Ocean Floor Magnetics

Part 1: Map view-color contoured for magnetics

1. Select DNAG magnetics under Image.

2. Select all the default options as you did before.

3. Notice the colored patches and lines. These are the areas where we have data. The black areas are regions with out available data. Therefore, to see the relationship of magnetism to the ocean ridges you must zoom in either on the Juan de Fuca ridge or the section of the Mid Atlantic ridge just south of Iceland. Position the box just off shore of the Washington centered on the Juan de Fuca ridge. Press <Enter> and wait for the image.

Note: You can add geographic boundaries to the map for clarity. Press <Enter> to return to the menu. Select Boundaries. Toggle through the options with the <Enter> key. Type a "y" for yes for Coastline. Choose Black for color and Detail. Press <Enter> several times to skip the other options and return to the menu, Select Go.

Q-1 What do the colors on this map represent?

Q-2 Can you recognize the symmetry of the magnetic stripes about the ridge?

Q-3 Use Ctrl P to explore the values of magnetics in nT (nanotesla). What colors are positive, what are negative?

Q-4 What is the difference between positive and negative magnetism of the ocean crust, in regards to the earth's magnetic field?

Q-5 Explain why the recognition of the patterns of magnetic stripes was such a revelation for Vine, Mathews, Hess and Cox.

Part 2: Map view-color contoured for topography with magnetic contour lines

1. Bring up the image Topography (N. America). Position a square box the same region west of Washington and Oregon.

2. Display contoured gravity by selecting Contours from the blue menu. Select DNAG Magnetics at a contour interval of 600 nT.

Q-1 How are the magnetic stripes oriented in comparison to the ridges?

Q-2 Notice that one set of stripes has a kink in its orientation. What does this suggest about the history of plate motions in this area?

3. Creating a useful image on a black ink printer will require you to adjust the colors assigned to topographic intervals. Follow the instructions below to make the ocean white and the continent gray.

A. Return to the blue menu screen. Select Topography (N. America) but before you display it select New when toggling through the Palette options.

B. The "help panel" at the top of the screen will instruct you as to how to re-assign colors to topographic intervals. Expect to make several attempts before succeeding at this task.

C. When the image looks good press Print Screen, open L-View and Paste in the image.

D. Give the image an appropriate title. Save and print it. Leave it on the screen for the next set of instructions.

Part 3: Profile of topography and magnetics

1. Using Ctrl-P, make an east-west profile across the region that includes part of the continent.

2. To add a profile of magnetics press F1 and select Mag 2.5'.

Q-1 Can you recognize the symmetry of the magnetic stripes about the ridge?

3. Modify, save and print this profile using L-View.