Download Name: Date:______ Period:______ Lab – Sea Floor Spreading

Name:______________________
Date:__________ Period:______
Lab – Sea Floor Spreading
Introduction: Sea floor spreading is the hypothesis that the sea floor moves sideways
away from the mid ocean ridge. The two sides of the ridge are moving in opposite
directions leaving a rift valley that is the site of submarine volcanic eruptions.
Molten rock from a magma chamber only 1 to 2 kilometers below the central rift
valley feeds up to the spreading rift. The magma fills the crack between separating
crustal plates. It is estimated that 20 volcanic eruptions occur each year along Earth’s
mid ocean ridges and that every year 2.5 kilometers of new sea floor is formed in the
process.
Objective: Using data from the ocean floor, you will construct an ocean bottom profile.
Vocabulary:
Sea floor spreading –
Mid ocean ridge –
Subduction Rift valley –
Harry Hess –
Sonar –
Continental shelf –
Seamounts Procedure – Ocean Profile
1. Label the X-axis of the graph as “Distance from Coast (km)”
2. Label the Y-axis of the graph as “Depth (km)”
3. Using the data table provided, plot the data on the graph provided.
4. Label the following on the graph: mid ocean ridge, rift valley, continental shelf,
deep ocean floor and sea mounts
Procedure – Magnetic Stripes
1. Plot the data provided onto the graph provided as a bar graph.
2. If there is a North polarity for an age of the crust, color the bar as blue.
3. If there is a South polarity for an age of the crust, color the bar as red.
Data – Ocean Profile
Distance (km)
0
120
200
400
490
620
680
720
2000
2500
2900
3000
3090
3100
3200
Depth (km)
0
-0.2
-2.7
-3.7
-3.7
-4.6
-1.8
-4.6
-4.6
-4.0
-2.7
-1.8
-4.0
-2.4
-2.9
Distance (km)
3500
3600
3650
4025
4050
4100
4125
4500
5000
5300
5800
6000
6075
6100
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North Atlantic Ocean Bottom Profile
Depth (km)
-3.5
-3.7
-3.7
-4.0
-2.7
+0.5
-2.2
-4.6
-5.0
-4.4
-3.7
-2.7
-0.2
-0
-----
Data – Magnetic Stripes
Polarity Changes Seen on the Ocean Bottom
Analysis Questions:
1. What prominent sea floor feature is found in the central Atlantic Ocean?
2. What feature is found at a distance of 4,100 kilometers on the ocean bottom profile
you constructed?
3. What motions create the rift valley?
4. What happens to the age of rocks as you move away from the ridge?
5. What do you observe about the polarity of rocks on both sides of the ridge?
6. Explain why looking at magnetic stripes provides evidence for sea floor spreading?
7. Crustal plates are estimated to move at a speed of 3 centimeters per year. How long
will it take the plates to move 1 kilometer?
Conclusion:
Describe the features on the bottom of the sea floor and how they are created based on
sea floor spreading. What is happening to the Atlantic Ocean? Pacific Ocean?