Resumen de Evidencia de un fenómeno de autoinversión de la NMR en piroclastos de la erupción de 1985 del volcán Nevado del Ruiz (Colombia)
Juan Carlos Carracedo Gómez, F. Heller, Vicente Soler Javaloyes
During the catastrophic 13 November 1985 eruption of the Nevado del Ruiz volcano (Colombia), that caused the death of 25000 people and damages assessed at US$ 300 million, severa! types of pyroclastics were emitted including incandescent fragments of andesitic pumice. Oriented samples collected by one of the authors (J.C.C.) from pumice fragments embedded in the ground due to the force of impact contradict one of the fundamental principies of palaeomagnetism that states that the direction of natural remanent magnetization (NRM) is acquired parallel to the applied field. lndeed, these pumice samples carry a stable NRM, but antiparallel to the present geomagnetic field. This fact has been shown to be due to a phenomenon of self-reversal that controls the process. of NRM acquisition and is recorded for the first time on this occasion and reproduced in thermal experiments in the laboratory.
