation
from west to east. If you continue to move
your finger in the same general arcuate
eastward direction, what seafloor feature
do you encounter that is also oriented
similarly?
 This seamount chain has no trench
a.
With your finger, follow the Aleutian
Trench westward until other linear or
arcuate features are encountered. Trace
the trenches all the way to New Zealand.
b. What are the trenches you encountered
along the way? Were there any other
seafloor features associated with those
trenches?
associated with it, but is along the same
arcuate line as the Eltanin Fracture zone.
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 There are many trenches that interconnect
c.
American continent at the northern tip of
the Gulf of California.
along this path. Students may choose a path
that includes either the Philippine Trench or
the Mariana Trench. There are volcanic
islands all along this path.
20. At this point, you‟ve traveled nearly the entire
perimeter of the Pacific Ocean basin by hopping
from one seafloor feature to another.
But you aren‟t finished yet… (we just need to
take a quick detour across California).
As you head generally eastward from the
Philippine region, you will find many broken
segments of trenches, and a lot of volcanic
islands.
a.
d. What is the name of the linear trench north
of New Zealand?
 This is the Tonga Trench.
e.
From New Zealand, travel south until you
encounter the East Pacific Rise (EPR).
Follow this mid-ocean ridge system
eastward until you find a seafloor feature to
follow that takes you to the edge of South
America. What feature did you find?
 Students may find the Chilean Ridge, the
Nazca Ridge or the Galapagos Ridge. Each
of these ridges branches off of the EPR and
runs eastward, ending at the South
American coast (or at the Peru-Chile
Trench).
f.
b. It will be difficult to find a seafloor feature
to connect the northern end of the Juan de
Fuca Ridge to your starting point at the
Aleutian Trench. So your tour has ended,
but you have almost completed a circumPacific journey!
What feature can you now follow all along
the coast of South America towards Central
America?
21. Now you have completed your tour of the Pacific
Ocean. On a separate piece of paper (or, using
tracing paper) draw a map of the path you've
just traveled, labeling the major features along
the route. Use the following symbols to identify
different seafloor features:
 The Peru-Chile Trench is parallel to the
coast of South America.
g.
From the northern end of the Gulf of
California, move across southern California,
past Los Angeles to San Francisco, then
northward to the small Juan de Fuca Ridge
off the coast of Oregon and Washington.
This path is the trace of the San Andreas
Fault. It is neither a ridge nor trench, but
is actually a fracture zone that connects
two ridge segments (the Gulf of California
segment and the Juan de Fuca Ridge
segment).
What seafloor feature do you encounter
parallel to the coast of Central America?
 The Middle America Trench is parallel to
the Central American coast.
h. As you move toward North America, you will
reconnect to the EPR as it zig-zags into the
Gulf of California. The Gulf of California is
a very linear sliver of ocean between Mexico
and the very linear Baja Peninsula. The EPR
appears to end as it runs into the North
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22. Now let‟s examine the Atlantic Ocean. Would
you be able to take a similar circum-Atlantic
tour following seafloor features?
 No, there are very few trenches in the Atlantic
23. Make a chart that compares the abundance of
trenches, mid-ocean ridges, fracture zones,
volcanic island chains, and volcanic mountain
chains of the Pacific and Atlantic Ocean basins.
Ocean and, unlike the Pacific Ocean they do not
rim the basin.
a.
24. Review the associations you‟ve observed among
ridges, trenches, volcanic island chains,
seamount chains and continental volcanic
mountain chains.
Can you find seamount chains similar to the
Hawaii, Nazca and Louisville Ridges of the
Pacific Ocean?
 Yes, but there are not nearly as many and
25. Continue with your exploration by doing the
activity “Quakes and Plates” followed by
“The Puzzling Plates.”
they are fairly short. The Walvis Ridge (off
of Africa) and the Azores Islands are both
chains of seamounts and volcanic islands.
