GEL 1 Discussio
n
Section
Explorin
g the Seafloor
Goal: To visualize bathymetric features of
the ocean basins so that
their tecto
nic
significance is more easily understood.
Introduction:
Seventy percent of the surface area of Earth is concealed from view beneath
the world’s oceans.
Most tectonic plate boundaries occur on the seafloor and are thus a
challenge to recognize. Methods of mapping the seafloor include sophisticated updates of
ech
o-sounding combined with massive computer firepower, and satellite measurements
of variations in sea level due to differences in the gravitational pull of the solid crust
beneath the oceans.
Google Earth has pulled together all of the disparate sources of
seafloor bathymetry into one
easy
-to-use package. Changes in the depth of the seafloor are shown in shades of blue:
the darker the blue, the greater the depth.
Tip:
Be patient as you work through this exercise
–learning a new tool like this requires
expe
rimentation. Earlier versions of this exercise have been vetted by several
undergraduates for ease
-of-use; it should take you less than an hour to complete. These
instructions were created on a Mac, but they should be easily understood if working on a
PC.
The TAs will be lenient in their grading of your assignments. Just try to do your best.
You should already have downloaded the desktop version of Google
Earth at:
https://
www.google.co
m/earth/download/gep/agree.html
And you should be somewhat comfortable with the controls after doing the previous
discussion exercise.
Creating a bathymetric profile of the Atlantic
seafloor
Open Google Earth and make sure that all “Layers” along the low
er left column are
unchecked except for Terrain at
the very bottom. Using the Add Path tool (outlined below),
draw a line from Washington, DC (38.891°N,77.009°W
–just cut and paste these
latitude/longitude coordinates into GE’s search box) to the northwes
t coast of Africa (maybe
around 22.242°N,15.757°W).
Once you choose the Add Path tool, a window will pop up asking you to name the path. Call it
Atlantic Profile or something similar. Then, while in the window, go to “Altitude” and choose
“Clamped to sea floor.” The name
of the Path will show up in your “Places” box along the
left column.
Now, with the Path name highlighted in Places, go up to Edit and choose “Show
Elevation
Profile.” (Right
-clicking will work, as well.) You’ll see a bathymetric profile of the seafloor
between the two endpoints that should look something like the image below.
As you move your cursor along the profile at the bottom in GE, you can track your location
along the path on the map above. Based on what you know from the GEL1 lecture, what
are the two shallow regions adjacent to the continents?
(continental margins)
Wha
t is the
jagged, somewhat symmetrical feature in the middle of the profile/path?
(Mid
-Atlantic Ridge)
What are the deepest parts of the profile called and what is their depth?
(abyssal
plains, ~17,000’ or ~5200 m)
Take a screenshot and call it
YourLastNam
e_Atlantic
. Label each of the different
bathymetric features directly on the image (either with your computer or by hand), then
submit
that image (with that file name!) to Assignments as part of the exercise.
Visiting the deepest point on Earth
Type “Cha
llenger Deep” into the search box and let GE take you to the deepest point on
Earth. (Click the “N” at the top of the upper compass wheel to keep North at the top of your
view. Hold and rotate the “N” around the compass to see different perspectives.) Begi
n at an eye altitude around 2600 miles (4200 km) (It doesn’t have to be exact, just high enough
so you see the bigger picture). Where are you on Earth?
(western Pacific Ocean)
Zoom in close enough to explore the dark arcing band in which the Challenger De
ep is
located. It’s called the Marianas Trench and it parallels the Marianas Island chain. Can you
guess why the deep ocean trench has an arcuate shape? Think of cutting an apple while
holding the knife at relatively flat angle to the apple’s surface. What
shape of cut do you
create on the surface of the apple?
Using your cursor to explore around the marker for the Challenger Deep, what is the
greatest water depth you can find? (Alternatively, look it up on Google.)
(~ 36,000’ or
~11,000 m)
Using the instr
uctions above for using the Path tool and creating an Elevation
Profile, make a path/profile
perpendicular to the Marianas Trench, passing close by the
Challenger Deep. The profile doesn’t have to be too long, maybe a 1000 miles (1600 km)
or so.
By moving your cursor along the profile, what is the maximum water depth on your profile?
(mine was
~3
3,000’ or 10,000 m)
What is the approximate width of the trench?
(mine was ~70 miles or 110 km)
Take a screenshot and call it
YourLastName_Pacific
. Submit
that image (with that file name!) to Assignments as part of the exercise. No need to label.
Exploring the seafloor on your own
Wander the world seafloor with GE until you find someplace that you think is interesting.
Maybe the Caribbean Sea, or the Arctic Sea, or the California continental margin, or the
South China Sea, or the Ross Sea off Antarctica,
or anywhere you want. Choose a region,
take a screenshot and label it
YourLastName_YourRegion
(e.g., Smith_ArcticSea). See if
you can identify any significant seafloor features (e.g., underwater volcanoes, deep
trenches, mid
-ocean ridges, fracture zones, a
byssal plains, continental shelves and slopes).
