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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

Avalanches….

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


At the cmb

…at the CMB

CORE

MANTLE

MANTLE


Richard a muller hero http muller lbl gov

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)


Earth structure the cmb and d

Earth Structure- the CMB and D’’


How will they form i hear you say

How will they FORM I hear you say?

Please don’t let Charlie bite my finger…


Let it snow let it snow

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?


Meteor impact

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.


What would they do i hear you say

What would they DO I hear you say?


Consequence numero uno

Consequence numerouno

  • Trigger the disturbance of the geodynamo

    • Implications for magnetic reversals


Geodynamo

Geodynamo

  • SlumpingHeat 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


Geodynamo cont

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


Consequence numero dos

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)


Consequence numero dos1

Consequence numero dos

  • Mantle plume initiation

    • Flood Basalts and Kimberlites


Avalanches

  • 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)


A grand unified theory mass extinctions

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?


Evidence for linking reversals to impacts

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)??


Geomagnetic quiet periods

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.


Multiple avalanches

Multiple avalanches…

Slope recharge after 35Ma

Crater subduction- candidates?

Marine Extinction peak at 120Ma


Links to the chandler wobble

Links to the Chandler Wobble?

  • Decadal variations in avalanching

    • Small avalanches more likely and thus common than larger ones


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