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Books on Devon UK (Amazon.com) Books on Devon UK (Amazon.co.uk) Copyright Peter Thomson 2005 | ||
Evidence from the coast of Devon Looking for the Ice Age Shore Line Magnetic Reversals and Crustal Overturn Evidence from the coast of Devon |
Magnetic Reversals and Crustal OverturnThe Earth's magnetic field periodically changes, but no theory effectively explains why or when this happens. Crustal overturn could provide part of this answer, and also help calculate the thickness of the crust that moves. If the magnetic field is produced by the earth's core, the most likely location, it is very unlikely that whatever mechanism produces it that it is going to flip! The core is simply too massive. The Earth's core produces a powerful magnetic field, and this will induce an aligned magnetic field in the crust. This will align any magnetic domains in the crust with the internal field and will form a permanent magnet, producing a crustal magnetic field aligned with the internal field. When the crust overturns, the permananet magnetic field of the crust is no longer aligned with the internal magnetic field, and now shields the internal field from the core. The magnetic field on the outer surface of the crust reflects the crustal field, so there is no immediate magnetic flip from the crustal overturn. Instead, the internal magnetic field will slowly re-align the crustal field. As the crustal field loses its strength in its original orientation, the process of realignment will accelerate. This realignment process will not be uniform over the Earth's surface. As the internal field comes to predominate at the surface in one region, a new north and south pole will appear at the surface in that region. For a time there will be multiple north and south poles scattered over the Earth's surface. The Earth's magnetic field will not decay to zero and reform in the opposite direction! Regions showing the current crustal N-S alignment will shrink in size as regions showing the new S-N alignment grow. These multiple poles will appear to drift towards the axis of rotation poles, until the magnetic field becomes uniform with an opposite polarity to that of the present, and a magnetic flip will have taken place. The magnetic flip will be complete when the internal magnetic field has induced a matching field in the crust, but because the two fields will be in alignment, the total magnetic field will be much stronger than it is now. This theory also explains why the present crustal magnetic field is centred over northern Canada, some distance from the present geographic pole. When the crustal and core magnetic fields are in equilibrium the magnetic pole and the rotational pole should be in alignment. The difference between the two at present is a measure of how much the crust shifted in the last crustal overturn. This information is copyright Peter Thomson 2001-2004 The following files on this site match your querySearch for any topic in this forumMore pages or to contribute to the discussion- look at the list in the main index.
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