1. Describe how the “hotspot” differs from the global
average in terms of temperature only.
Global Average/Ridge:
410-km disc.
“Normal,” ~1350° C
660-km disc.
Hawaii:
This activity is Part 2 of a series examining variations in mantle transition zone thickness, temperature, and composition. This activity should be paired with the phase diagrams and phase diagram instructor notes. The transition zone thickness measurements and temperature number for Hawaii are based on the result from the paired Temperature activity [Hawaii TZ thickness = ~225 km , corresponding to a temperature of +174 C], done in class or as homework before this assignment. I went through this slide/exampl in class, and so the answers/results for this slide are already filled in. This is a good opportunity to to introduce the phase diagram and demonstrate why the phase changes dictate a thin TZ for an increase in temp. In the previous activity, students should have established that the variation in TZ thickness beneath the East Pacific Rise is within error on estimates of average TZ thickness, so here “Global Average” and “Ridge” are depicted as equivalent.
410-km
Hotter
(+ 174 ° C)
660-km

2. Describe how the “hotspot” differs from the global
average in terms of iron (Fe) only.
Global Average/Ridge:
410-km disc.
“Normal”
660-km disc.
Hawaii:
410-km
660-km

3. Describe how the “hotspot” differs from the global
average in terms of water (H) only.
Global Average/Ridge:
410-km disc.
“Normal”
660-km disc.
Hawaii:
410-km
660-km

4. Transition Zone Thickness Summary
Question: Think about our observations of transition zone thickness…
Do any of the thermal or chemical scenarios (variations in temperature, iron, or water) make more or less sense than the others? If so, how could it be proved or tested?

5. Explain the tomography beneath Hawaii in terms of:
Temperature
Iron
Water

6. Tomography Summary Question: Think about the tomography…
Do any of the thermal or chemical scenarios (variations in temperature, iron, or water) make more or less sense than the others? If so, how could it be proved or tested?

7. Make a Decision Question: Consider it all…
What factors (temperature, iron, or water) do YOU conclude cause the observations beneath Hawaii? Why?
If more than one, how big a role does each one play? (Is one dominant over the others? Which one?)
Reminder for students: Just because one explanation may work better in this particular instance, that doesn’t mean that it is always right or that the others are always wrong for other places in the Earth!