Behavior of Magnetic Particles in Snow and Ice Involving Volcanic Ashes

Aritificial snow samples for these experiments were made by mixing sorted snow grains and fine magnetic minerals. Dry dirt-snows acquired NRM toward the geomagnetic field(GMF) direction, although the NRM direction shifted toward flat maintaining northward declination after several days. It seems to be an important fact to explain the mechanisms of NRM acquisition that the metamorphism of snow set fine magnetic particles free. Then the magnetization of particles tend to turn toward GMF direction and stick to another parts of snow grains. In the case of dry snow samples, metanorphism of snow is made progress by the sintering of snow grains. In the process of moving of H_2O molecules to the narrow part, many magnetic particles free itself from the surface of snow grains, and may turn to the GMF direction. These particles collect on the narrow part or the grain boundaries and have fixed directions of NRM in the course of time. In the case of wet snows involving magnetic particles, they have thin water layer on the surface of snow grains. Therefore it is not difficult to set the magnetic particles free and to acquire the NRM when the melt water refreezed. Microscope observations of the dirt-snows thin sections proved that the NRM was acquired when the metanorphism of snows developed.