Download Lab #2 – Interpreting Tectonic and Bathymetric Maps

Geology 2 – Physical Geology Lab
Lab #2 – Interpreting Tectonic and Bathymetric Maps
Student Outcomes:
 Be able to understand and use basic map information, including scale, contour interval, legend, etc.
 Be able to recognize tectonic features, including mid-oceanic ridges, seamounts, trenches, and plate
boundaries on a bathymetric map
 Be able to identify the three types of tectonic plate boundaries using a bathymetric map
 Understand the processes occurring at the three types of plate boundaries
 Be able to determine the direction of tectonic plate motion by interpreting seafloor features on a bathymetric
map
 Create a cross-section using a bathymetric map
 Understand and use contour lines and contour intervals on a map
 Recognize and identify topographic features associated with the San Andreas and San Gregorio Faults
 Be able to identify seafloor features such as continental shelf, continental slope, continental rise, submarine
canyons, and seamounts on a bathymetric map.
 Develop a beginning understanding of how our world works so the student can make more accurate
assessments of presented information about our world and become responsible leaders and voters.
Materials:
 Map of “Measured and Estimated Seafloor Topography” from World Data Center (Note: This map is on
reserve at the MPC library and at the class website)
 Map of “Monterey Bay National Marine Sanctuary” from Monterey Bay Sanctuary Foundation, 1999.
 Wall map of the World
 Various other bathymetric maps and resources available during lab
 Plate tectonic map of the world
 Globe
Bathymetry Map Orientation
1) Using the bathymetric map “Measured and Estimated Seafloor Topography,” locate the colored depth scale
at the top. What color represents the deepest areas of the ocean?
Lightest purple
2) What depth is represented by green? (Hint: Interpolate to the nearest 500 meters)
3500 m
3) What is the average depth of the oceans abyssal plains?
5500 to 6000 m
4) How would you distinguish ocean floor that is 6,000 meters deep from ocean floor that is 7,000 meters
deep?
6000 m deep is dark purple; 7000 m deep is light purple
Atlantic Ocean
1) Using the world wall map or other lab resources, name at least one place where the Mid-Atlantic Ridge is
exposed above sea level.
Iceland; Azores
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Geo 2 – Physical Geology Lab
Interpreting Tectonic and Bathymetric Maps
2) Using the bathymetric map “Measured and Estimated Seafloor Topography” locate the deep, broad abyssal
plains of the Atlantic Ocean. Where are there deeper areas of the Atlantic Ocean? (Hint: Remember the
deepest bathymetry is shown by a light purple color, not deep purple or blue.) Name or indicate the latitude
(using the scale on the right and left margins of the map) at least one of two clearly visible locations. What
is the tectonic setting of these deepest areas?
Deep-sea trenches where subduction of oceanic crust occurs. Scotia Trench near 60º S is 6000 to 7000 m
deep; Caribbean Trench is another location.
3) Is the east coast of South America at a plate boundary or in the middle of a plate? How do you know?
It is in the middle of the plate because there is not mid-ocean ridge or trench, nor any evidence of rifting or
transform faulting along the east coast of South America.
4) How does the shape of the Mid-Atlantic Ridge compare to the shape of the continental margins on either
side of the Atlantic Ocean? Why do you think this shape relationship exists?
The shape of the continental margins on either side of the Atlantic Ocean mimics the shape of the MidAtlantic Ridge. The shape of the ridge is preserved along the continental margins reflecting the original
splitting apart of the land mass at the Mid-Atlantic Ridge. Africa and South America continue to move
away from each other as sea floor spreading continues along the Mid-Atlantic Ridge.
Indian Ocean
1) Is Madagascar part of the African Plate? Why or why not?
Yes. Only shallow water separates Madagascar from the African continent, and there is no evidence of a
plate boundary (i.e., trench, mid-ocean ridge, transform features) between them.
2) Is Madagascar part of the African continent? Why? Or why not?
No. Deep water separates Madagascar from the African continent..
3) India and Australia are both part of the Indian Plate. Examining the portion of this plate northwest of
Australia, what features are found along the northeast boundary of the Indian Plate? What kind of tectonic
boundary is this?
Trench – a convergent boundary and a subduction zone where the Indian Plate is subducting under the
Eurasia Plate.
4) What features are found along the southwest boundary of the Indian Plate? What kind of tectonic boundary
is this?
Mid-oceanic ridge is a divergent plate boundary.
5) Considering your observations in answering the previous two questions, what direction do you think the
Indian plate moving? Explain your conclusion.
Indian Plate is moving northeast – oceanic crust forms at mid-ocean ridge along SW boundary and is
subducted in the trench located in the northeastern margin of the plate.
Pacific Ocean
1) What features do you find along the western boundaries of the Pacific Plate? What type of tectonic
boundary is this?
Deep-sea trenches along a subduction zone, a type of convergent plate boundary.
2) What features do you find along the southeastern boundary of the Pacific Plate? What type of tectonic
boundary is this?
Mid-ocean ridge, which is a divergent plate boundary.
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Geo 2 – Physical Geology Lab
Interpreting Tectonic and Bathymetric Maps
3) Considering your observations in answering the previous two questions, what direction do you think the
Pacific Plate is moving?