Label any features that you can and
submit
the image to Assignments.
GEL 1 Discussion Section
Exploring the Seafloor
Goal: To visualize bathymetric features of the ocean basins so that their tectonic
significance is more easily understood.
Introduction: Seventy percent of the surface area of Earth is concealed from view beneath
the world’s oceans. Most tectonic plate boundaries occur on the seafloor and are thus a
challenge to recognize. Methods of mapping the seafloor include sophisticated updates of
echo-sounding combined with massive computer firepower, and satellite measurements
of variations in sea level due to differences in the gravitational pull of the solid crust
beneath the oceans.
Google Earth has pulled together all of the disparate sources of seafloor bathymetry into one
easy-to- use package. Changes in the depth of the seafloor are shown in shades of blue:
the darker the blue, the greater the depth.
Tip: Be patient as you work through this exercise – learning a new tool like this requires
experimentation. Earlier versions of this exercise have been vetted by several
undergraduates for ease-of-use; it should take you less than an hour to complete. These
instructions were created on a Mac, but they should be easily understood if working on a
PC.
The TAs will be lenient in their grading of your assignments. Just try to do your best.
You should already have downloaded the desktop version of Google
Earth at: https://www.google.com/earth/download/gep/agree.html
And you should be somewhat comfortable with the controls after doing the previous
discussion exercise.
Creating a bathymetric profile of the Atlantic seafloor
Open Google Earth and make sure that all “Layers” along the lower left column are
unchecked except for Terrain at the very bottom. Using the Add Path tool (outlined below),
draw a line from Washington, DC (38.891°N,77.009°W – just cut and paste these
latitude/longitude coordinates into GE’s search box) to the northwest coast of Africa (maybe
around 22.242°N,15.757°W).
Once you choose the Add Path tool, a window will pop up asking you to name the path. Call it
Atlantic Profile or something similar. Then, while in the window, go to “Altitude” and choose
“Clamped to sea floor.” The name of the Path will show up in your “Places” box along the
left column.
Now, with the Path name highlighted in Places, go up to Edit and choose “Show Elevation
Profile.” (Right-clicking will work, as well.) You’ll see a bathymetric profile of the seafloor
between the two endpoints that should look something like the image below.
As you move your cursor along the profile at the bottom in GE, you can track your location
along the path on the map above. Based on what you know from the GEL1 lecture, what
are the two shallow regions adjacent to the continents? (continental margins) What is the
jagged, somewhat symmetrical feature in the middle of the profile/path? (Mid-Atlantic
Ridge) What are the deepest parts of the profile called and what is their depth? (abyssal
plains, ~17,000’ or ~5200 m)
Take a screenshot and call it YourLastName_Atlantic. Label each of the different
bathymetric features directly on the image (either with your computer or by hand), then
submit that image (with that file name!) to Assignments as part of the exercise.
Visiting the deepest point on Earth
Type “Challenger Deep” into the search box and let GE take you to the deepest point on
Earth. (Click the “N” at the top of the upper compass wheel to keep North at the top of your
view. Hold and rotate the “N” around the compass to see different perspectives.) Begin at
an eye altitude around 2600 miles (4200 km) (It doesn’t have to be exact, just high enough
so you see the bigger picture). Where are you on Earth? (western Pacific Ocean)
Zoom in close enough to explore the dark arcing band in which the Challenger Deep is
located. It’s called the Marianas Trench and it parallels the Marianas Island chain. Can you
guess why the deep ocean trench has an arcuate shape? Think of cutting an apple while
holding the knife at relatively flat angle to the apple’s surface. What shape of cut do you
create on the surface of the apple?
Using your cursor to explore around the marker for the Challenger Deep, what is the
greatest water depth you can find? (Alternatively, look it up on Google.) (~ 36,000’ or
~11,000 m) Using the instructions above for using the Path tool and creating an Elevation
Profile, make a path/profile perpendicular to the Marianas Trench, passing close by the
Challenger Deep. The profile doesn’t have to be too long, maybe a 1000 miles (1600 km)
or so.
By moving your cursor along the profile, what is the maximum water depth on your profile?
(mine was ~33,000’ or 10,000 m) What is the approximate width of the trench? (mine was
~70 miles or 110 km) Take a screenshot and call it YourLastName_Pacific. Submit that
image (with that file name!) to Assignments as part of the exercise. No need to label.
Exploring the seafloor on your own
Wander the world seafloor with GE until you find someplace that you think is interesting.
Maybe the Caribbean Sea, or the Arctic Sea, or the California continental margin, or the
South China Sea, or the Ross Sea off Antarctica, or anywhere you want. Choose a region,
take a screenshot and label it YourLastName_YourRegion (e.g., Smith_ArcticSea). See if
you can identify any significant seafloor features (e.g., underwater volcanoes, deep
trenches, mid-ocean ridges, fracture zones, abyssal plains, continental shelves and slopes).
Label any features that you can and submit the image to Assignments.