1. Today – 4/04 Spring Winds Mineralogy of the Earth

2. Jetstream Monday 5 am

3. NWS Warnings Monday

4. Red Flag Warning Dangerous fire weather! Locally defined criteria Here: relative humidity below 15%, sustained winds of 20 mph and/or gusts of 35 mph, dangerous fuel conditions

5. Rodeo- Chediski Fire, 2002

6. Aspen Fire, 2003

7. Last Time Atomic scale structure of the core and lower mantle Figuring out mantle composition Lower mantle: negatively charged oxygens are big, smaller positively charge atoms (Mg, Si) are small, fit in between oxygens. Pressure forces oxygens close together, so each Si is surrounded by (bonded to) six oxygens

8. Stishovite, SiO 2 Little blue sphere = silicon atom Big red spheres = oxygen atoms

9. Possible Test Question Would you expect to find stishovite in the: a)Crust b)Upper mantle c)Lower mantle d)Core

10. Upper Mantle Same kinds and numbers of atoms as the lower mantle, but combined differently to form different minerals 70% olivine, 25% pyroxene, 5% garnet In olivine and pyroxene, silicon atoms are surrounded by four oxygens. In mantle garnets, half of the silicons are surrounded by four oxygens, half by six

11. Olivine

12. Olivine

13. Olivine

15. Pyroxene (Diopside)

16. Garnet (Pyrope)

17. Crust Oceanic – basalt Oceanic – basalt Basalt: 50% feldspar, 50% pyroxene Basalt: 50% feldspar, 50% pyroxene Continental – granite Continental – granite Granite: 30% quartz, 70% feldspar Granite: 30% quartz, 70% feldspar

18. Feldspar (Amazonite)

19. Quartz (Variety Amethyst)

20. Important Points Extreme conditions of the mantle limit the number of structure types to a handful, but huge variety in the low P, T crust Si bonded to 6 oxygens in lower mantle, 4 in upper mantle and crust Negatively charged oxygens thought of as big, with small positively charged atoms in the spaces between oxygens

21. Why is the Crust Different from the Mantle? When partial melting begins in the asthenosphere, the elements Si, Al, Na, and K migrate into the melt, while Mg and Fe stay put. The magma rises, preferentially separating out these elements. Additionally, minerals with lots of Mg and little Si crystallize out first, the second step in the mantle’s Mg loss prevention program

22. Why is the Crust Different from the Mantle? When rocks that are already enriched in Si and depleted in Mg in the lithosphere begin to melt again for some reason, the process repeats, widening the compositional gap between these “evolved” rocks and the mantle they originally came from

23. Why Do Rocks Melt? Decompression – MOR’s. As convecting hot rock rises, confining pressure is reduced, and the rock begins to melt Hydration – subduction zones. As a subducting slab goes down, water trapped in cracks and hydrous minerals is released into the overriding mantle. This lowers the melting point of the overriding rocks, and magma is generated

24. Geotherm

25. Decompression Melting 

26. Hydration Melting

27. Montserrat Tectonic Setting

28. Movie Notes and Questions How did the oceans and atmosphere form? Pyroclastic flow – cloud of hot gas, ash, and rock that flows down the side of a volcano at high speed Eruption mechanism How do the scientists predict eruptions? How high does the eruption column reach?