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Exploring Africa's Physical and Cultural Geography Using GIS
Activity 5: Earthquakes, Volcanoes, and Faults in Africa
Earthquakes, Volcanoes and Faults in Africa
Map of East Africa showing some of the historically active volcanoes (red triangles) and the Afar Triangle (shaded, center) -- a so-called triple junction (or triple point), where three plates are pulling away from one another: the Arabian Plate, and the two parts of the African Plate (the Nubian and the Somalian) splitting along the East African Rift Zone.
In East Africa, spreading processes have already torn Saudi Arabia away from the rest of the African continent, forming the Red Sea. The actively splitting African Plate and the Arabian Plate meet in what geologists call a triple junction, where the Red Sea meets the Gulf of Aden. A new spreading center may be developing under Africa along the East African Rift Zone. When the continental crust stretches beyond its limits, tension cracks begin to appear on the Earth's surface. Magma rises and squeezes through the widening cracks, sometimes to erupt and form volcanoes. The rising magma, whether or not it erupts, puts more pressure on the crust to produce additional fractures and, ultimately, the rift zone.
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In this exercise, you will examine the location of earthquakes and volcanoes in relationship to faults in Africa. You will also look at the impact on countries in Africa.
Note: New ArcView instructions will be explained in this Exercise. Please refer to Activities 1 through 4 for ArcView instructions that you have already completed.
| Step 1 | Start ArcView and start a project
Open ArcView GIS by accessing the ArcView shortcut or through the Programs Menu: Choose the project that you have been working on: In the Student temporary folder, look for the file "your team name.apr". In this activity, you will be creating new files. You will want to save your work to a directory on your hard drive. To change the default directory, click "File" and choose "Set Working Directory" from the pulldown menu. Type the path to the directory where you will save your work. This should be the "student temporary" directory, then click OK. |
| Step 2 | Create a new View
Click on Views in the project window on the left side, and click on "new." Click on the View pulldown menu at the top. Choose "Properties", and rename the view to "Faults, Earthquakes and Volcanoes in Africa". Select "decimal degrees" from the Map Units pull down list . Select "kilometers" from the Distance Units pull down list. Click on Projection and check to make sure the Category is "Projections of the World" and the Type is "Geographic". Click OK. |
| Step 3 | Add Africa Countries, Earthquakes, Volcanoes, Recent Volcanoes, Plate Boundaries and Faults to the view.
Add the following themes to the view from your Africa folder: The afr_eq.shp contains earthquakes greater than or equal to magnitude 6.5 on the continent of Africa. The volrecen.shp file only lists the last eruption of volcanoes that have been active within the last 50 years on the continent of Africa. The volafr.shp file contains all known volcanoes in historic and modern time periods on the continent of Africa. Add the following themes to the view from the esri_dat directory: The country.shp file contains the outlines of countries in Africa. The faults.shp file contains faults in Africa. A fault is a thin zone of crushed rock between two blocks of rock, and can be any length, from centimeters to thousands of kilometers. The popden.shp file contains population density information for Africa. |
| Step 4 | Rename the Themes
Rename the afr_eq.shp theme to Earthquakes6 |
| Step 5 | Display the Africa Faults as Unique Values
Double-click on the Africa Faults theme to bring up the Legend Editor. In the Legend Editor window select "Unique Value" as the Legend Type. Select "Type" for the Values Field. Double-click on the line symbol next to the value "rift" to bring up the Pen Palette In the Legend Editor window double-click on the line symbol next to the value "thrust". In the Pen Palette |
| Step 6 | Display the Population Density Theme as a Graduated Color
Double-click on the Population Density theme to bring up the Legend Editor. In the Legend Editor window select "Graduated Color" as the Legend Type. Select "Density" for the Classification Field. Select "Yellow Monochromatic" for the Color Range. Click Apply in the Legend Editor to apply your changes to the view. Leave the Legend Editor open. |
| Step 7 | Change the Colors, Sizes, and Symbols of the Themes
Change the colors, sizes, and symbols of the themes below. Remember to click Apply in the Legend Editor after changing each theme. |
| Step 8 | Arrange the Themes in the View Window
Arrange the themes in your view window in the following order: |
| Step 9 | Display the Themes in the View
Click on the raised box to the left of the Theme names to make a check mark and see the coverages displayed in the View window. You may want to turn off one or more themes in order to view the distribution of a particular theme. You may need to maximize or resize the ArcView window and the View window to see the entire view. |
| Step 10 | Zoom to the Continent of Africa
Make the Countries the active theme and click the Zoom to Active Theme button |
| Step 11 | Create and Print a Layout
Select three or four related themes and create and print a new Layout. For example, show recent and historic volcanoes, faults, and countries. |
Note: You may want to turn the Historic Volcanoes and Earthquakes themes off to view the Recent Volcanoes and faults in Africa for some of the questions below:
| Question 1 | Use the Information button  or use the Open Theme Table Button  to open the Recent Volcanoes table and determine which volcano in Africa last erupted. |
| Question 2 | Are the volcanoes in Africa located near plate boundaries or faults? |
| Question 3 | Which country in Africa has the most historic volcanoes? |
| Question 4 | Which country in Africa has the most recent volcanoes and is most at risk from volcanoes that may erupt in the future? |
| Question 5 | What areas in Africa have high population densities, 5-9, and also have some risk from earthquakes and volcanoes? |
*** End of Africa Activity 5 ***
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U.S. Geological Survey
URL: http://education.usgs.gov/common/lessons/act5.html
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Page Last Modified: Wednesday, 29-Aug-2007 10:43:15 EDT
. In the Pen Palette window change the size to 2. Click on the paintbrush icon to bring up the Color Palette 
. From the Color Palette choose a bright green. Leave the Legend Editor open.
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