Copy of GS108 Lab 2 Geology of the Seafloor
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School
Linn Benton Community College *
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Course
108
Subject
Geology
Date
Feb 20, 2024
Type
Pages
8
Uploaded by EarlOtter2896 on coursehero.com
Name ______
Sage Clark
______________
Lab 2—Geology of the Seafloor
GS108
Key Ideas
To become familiar with seafloor bathymetric features and their relationships to tectonic
boundaries.
Objectives
a) Identify seafloor features such as seamounts, ridges, trenches, and abyssal plains
b) Calculate seafloor spreading rates
c) Compare and contrast relief of mountains on the seafloor and on land
Procedure
This lab has one part.
●
Part 1: You will use the NOAA Ocean Digital Atlas online mapping tool to
locate and identify geologic features of the Atlantic Ocean Basin.
●
Part 2: You will calculate seafloor spreading rates at two locations in the
Atlantic Ocean and determine a reason for why they are different.
●
Part 3: You will use the NOAA Ocean Digital Atlas online mapping tool to
locate and identify geologic features of the Pacific Ocean Basin.
●
Part 4: You will compare and contrast the elevations of Mauna Kea and Mt.
Everest.
Submission
Please submit a PDF to Moodle by Sunday at 11:59 pm.
Criteria
This lab is worth 10 points and will be graded using a rubric on Moodle.
1
Background
What do you imagine is on the bottom of the deep ocean floor? Do you picture it as a
big, smooth bathtub with green slime on the bottom and perhaps a few giant fish
swimming around in the dark, freezing cold? The ocean floor has this and more! In fact,
all of the major landforms that we find on the continents (mountains, valleys, plains,
gigantic canyons, etc.) are found on the ocean floor as well. It is anything but smooth!
Mountains Under the Sea
There are 2 common types of mountains on the
seafloor, both volcanic:
mid-ocean ridges/rises
and seamounts
.
Mid-ocean ridges
are long, linear volcanic ridges
formed where the seafloor fractures into 2 plates of
oceanic crust that spread away from each other.
The cracks between the diverging plates of
lithosphere are filled with magma that rises from the
mantle beneath mid-ocean ridges, and solidifies into new oceanic crust along the crest
of the mid-ocean ridge. Repeated cycles of cracking, spreading, melt injection, and
solidification of new crust along mid-ocean ridges over long periods of time (tens to
hundreds of millions of years) produces large plates of oceanic lithosphere that floor
entire ocean basins. For this reason, we say that the seafloor is "born" or "created" at
the mid-ocean ridges. Rises have gentler slopes and are not as steep.
Seamounts
Seamounts
are submerged volcanoes on the
seafloor. They may be active or extinct, and may
occur as isolated peaks, as groups, or as linear
chains. These regions of activity may be
associated with mid-ocean ridges, as is the case
with Axial Seamount to the left (source: NOAA),
with hot spots in the mantle (as is the case with
Loihi Seamount, which will one day become the
newest island of Hawaii).
2
Other Features Under the Sea: Trenches, Fracture Zones, Abyssal Plains
Subduction zones are places where an oceanic plate is bending down into the mantle
and sinking (subducting) beneath another oceanic or continental plate. A very deep
trench is formed parallel to the zone of collision. Here in the Pacific Northwest, there is
the Cascadia Subduction Zone that separates the Juan de Fuca Plate from the North
American Plate. We also have the Juan de Fuca Ridge, a spreading center or
mid-ocean ridge near us, acting as the boundary between the Juan de Fuca Plate and
the Pacific Plate. (Image: Oregon Department of Geology and Mineral Industries)
In referring to mid-ocean ridges
and subduction zones we have
really been talking about major
plate tectonic boundaries.
Mid-ocean ridges are places where
new plates are formed and
subduction zones are places where
plates are destroyed. A transform
fault is a third type of plate
boundary. This is where plates
slide past each other.
The San Andreas fault in California is such a
place (see USGS photo, left). Or on a more
detailed scale, portions of the mid-ocean ridge are
often separated by smaller transform faults that
form where the diverging plates are slipping
laterally past each other. The rugged topography
resulting from the deformation of the seafloor
along transform faults is carried away with the
spreading plates and
forms inactive extensions
of the transform faults, called
fracture zones
.
The seafloor also has huge, flat, deep areas where sediments
have buried the rough volcanic terrain that was created at
mid-ocean ridges. These places are called
abyssal plains
.
In this lab, you will use a very beautiful map that depicts what
Earth would look like if all the water were drained out of the
oceans. The map will show you all the above features. Study the
map carefully and answer the questions below.
3
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