MadSci Network: Earth Sciences

Re: If the earth's magnetic poles DO reverse will the earth flood?

Date: Tue May 18 14:18:59 2004
Posted By: Peter Thejll, Staff, Solar-Terrestrial Physics, Danish Meteorological Institute
Area of science: Earth Sciences
ID: 1084905328.Es

The Earth has magnetic poles because of things happening in the interior 
of the planet. Some process in there maintains a magnetic field, and it 
is clear from measurements of the strength of the magnetic field on the 
surface - where we live - that processes inside the Earth are variable. 

This causes the magnetic field to vary in strength and indeed in 
direction. The poles 'wander', and magnetic North is not in the same 
place all the time. Right now North is a place West of Greenland, in 
Canada. At other times the magnetic pole has been where the Geographic 
pole is and at other times the polarity has been reversed so that 
magnetic North was South. 

From measurements of the magnetic field in rocks it is possible to 
measure the strength and direction of the Earth's magnetic field at the 
time the rock formed. In this way it has been possible to map the Earth's 
magnetic field back in time, and it seems that at certain intervals the 
field completely dissapears and then comes back with opposite polarity.

Careful measurements of the Earth's magnetic field over the last 100 
years or so have shown that the field strength is declining. IF it 
continues to do so it might indeed be gone in a relatively short time 
(perhaps the number is something like a few hundred or thousands of years 
from now). After a time it will probably come back, perhaps with opposite 
polarity. Then again, perhaps it will not decline in strength but instead 
pick up strength. Science doesn't know yet.

So, what is the possible effect of such reversals and dissapearances of 
the magnetic field on rivers and oceans? Well, as far as we know, the 
effect is very little or absent. The reason is that the magnetic field 
does not have a grip on the oceans or rivers to any very large extent. It 
is in fact true that there is a little interaction - let me explain. With 
very sensitive instruments placed on Greenland it is possible to measure 
the effect of ocean currents nearby. This is because the oceans are 
partial electrical conductors and as the ocean currents move water along 
there is a small induced electric current and a weak magnetic field is 
formed that can be measured onshore - it is in fact possible to see how 
fast the ocean is streaming past the coast using magnetic data from 
nearby stations. Now, the opposite is also possible - with a variable 
magnetic field it might be possible to move the oceans about - a bit - 
and the same with rivers. 

However, the 'grip' of magnetic fields on oceans and rivers is very very 
VERY small. If you turned the fields off - like they pretend in the 
movies - absolutely NOTHING would happen. Perhaps ocean levels somewhere 
would change by as much as the thickness of a sheet of paper, or less. No 
huge sloshing oceans storming onto coasts in other words. No rivers 
running backwards or anything exciting.

Also, such field turn-offs and reversals have, as I mentioned, happend 
many times before, and there are no signs of major catastrophies 
happening at the same times.

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