Geology 1421 Online Assignment
Igneous Rocks and Volcanoes

Instructions:

Print out this assignment and go to the web sites to answer the questions.

Go to the web site for Minerals, Magmas and Volcanic Rocks at Volcano World.

  1. What are the 8 most abundant elements in the Earth's crust in order of abundance, and give the weight percentages of each?
    Element Weight %
    1 _______________ __________
    2 _______________ __________
    3 _______________ __________
    4 _______________ __________
    5 _______________ __________
    6 _______________ __________
    7 _______________ __________
    8 _______________ __________

  2. Based on your answers to the above, which two elements would you expect to be a part of most of the minerals and rocks of the Earth's crust?

     

     

  3. What is the name given to the major group of minerals that contains these two elements?

     

     

  4. Describe the silica tetrahedron.

     

     

  5. List the light-colored silicate minerals.

     

     

  6. List the dark-colored silicate minerals.

     

     

  7. Dark-colored minerals contain which two chemical elements?

     

     

  8. These dark-colored minerals are often referred to as mafic or

    ______________________________ minerals.

  9. Distinguish between intrusive and extrusive igneous rocks.

     

     

  10. Examine the table below, from Volcano World. 
     Classification of volcanic rocks by silica content. 

________________________________________________________________________

                Basalt          Andesite        Dacite          Rhyolite
________________________________________________________________________

SiO2            48-52           52-63           63-68           >68
FeO             10-12               7               5             2.5
MgO             10- 6               3               2            ~1
Na2O                3               3.5             3.8           3.5
K2O                 1               1.5             2.2           4.3
________________________________________________________________________
All numbers are in weight percent.
  11. What is the weight percent of SiO2 in the basalt?

     

     

  12. What is the weight percent of SiO2 in the rhyolite?

     

     

  13. What is the dominant type of igneous rock in Hawaii?

     

     

  14. How does the composition of Hawaiian volcanic rock compare and contrast with that of rocks from Mt. St. Helens?

     

     

  15. Viscosity of a magma is influenced by its ________________________ content.

  16. Magmas or lavas that are very fluid have _______________________ silica.

  17. Magmas or lavas that are very sticky have _______________________ silica.

  18. How does lava composition influence the shape of volcanoes?

     

     

     

     

    Comparing the compositions of rock from Hawaii and Mt. St. Helens

    Examine the diagram above and answer the following questions:

    SiO2 = silica, Al2O3 = Aluminum oxide, FeO = total iron oxide, MgO = magnesium oxide, CaO = calcium oxide, Na2O = sodium oxide, K2O = potassium oxide, TiO2 = titanium oxide, Other = other elements. Values are weight percent oxide.

  19. Rock from which locality has the greatest amount of silica?

     

     

  20. How is the amount of silica related to the viscosity of lava?

     

     

  21. Based on silica composition, which volcano would be most explosive?

     

     

  22. Which rock has the greatest amount of iron and magnesium?

     

     

  23. How does the amount of iron and magnesium influence the color of the rock?

     

     

  24. Which common rock-forming silicate minerals contain iron and magnesium?

     

     

    Eruptive Stage and Composition of Rocks in Hawaii

    Two types of basalt common in Hawaii can be distinguished, based on their alkali element (Na2O+K2O) content at the same silica (SiO2) content. Tholeiitic basalts have low alkali element contents relative to alkali basalts at the same silica content. Each type of basalt can differentiate (or evolve) to a higher silica content through such processes as settling of olivine crystals or mixing with more evolved magmas. The relationship between eruptive stage and composition of rocks from specific volcanoes is explored in this activity. A plot of silica versus alkali element content is shown in activity 9. The plot is from Peterson and Moore (1987) and represents all the volcanoes of the Island of Hawaii (and Loihi).

    Examine the graph and answer the questions from Volcano World. Modified from Peterson and Moore (1987).

  25. Which volcanoes are tholeiitic?

     

     

  26. Which volcanoes are alkalic?

     

     

  27. Is Loihi tholeiitic or alkalic?

     

     

  28. Which volcano(es) is (are) in the preshield eruptive stage?

     

     

  29. Which volcano(es) is (are) in the shield eruptive stage?

     

     

  30. Which volcano(es) is (are) in the postshield eruptive stage?

     

     

  31. Which eruptive stages are characterized by low eruption rates and low eruption volumes?

     

     

  32. Which eruptive stage is characterized by high eruption rates and high eruption volumes?

     

     

  33. Based on these observations, outline the relationships between eruptive stage, eruptive rate, eruption volume, and chemical composition of Hawaiian eruptive products?

     

     

  34. How does the position of the volcano, relative to the hot spot, relate to eruptive stage and chemical composition of eruptive products?

     

     

    Volcanoes

    Examine the diagram below from Volcano World and answer the following questions. Note that the scales are different.

  35. The cinder cone is _____ feet across and _____ feet high.

  36. The stratovolcano is _____ miles across and _____ feet high.

  37. The shield volcano is _____ miles across and _____ feet high.

  38. Which volcanic landform is tallest?

  39. Which volcanic landform is widest?

  40. Which volcanic landform has the most gentle slopes?

     

    Drawing topographic profiles of volcanoes

    Go to the Profiles of the Volcanoes of the Island of Hawaii (Volcano World) and print out the page (or use the diagrams below).
    Draw the topographic profiles of the Hawaiian volcanoes and answer the questions.

    Use the profiles you draw to answer the following questions.

  41. Which volcano has the steepest slopes?

  42. Which volcano has the most gentle slopes?

  43. Which volcano is longest from summit to sea level?

  44. Which volcano has a triangular profile?

  45. Which volcanoes have shield-shaped profiles?

  46. Why are the slopes of Hualalai steeper than the slopes on Kohala?

     

     

  47. Why are the slopes on Mauna Kea steeper than the slopes on Mauna Loa?

     

     

  48. Is there a correlation between the stage of evolution of a volcano and the steepness of its slopes?

     

     

Take the Tour of Hawaii Volcanoes National Park. Follow each of the trails and click on each localilty. We will be discussing this area in class because I visited the area in Summer 1997. You will need to be somewhat familiar with the tour and the various features shown (Kilauea, Mauna Loa, Halemaumau, Mauna Ulu, Chain of Craters Road, Devastation Trail, etc.). I can't take you there in person, but if you work your way through each stop of the drives and trails, it will be the next best thing. Best of all, you can do this in the time it takes to drive to the airport. No need for a nine hour plane ride with a couple of layovers, AND you save $800! Aloha.

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This page created by Dr. Pamela J. W. Gore,
Georgia Perimeter College, Clarkston, GA
pgore@gpc.Peachnet.edu
Page created January 14, 1998.
Modified: January 26, 1998.
Address corrections Fall 1998.