Avalanches….None of this whatsoever has been proven.

But that’s what fun about it

…at the CMB

MANTLE

CORE

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)

Earth Structure- the CMB and D’’

How will they FORM I hear you say?

Please don’t let Charlie bite my

finger…

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?

Let it snow, let it snow…

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.

Meteor Impact

What would they DO I hear you say?

Trigger the disturbance of the geodynamo◦ Implications for magnetic reversals

Consequence numero uno

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

When the convective cells re-establish themselves, there is a 50% chance the magnetic field will reform in the reversed direction.

Geodynamo cont…

Help. I have absolutely no

idea where the hell I am

I’m lost too mate…must be the geodynamo again. Game of

chess?

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 dos

Mantle plume initiation Flood Basalts and Kimberlites

Consequence numero dos

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)

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

A grand unified theory- MASS EXTINCTIONS

TIME??? Mantle plumes take millions of years to reach the surface- would destroy correlations.

Kimberlite rates- 300km/s?

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)??

Evidence for linking reversals to impacts

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.

Geomagnetic quiet periods

Multiple avalanches…

Slope recharge after 35Ma

Crater subduction- candidates?

Marine Extinction peak at 120Ma

Decadal variations in avalanching◦ Small avalanches more likely and thus common

than larger ones

Links to the Chandler Wobble?