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Pumice fragments that were emitted in the 1985 eruption of Nevado del Ruiz volcano (Colombia) display a rarely observed type of magnetic reversal, according to a paper in the November 20, 1986, issue of Nature. This pumice seems to have undergone self-reversal, according to the paper's authors; it is the first example of newly formed rock with a magnetization opposite to that of the earth's present field.