NOVA

Mystery of the Megavolcano

Student Handout

Volcano Suspects: Ash Composition


The following represents a breakdown of the average concentration of major compounds (percentage by weight) in the ash from each volcano.

Ash Sample

Aluminum Oxide
(Al2O3)

Calcium Oxide
(CaO)

Iron Oxide
(FeO)*

Potassium Oxide
(K2O)

Magnesium Oxide
(MgO)

Sodium Oxide
(Na2O)

Titanium Dioxide
(TiO2)

Phosphorous Pentaoxide
(P2O5)

Silicon Dioxide
(SiO2)

Mount St. Helens

14.70

1.81

1.39

2.01

0.46

4.45

0.17

0.04

74.80

Crater Lake

14.79

1.58

1.85

2.77

0.32

5.21

0.43

0.09

72.39

Lassen Peak

13.99

2.03

1.99

3.43

0.88

3.64

0.35

0.10

73.47

Long Valley Caldera

13.24

0.40

0.70

5.06

0.07

2.92

0.07

0.01

72.42

Valles Caldera

12.43

0.45

1.52

4.74

0.05

3.74

0.08

0.01

74.77

Bruneau-Jarbridge

11.90

0.80

2.70

6.10

0.10

2.50

0.10

0.08

75.60

Yellowstone Caldera

11.71

0.56

1.90

5.57

0.15

2.75

0.23

0.01

76.49

La Garita

12.50

0.56

1.10

4.80

0.01

2.38

0.10

0.02

77.10

*combined concentration of FeO and Fe2O3

Questions

  1. For each suspect volcano, would you characterize the magma that produced the ash sample as mafic, intermediate, or felsic? Why?

  2. Which ash seems to be most similar in composition to the Ashfall sample?

After you answer these questions, mark the "Volcano Suspects Table" on your "CSI: Ashfall Fossil Beds" handout with the volcano or volcanoes you feel is or are the least likely suspect(s) based on the data, and rate your confidence level in your answer.




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