1 / 21

Avalanches…. - PowerPoint PPT Presentation

  • Uploaded on

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).

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about ' Avalanches….' - franz

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript


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

At the cmb
…at the CMB




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)

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.

Consequence numero uno
Consequence numerouno

  • Trigger the disturbance of the geodynamo

    • Implications for magnetic reversals


  • 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

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

  • 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


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