There are also short volcanic island chains
associated with the few trenches that exist
in the Atlantic.
Summarize your observations and discoveries by
answering the questions on the next page.
Questions (Assessment)
Use your observations of the seafloor features and the associations between and among these features to
answer the following questions. Your teacher will provide information of how to format your answers.
1) What are the associations between or among the following seafloor features and continental feature?
Describe the characteristics observed (including if the features exhibit linear and/or arcuate
geometries) and, generally where they are found in each ocean. For each feature include any associated
seafloor features and their geographic relationship. Expand your observations from step number 18e.
For each association, provide and example.
Mid-ocean ridges
Fracture zones
Trenches
Volcanic island chains/seamount chains
Volcanic mountain chains
 Mid-ocean ridges have linear segments that are offset by linear or arcuate fracture zones. They are
found in the mid-Atlantic and in the southeastern portion of the Pacific. There are 3 branches of a
mid-ocean ridge in the Indian Ocean. There is also a ridge that runs across the Arctic Ocean
(though it is not evident on most seafloor maps).
Atlantic Ocean Example: Mid-Atlantic Ridge and Romanche Fracture Zone or Gibbes Fracture
Zone
Pacific Ocean Example: East Pacific Rise and Eltanin Fracture Zone
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Indian Ocean Example: Mid-Indian Ridge and the Owen Fracture Zone
 Fracture zones are the linear or arcuate features that lie in between the offset ridge segments
(examples are above). Some of these fracture zones are parallel to or aligned with seamount chains.
Pacific Ocean Example: Eltanin Fracture Zone and the Louisville Ridge
 Trenches are the linear or arcuate features found mostly in the Pacific, and occur all along the
northern and western edge of the Pacific Ocean Basin. There are fewer in the other 3 ocean basins.
Trenches are almost always found parallel to a chain of volcanoes. These volcanoes may be
seamounts or volcanic islands, or they may be continental volcanoes.
Pacific Ocean Example with volcanic islands: Aleutian Trench and the Aleutian Islands; Kuril
Trench and Kuril Islands; Philippine Trench and Philippine Islands
Atlantic Ocean Example with volcanic islands: Puerto Rico Trench and Puerto Rico
Pacific Ocean Example with continental volcanoes: Peru-Chile Trench and the Andes Mountains;
Juan de Fuca Trench and the Cascade Mountains
2) How is the Hawaiian Ridge different from the East Pacific Rise? Identify a ridge in the Indian Ocean
that is similar to the Hawaiian Ridge. How is this ridge similar to or dissimilar to the Hawaiian Ridge?
 The Hawaiian Ridge is a chain of seamounts and volcanic islands. It is not a series of linear ridge
segments that are offset by fracture zones. The Ninety East Ridge in the Indian Ocean is similar to
the Hawaiian Ridge, although it doesn‟t have the distinct, individual seamounts.
3) Find a sea or gulf that is similar to the Gulf of California. Explain how these two locations are similar.
 The Red Sea is narrow and linear, similar to the Gulf of California. Both of these seas have a small
mid-ocean ridge in the middle of them.
4) If you were to travel north from Iceland along the Mid-Atlantic Ridge where do you think it would take
you?
 The Mid-Atlantic Ridge would lead me north up and over the north pole (or close to it!), into and
across the Arctic Ocean.
5) Where is the world‟s longest chain of trenches that have volcanic islands or seamounts?
 The longest chain of trenches in the world is in the northern and western Pacific Ocean basin. It
begins with the Aleutian Trench and ends with the Philippine Trench (or the Mariana Trench,
depending on the path you take).
Source: Dr. Leslie Sautter, Project Oceanica, Dept. of Geology and Environmental Geosciences, College of Charleston, SC.
website: http://oceanica.cofc.edu email: [email protected] phone: 843-953-5586
Funding for the COASTeam Program was provided by the South Carolina Sea Grant Consortium. http://oceanica.cofc.edu/coasteam/
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