|MadSci Network: Earth Sciences|
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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