Mystery of the Megavolcano
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Student Handout
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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
For each suspect volcano, would you characterize the magma that produced the
ash sample as mafic, intermediate, or felsic? Why? 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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