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Magma Characteristics and Eruptions

Question:

How are volcanic eruptions related to properties of magma?

Background:

The table has data for 16 volcanic eruptions. The eruptions are rated by eruptive violence, magma viscosity, silica content in the magma and water content in the magma. Silica (plural silicates) are minerals that are compounds of silicon and oxygen. On scatter plot 1 you will plot data referencing the silica content. The water content of a magma will vary based upon the source of the rocks that melted to form the magma. On scatter plot 2, the water content data will be plotted.

Scatter Plot 1 (SILICA SiO2) Procedure:

  1. From the table, find the eruptive violence and magma viscosity for a volcanic eruption. Locate the appropriate square on the scatter plot y-axis for the eruptive violence and the square on the x-axis for the magma viscosity. In this intersection place a H or L depending if the eruption's magma silica content was high or low.
  2. As an example, Mt. Etna in Sicily has been plotted for you. This eruption had a moderate eruptive violence and medium magma viscosity. The silica content of the magma was high so a H was placed in the center square of scatter plot 1.
  3. Repeat step 1 for all the eruptions listed in the table.

Scatter Plot 2 (WATER H2O) Procedure:

  1. As you did for scatter plot 1, after locating the appropriate square on the y-axis for the eruptive violence and the square on the x-axis for the magma viscosity, plot a H or L depending on the eruption's water content.
  2. Mt. Etna in Sicily has again been plotted for you. An L was plotted because the magma's water content was low.
  3. Repeat step 1 for all the eruptions listed in the table.
 

Eruption Data Table

 

Volcano Location Year Type Eruptive Violence Magma Viscosity Magma SiO2 Content Magma H2O Content Eruption Products
Etna, Sicily 1669 Strato moderate medium high low lava,ash,cinders
Tambora, Indonesia 1815 Strato (caldera) high high high high ash,cinders,gas
Krakatoa, Indonesia   1883 Strato (caldera) high high high high ash,cinders,gas
Pelle, Martinique 1902 Strato (dome) high high high high gas,ash
Vesuvius, Italy 1906 Strato moderate medium high low lava,ash
Lassen, CA 1915 Strato (cinder) moderate high high low ash,cinders
Mauna Loa, HI 1933 Shield low low low low lava
Parcutin, Mexico 1943 Cinder moderate medium high low ash,cinders
Surtsey, Iceland 1963 Shield moderate low low high lava,ash
Kelut, Indonesia 1966 Strato (cinder) high high high high gas,ash
Arenal, Costa Rica 1968 Strato high high high low gas,ash
Helgafell, Iceland 1973 Shield moderate medium low high lava, ash
Mt. St. Helens, WA 1980 Strato high high high high gas,ash
Laki, Iceland 1983 Shield moderate medium low high lava,ash
Kilauea Iki, HI 1987 Shield low low low low lava
Fernandina, Galapagos 1994 Shield low low low low lava
 

Scatter Plot 1 - Silica (SiO2) Content

Name:

 

Eruptive Violence High
 
 
 

 
 
 

 
 
 
Moderate
 
 
 

H
 
 

 
 
 
Low
 
 
 

 
 
 

 
 
 
Magma Viscosity Low Medium High

 
 
 

Scatter Plot 2 - Water Content

 

Eruptive Violence High
 
 
 

 
 
 

 
 
 
Moderate
 
 
 

L
 
 

 
 
 
Low
 
 
 

 
 
 

 
 
 
Magma Viscosity Low Medium High
 

Questions:

  1. What is the relationship between the magma viscosity and the eruptive violence?
    1. If magma viscosity is high, the eruptive violence will be __________________________.
    2. If magma viscosity is medium, the eruptive violence will be __________________________.
    3. If magma viscosity is low, the eruptive violence will be __________________________.
  2. Which has the higher water content: a high or low viscosity magma?

     
  3. What is the relationship of the magma's composition (SiO2, H2O) to the types of materials (ash, lava, etc) ejected from the volcano during an eruption?
    1. If the magma's silica and water content are both high, the volcano ejects __________________________.
    2. If the magma's silica and water content are mixed (high and low), the volcano ejects __________________________.
    3. If the magma's silica and water content are both low, the volcano ejects __________________________.
  4. How is the magma viscosity related to its silica (SiO2) and water (H2O) content ?

     

     
  5. What is the relationship between the magma's composition (SiO2, H2O) and the specific type of volcano (strato, cinder, etc) produced?
    1. If the magma's silica and water content are both high, the volcano will be a __________________________.
    2. If the magma's silica and water content are both low, the volcano will be a __________________________.