Large-Scale Motions: How and Why? We have been discussing volcanoes, earthquakes and other geophysical activity, which we can visualise as being on scales which can be described as local. We speak, for example, about an 'earthquake in Japan', and know about Mt Etna in Sicily. But there are truly large-scale motions that lead to a constant steady reworking of the distribution of large plates that make up the surface of the Earth, rather like gigantic pieces of a jig-saw puzzle that are free to slide around. Just to be specific in the ensuing discussion, I will ask you to imagine North America slowly moving away from Europe, but please note that this behaviour is not restricted to this one example. Moreover, please note the following very important qualification: in general, the plates do not correspond to specific continents.
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