Question on the wandering magnetic poles

[Nihil]

What is the boundary effect of the magnetic pole migrations?

I realise that this is a cyclical thing (~26000 years) and that it
has been recorded by igneous rocks (cf Atlantic bed magnetic patterns)
but could anyone point me to an "impact statement" of how this affects
the overlying crust?

I'm trying to get my head around *where* the boundary to the change
actually exists but haven't got access to my old geology texts at the
moment. Seem to recall it is in the mantle but would appreciate any
corrections.

The specific issue is that on the "outside" of this "boundary", the
direction of the magnetic field has changed to what it was shortly
before. If the two sides were originally in alignment then there will
be a misalignment after any movement. As the movement increases, this
misalignment will increase.

Even though the magnetic force is small (compared to the mass of the
materials involved), I would expect some kind of reaction ... but am
not sure as to how this would become apparent.

Is this realistic or just too much late-night musing?

Nihil

[trotsky]

1. I'm not sure I understand exactly what you're asking.

The changing magnetic field doesn't really impact solid crust. I mean, solid rocks don't exactly "care" which way the earth's dipole is pointing.

Scientific American did an awesome writeup several months ago of what exactly causes the earth's magnetic field and how it does the flip. If you have time, see if your local library carries back issues and flip back thru the last 6-8 months or so. IIRC, it is the cover story so it should be easy to find.

[Nihil]

2. Sorry - I'll try again!

There is a boundary between the zone where the Earth's dipole can
migrate/wander/flip and the zone where the magnetic field remains
static. From memory, this boundary is in the upper mantle as it
is somewhere below the solid crust (static) and the core (dynamic).

I was wondering what effect this differing magnetic force would
have on the convection cells in the mantle itself: even a small force
applied over time can affect a moving flow or object and the change
in magnetic orientation as the pole moves would provide a small force
on the magma flows.

How would these changes become apparent here on the surface?
Would there be a change in location of hotspots? Change in vulcanism
(on->off or off->on)? Increase in rate of earthquakes due to the changes
in stress under the crust?

Like I said, I was just musing about this last night and wondered if
anyone could enlighten me!

Thanks,

Nihil

[trotsky]

3. I think that Scientific American article would go a long way...

towards answering your question. It shows that the earth's dipole is far from monolithic, and the "flip" is more of a net change of tons of little dipoles caused by eddys and currents of molten iron.

The crust itself, as far as I know, does not have its own field. Magnetic particles can get aligned by the planetary field when they cool out of magma or lava, but they are not significant enough to effect the planet's field.

[Nihil]

5. Thanks

I believe the article is in the April 2005 edition so will read this
when I next visit my "SciAm librarian" (father-in-law).

[Dover]

4. I think this will answer your question

News
April 11, 2002

Satellites Spy Changes to Earth's Magnetic Field


Though the process can take nearly 5,000 years, the earth's magnetic field periodically reverses. According to a report published today in Nature, scientists may have detected the beginning of the field's next such reversal.

Motion of the earth's liquid core, the so-called geodynamo, generates its magnetic field. Gauthier Hulot of the Institut de Physique du Globe de Paris and his colleagues used satellite data recorded 20 years apart to track changes in this field. In two regions of the boundary between the earth's core and the overlying mantle, the researchers detected a reversed magnetic field. In a section lying beneath the southern tip of Africa, the magnetic field points toward the center of the earth—opposite to the dominant outward-pointing field of the Southern Hemisphere. And a second congregation of reversed-flux patches exists near the North Pole. Having modeled the growth and movement of these inverted-flux sections, they can now account for nearly the entire decrease in the main dipole field of the earth over the past 150 years.

http://www.sciam.com/article.cfm?articleID=000C56A1-0B6B-1CD0-B4A8809EC588EEDF

--------------------------------------------------------------------

Magneticosphere - Earth's Magnetic Field

All magnetic objects produce invisible lines of force that extend between the poles of the object. An easy way to visualize this is to spread iron filings on a sheet of paper and place a bar magnet under the paper. The iron filings will arrange themselves around the magnet and along the magnetic field lines.

