Igneous Rock Chemistry and Volcanic Eruptions 5/14

Integrated Science 4 Name ______Per. _____

Introduction

Research and observations of volcanic activity produce two very different pictures of volcanic eruptions. The volcanoes of Hawaii and the Galapagos Islands are good examples of 'quiet' or 'gentle' eruptions, where low viscosity lava tends to flow rather than explode. These events, while not entirely benign, generally result in few injuries and relatively little property damage. In Hawaii, they are actually seen as good for tourism, attracting many people to watch the spectacular displays. Mt. Pinatubo and Mt. St. Helens are good examples of a different type of eruption. These mountains, and others like them, produce a violent, explosive eruptive event. These eruptions are more difficult to predict and often result in widespread destruction.

The main difference between these volcanic types lies in the chemistry of their magma. After erupting, these different magmas will solidify into many types of igneous rock. These differences in magma chemistry and rock type are, in turn, related to plate tectonics. Consequently, the chemical and structural composition of igneous rocks tells much about the processes– both the volcanic and plate tectonic– under which each was formed.

In this lab, we will look at these structural and chemical differences in an attempt to understand different eruptive patterns, the rock types they produce and their relationship to plate tectonics. Consider the following focus questions as you work:

• What are the differences in chemical composition between common igneous rocks?

• What is the connection between chemical composition of igneous rocks and the type of volcanic eruption which produced them?

• What is the connection between different types of volcanic eruptions and plate tectonics?

Procedure

1. Study the pie graphs in Figure 1, which provide a chemical analysis of the igneous rocks rhyolite, andesite and basalt. Complete the provided key and then shade the graphs to correspond to that key. You will use these graphs to interpret the unknown samples.

2. Data Table 1:Igneous Rock Chemistry, shows the compositions of four unknown volcanic rock samples. The amount of each substance in the rock is shown as a percentage of the total.

3.Construct a pie graph for each unknown volcanic rock in Figure 2. Compare your graphs to the known samples and review prior material regarding igneous rock to complete the Discussion and Conclusion questions.

Data

Figure 1.

Data Table 1: Igneous Rock Chemistry

Volcanic Rock 1
Iceland / Volcanic Rock 2
Mt. St. Helens / Volcanic Rock 3
East Pacific Rise / Volcanic Rock 4
Mt. Pinatubo
Silica / 49% / 60% / 47% / 73%
Aluminum
Oxide / 16% / 17% / 13% / 13%
Fe and Mg
oxides / 18% / 9% / 23% / 3%
Other / 17% / 14% / 17% / 11%
Total / 100% / 100% / 100% / 100%

Figure 2.

Discussion and Conclusion

  1. Complete Data Table 2. to summarize the relationship between plate tectonics, lava chemistry and igneous rocks. (Use all past work regarding Igneous Rocks).

Data Table 2. Plate Tectonics, Magma/Lava Chemistry & Igneous Rocks* The above table does not consider depth of formation or crystal size*

PROPERTIES / MINERAL COMPOSITION OF MAGMA, LAVA & IGNEOUS ROCKS*
Felsic / Andesitic / Mafic
Chemistry
Color
Density
Viscosity
Gas Content
Eruption Type
Plate Boundary Interaction
Features
  1. Identify the four 'unknown' volcanic rocks represented by each of the pie graphs by completing the table below. Use the chemical composition and location of each unknown volcanic rock to predict the type of plate boundary and the type of eruption that produced each rock.

Volcanic Rock 1
Iceland / Volcanic Rock 2
Mt. St. Helens / Volcanic Rock 3
E. Pacific Rise / Volcanic Rock 4
Mt. Pinatubo
Rock type
Plate boundary
  1. Predict the rock type that would occur at each of the following locations and explain why.

Location / Rock type / Explanation
Kilauea or Mauna Loa (Hawaii)
Mt. Shasta (California)
Mid-ocean ridges
Japanese Islands
  1. Predict the type of volcanic eruption that produces each of the following rock types and explain why.

Rock type / Volcano type / Explanation
rhyolite
basalt
andesite