The Pacific Plate is moving northwest as new oceanic crust is formed by the mid-ocean ridge in the SE and
crust is subducted in the trenches along the western boundaries of the plate.
4) Locate the Hawaiian-Emperor Seamount Chain. Notice the bend in the chain. How might this bend have
formed? The age of the rocks at the bend is 43 million years old. Why do you think the seamounts become
progressively deeper to the north and west of Hawaii?
A change in the direction of the Pacific Plate movement. Seamounts become denser as they cool, causing
them to subside. The older seamounts are progressively deeper the farther away from the source hotspot.
5) Where in the Pacific Ocean would you expect to find the oldest oceanic crust? Why?
At a subduction zone farthest away from the mid-ocean ridge where the new crust is being formed.
6) Locate the Marshall Islands and the Louisville Ridge in the southwest Pacific on the map at the end of the
lab worksheet. Notice how the islands and the ridge seem to connect with one another. What do you think
happened to the missing islands in between? What feature do you see on the bathymetric map that supports
your guess?
The missing islands were subducted. The trench along here supports this idea.
7) Notice the chain of islands extending north from New Zealand. Why might you expect to find active
volcanoes on these islands? What kind of volcanoes would you expect them to be? Explain using what you
know about plate boundaries.
Active volcanism is characteristic of subduction zones and deep-sea trenches. Volcanoes would be
explosive -- strato-volcanoes with steep sides.
8) Using the bathymetric map, find the mid-ocean ridge in the southern Pacific Ocean at about 60 degrees
south. Notice how the mid-ocean ridge is composed of many offset sections. What type of plate motion
occurs in the linear areas between the offset ridges that are perpendicular to the ridges? (Hint: Consider the
plate motion that you know occurs at the mid-ocean ridges.)
Transform or left lateral strike-slip motion
Cross-sections
Using the bathymetric and topographic maps in lab, draw cross-sections along the lines indicated on the map at
the end of the worksheet. Use the lines A-B, C-D, and E-F provided on the next page to draw your crosssections. (Note that cross-section C-D goes right through Hawaii.) In your cross-sections, be sure to include
and label the following features, if present:
 Lithosphere
 Hot spots
 Asthenosphere
 Trenches
 Crust
 Convergent margins
 Approximate topography and bathymetry
 Divergent margins
 Sea level
 Transform margins
 Sites of active volcanism
 Mid-ocean ridges
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Monterey Bay Area
Refer to the map of the Monterey Bay National Marine Sanctuary put out by the Monterey Bay Sanctuary
Foundation (1999) to answer the questions in this section.
1) Find the San Andreas Fault (SAF) on the map.
a. In the northernmost part of the map, which bay marks the course of the SAF?
Tamales Bay and Bolinas Lagoon
b. Near what famous landmark is the SAF located offshore rather than onshore?
Golden Gate Bridge
c. Near what highway does the SAF cross the Pajaro River near Watsonville?
Hwy 101 or the unlabeled Hwy 129 from Watsonville
d. In the southern portion of the map, which highway follows the SAF most closely?
Hwy 25
e. What two topographic features can one recognize that identify the location of the SAF on this map?
Long linear valleys and linear ridges
f. What kind of fault is the San Andreas Fault?
Transform or right-lateral strike-slip
2) Note the light blue lines labeled with numbers in the offshore portion of the map. These lines are called
contour lines. A contour line is a line joining points of equal elevation, or, in this case, of equal depth. The
contour interval is the vertical distance between contour lines.
a. Referring to the map legend, in what unit is the depth recorded on this map?
meters
b. What is the contour interval on this map close to shore?
20 m
c. What is the contour interval on this map far from shore?
200 m
3) The Monterey Bay National Marine Sanctuary map shows several seafloor features exceptionally well,
including examples of the continental shelf, continental slope, continental rise, submarine canyons, and
seamounts. Locate and observe examples of each of these features on the map in lab.
4) Find the Monterey Fan in the southwestern region of the map. What type of material would you expect to
find here? How would it have gotten there? What could be the source?
We would expect fine-grained material (clay and silt particles) to have been transported through the
Monterey submarine Canyon and deposited on the Monterey Fan. The source is erosion from the land and
transported by rivers to the mouth of the Monterey Canyon.
5) How deep is the Monterey Canyon near the intersection with the Carmel Canyon in meters and in feet?
(One meter = 3.28 feet)
2000 m = 6560 feet
6) Find the reference map that shows the trace of the San Gregorio Fault south of San Francisco to the Santa
Lucia Range. Trace the San Gregorio Fault on the map in you lab handout. Using the Marine Sanctuary
map, describe two topographic features that are associated with the trace of the San Gregorio Fault.
The linear ridge north of Half Moon Bay and the Carmel Canyon off-shore
Congratulations on completing the Interpreting Tectonic and Bathymetric Map Lab! Remember the
bathymetric and the Marine Sanctuary maps are available for your use at the reserve desk at the library.
The bathymetric map is also available on the class website.
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Geo 2 – Physical Geology Lab
Interpreting Tectonic and Bathymetric Maps
Figures for Lab Worksheet
Pacific Ocean – questions 6 and 7
Cross-Sections Map
MPC/Geo2/Labs/Lab #2 - Interpreting Tectonic and Bathymetric Maps.doc/LTS
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