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Avalanches….

Avalanches…. None of this whatsoever has been proven. But that’s what fun about it. …at the CMB. CORE. MANTLE. MANTLE. Richard. A. Muller- hero. http://muller.lbl.gov/. Avalanches at the Core-Mantle Boundary, Geophysical Research Letters , vol 29 pp 41-1 to 41-4 (2002).

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Avalanches….

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  1. Avalanches…. None of this whatsoever has been proven. But that’s what fun about it

  2. …at the CMB CORE MANTLE MANTLE

  3. Richard. A. Muller- hero.http://muller.lbl.gov/ Avalanches at the Core-Mantle Boundary, Geophysical Research Letters, vol 29 pp 41-1 to 41-4 (2002)

  4. Earth Structure- the CMB and D’’

  5. How will they FORM I hear you say? Please don’t let Charlie bite my finger…

  6. Let it snow, let it snow… • 70% of density change as liquid core solidifies is due to exclusion of lighter element exclusion- leads to convection. • Excluded light elements remain in solution and freeze out as they rise (1000oC temp drop I.C to CMB) • Light elements fall like snow onto undulating surface of CMB • Gathers like snow…how nice… • Exceeding the angle of repose will cause slumping, bringing core liquid with it. • Only need a few degrees slope. • Shear stress causes slumping- oblique impact?

  7. Meteor Impact • Must be oblique • Consider, for example, a comet with velocity 25 km/sec, radius 5 km • ΔΩ = mvR/I • If the magnetic field of the core is coupled to entrained Fe in the sediment, sudden acceleration could cause an avalanche.

  8. What would they DO I hear you say?

  9. Consequence numerouno • Trigger the disturbance of the geodynamo • Implications for magnetic reversals

  10. Geodynamo • Slumping Heat re-distribution as cool precipitate mixes with hot liquid Fe, cooling the Fe and letting it fall due to density increase. • This may disturb large convection cells of the outer core, reduce the overall scale of flow and even change the dipole component. • Cells in close association may be also affected, driving an overall shut down of the geodynamo

  11. Geodynamo cont… • When the convective cells re-establish themselves, there is a 50% chance the magnetic field will reform in the reversed direction. I’m lost too mate…must be the geodynamo again. Game of chess? Help. I have absolutely no idea where the hell I am

  12. Consequence numero dos • Mantle Plume initiation • The part of the mantle that lost the ‘sediment’ blanket is exposed to hot Fe and rapidly heated • Maybe only from the largest of avalanches (thickness >>100m)

  13. Consequence numero dos • Mantle plume initiation • Flood Basalts and Kimberlites

  14. Mantle plume initiation • Flood Basalts and Kimberlites If several avalanches are coupled from an intense impact, could result in separate but simultaneous plumes e.g simultaneous but spatially distant plumes at 61-62Ma (Larson et al. 1999)

  15. A grand unified theory- MASS EXTINCTIONS • Meteor impacts and flood basalts have long been possible explanations for mass extinctions. • Flood basalts almost always seem to post-date the main phase of extinction • This would be satisfied by the impact avalanche model TIME??? Mantle plumes take millions of years to reach the surface- would destroy correlations. Kimberlite rates- 300km/s?

  16. Evidence for linking reversals to impacts • Reversal in fall back breccia of 24-km Reis impact crater. • No reversal occurs with Chicxulub crater • Ooooooooooo….. • High iridium suggests impact was vertical (would have been ejected to space if oblique)??

  17. Geomagnetic quiet periods • 120-85Ma has no magnetic reversals • Linked to mantle plume activity (Larson and Olsen 1991) which created Ontong-Java plateau • The LARGEST, yes, the largest, volcanic province on Earth. Alaska, 30Km thick.

  18. Multiple avalanches… Slope recharge after 35Ma Crater subduction- candidates? Marine Extinction peak at 120Ma

  19. Links to the Chandler Wobble? • Decadal variations in avalanching • Small avalanches more likely and thus common than larger ones

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