Download NOAA Mid Oceanic Ridges

Name:________________________________________ Date:_____________Period:________
Lesson 2: Mid-Ocean Ridges
http://www.montereyinstitute.org/noaa/lesson02.html
The National Oceanic and Atmospheric Administration—NOAA—is a leader in exploring the geologic and
biologic mysteries of the deep-sea. Recently, NOAA sent an interdisciplinary exploration team of U.S.
and Canadian scientists to witness the birth of new ocean crust off the coast of western North America.
Directions: Fill in the blanks as you watch the video. You may need to pause as
you go to obtain all the necessary information.
1.
The Explorer Ridge, part of the Pacific “Submarine Ring of Fire”, lies just 60 nautical miles from the
northwest United States. It is one segment of the massive _______________________—a 65,000
km long series of seafloor spreading centers where new earth is created.
2.
NOAA’s “Submarine Ring of Fire Expedition,” has helped illuminate the ________ _________ at
work along mid-ocean ridges.
3. The nearly _______________, global mid-ocean ridge system snakes across the Earth’s surface like
the seam on a baseball. It is clearly visible on this map of global topography above and below sea
level.
4. The ridge system forms the ___________ and ____________ mountain range on Earth. It winds its
way between the continents and is more than 65,000 kilometers long and 1,500 km wide.
5. A steep-sided, flat-bottomed rift valley sits atop the crest of most ridges. This series of mountains
and valleys forms at ____________________ plate boundaries, where the Earth’s oceanic plates are
torn apart.
6. Here, where two pieces of the Earth’s crust pull away from one another and new __________
___________ is created in the gap between them, the surface of our planet is renewed.
________crust is recycled back into the _______ elsewhere on the globe, where plates collide.
7. _________ begins when tectonic activity pulls and stretches part of the oceanic crust, causing cracks
along a narrow, linear, ________ _______
8. As the plate thins, the underlying ______ starts to melt, and magma rises into the fracturing crust.
Because the rift zone becomes less ________ and more buoyant as it thins down and heats up, the
crust rises to form a ______ ______ on the sea floor.
Name:________________________________________ Date:_____________Period:________
9.
The basaltic magma oozes upward into vertical fissures in the crust. Most of the magma _______
and _________ while still within the plate. These upright columns of rock, called basaltic dikes, form
the bulk of the new _______ ______.
10. Sea floor eruptions occur from long _________ and undersea _______ that line the sides and
bottom of the rift valley. ________ pour from the fissures and across the surface of the seafloor,
adding a thin coat of new lava (typically <10 m thick) with each eruption.
11. Along the rift valley, divergence leads to volcanism that creates new oceanic crust, crust that is in its
turn _______ and _____________ by continued divergence and volcanism.
12. By this perpetual process, oceans -_____ and _______slowly but surely. An example occurs at the
Juan de Fuca Ridge, where the spreading process creates an average width of 6 m of new crust every
100 years.
13. The spreading rates of ridges vary. Some spread quite slowly, no more than _________ per year
while others spread at rates approaching _________ per year.
14. ___________ ___________ are laced with fractures and intruded by magma. Seawater seeps into
the oceanic crust and becomes extremely hot, as much as 400°C. The superheated water dissolves
________ and carries them along as it circulates through the crust. Eventually the mineral-laden
water rises back out of the crust, boiling into the bottom of the sea through ocean floor hot springs,
called _____________- _____________, scattered along the rift valley.
15. The creation of oceanic crust is one of the most important geologic processes on Earth.
Approximately ___________ __________ of the Earth’s surface is oceanic crust, all formed along
mid-oceanic ridges in just the last ___________ million years.
16. The _______________ ____________ is the most significant topographic feature on the sea floor,
and its activity has a profound impact on global sea level. When rapid sea floor spreading inflates
the ridges, enough water is displaced to raise sea level by hundreds of meters. When divergence
slows, the ridges shrink and the oceans draw away from the continental shelves.
Name:________________________________________ Date:_____________Period:________
Now Click on the Mid-Oceanic Ridge Activity on the right side of the screen.
Follow the directions on the screen starting with labeling the continents, then labeling the mid-oceanic
ridge divisions and finally labeling the ages of the oceanic crust from the Eastern Pacific Rise outward.
(Use the time scale at the bottom left of the screen to determine how the color and age of crust relate.)
Answer the following questions found underneath the interactive on that page.
a. Where is the youngest ocean floor located?
b. Where is the oldest ocean floor located?
c. There are rocks on every continent that are 3 to 4 billion years old. Why are there no oceanic
rocks older than 200 million years?
d. In the eastern Pacific, why are oceanic rocks no older than 120 million years?
e. Based on the distribution of color on the map, which ridge is spreading faster, the Mid-Atlantic
Ridge or the East Pacific Rise (ridge and rise are both nicknames for a mid-oceanic ridge)?
f.
Based on the distribution of color on the map, which ridge is spreading faster, the Mid-Atlantic
Ridge or the Southeast Indian Ridge?
g. How does the rate of spreading of the Southeast Indian Ridge compare to the Southwest Indian
Ridge?
h. If the mid-ocean ridges active today continue to produce new sea floor for another 100-200
million years, how will the appearance and location of oceans and continents be changed?
Close out of this activity and go back to the main page.
Click on the Sea Floor Spreading Activity and read the selection.
Move the slider bar left to reveal the magnetic view, which shows the invisible patterns of magnetic
polarity contained within the crust. Refer to the figure to answer the questions that follow.
1. Based on the diagram, how many times has the Earth's magnetic field reversed during the past
four million years?
2. Approximately when did the current interval of normal polarity begin?
3. If there had been compasses four million years ago, which direction would compass needles
have pointed?
4. Why are the magnetic stripes on the sea floor parallel to and symmetrical across the mid-ocean
ridge?