In the simplest terms, Earth can be thought of as a dipole (2-pole) magnet. Magnetic field lines radiate between Earth's north and south magnetic poles just as they do between the poles of a bar magnet. Charged particles become trapped on these field lines (just as the iron filings are trapped), forming the magnetosphere.

All magnetic objects produce invisible lines of force that extend between the poles of the object. An easy way to visualize this is to spread iron filings on a sheet of paper and place a bar magnet under the paper. The iron filings will arrange themselves around the magnet and along the magnetic field lines.

In the simplest terms, Earth can be thought of as a dipole (2-pole) magnet. Magnetic field lines radiate between Earth's north and south magnetic poles just as they do between the poles of a bar magnet. Charged particles become trapped on these field lines (just as the iron filings are trapped), forming the magnetosphere.

Earth's magnetic field lines are not as symmetrical as those of the bar magnet. The impact of the solar wind causes the lines facing sunward to compress, while the field lines facing away from the Sun stream back to form Earth's magnetotail. The magnetosphere extends into the vacuum of space from approximately 80 to 60,000 kilometers (50 to 37,280 miles) on the side toward the Sun, and trails out more than 300,000 kilometers (186,500 miles) away from the Sun.

The cause of Earth's magnetic field (the surface magnetic field) is not known for certain, but is possibly explained by dynamo theory. The magnetic field extends several tens of thousands of kilometers into space.

The field is approximately a magnetic dipole, with one pole near the geographic north pole and the other near the geographic south pole. An imaginary line joining the magnetic poles would be inclined by approximately 11.3? from the planet's axis of rotation. The strength of the field at the Earth's surface at this time ranges from less than 30 microtesla (0.3 gauss) in an area including most of South America and South Africa to over 60 microtesla (0.6 gauss) around the magnetic poles in northern Canada and south of Australia, and in part of Siberia.

The field is similar to that of a bar magnet, but this similarity is superficial. The magnetic field of a bar magnet, or any other type of permanent magnet, is created by the coordinated motions of electrons (negatively charged particles) within iron atoms. The Earth's core, however, is hotter than 1043 K, the temperature at which the orientations of electron orbits within iron become randomized. Such randomization tends to cause the substance to lose its magnetic field. Therefore the Earth's magnetic field is caused not by magnetised iron deposits, but mostly by electric currents (known as telluric currents).

...cont'd

http://www.crystalinks.com/magnetics.html
-----------------------------------------------------

DEPLETION OF THE EARTH'S MAGNETIC FIELD
- IMPACT No. 100 October 1981
by Dr. Thomas G. Barnes

© Copyright 2004 Institute for Creation Research. All Rights Reserved.

There are three important force fields associated with planet earth, a gravitational field, an electric field, and a magnetic field. The gravitational field attracts us to the earth, preventing us from flying off into space as the earth rotates. The earth's electric field is very unstable, producing electric storms from place to place and at unpredictable times.

The earth's magnetic field is due to a huge electric, current, billions of amperes, circulating in the core of the earth. But the main complication lies in the fact that there are a multitude of extraneous sources which produce distortions in the magnetic field. As a consequence, the earth's magnetic field is very complex. The instability sometimes shows up as tremendous magnetic storms, blocking out transoceanic radio transmissions. There are all kinds of anomalies resulting from distortions in the magnetic field. There are many unpredictable variations in the magnetic field with time and location.

Navigators do not depend on their magnetic compass as much now as in early days. When navigators do use the magnetic compass they have up-dated magnetic charts to provide corrections for gross deviations in the earth's magnetic field from place to place over the globe. This helps them correct their bearings for "false" directions indicated by the compass, but the charts can not correct for all the distortions.

...cont'd

http://www.icr.org/pubs/imp/imp-100.htm

[Nihil]

6. Thanks (n/t)