Magnetic measurements of roadside topsoil pollution in an active volcanic region: Mt. Hakusan, Japan

Environmental magnetic applications to topsoil have proved useful for investigating roadside pollution. However, such magnetic monitoring has been avoided in volcanic regions due to the high magnetic content in volcanic ash. Environmental magnetic studies are reported for the volcanically active Mt. Hakusan National Park in Japan. In-field magnetic susceptibility measurements along the park's major road show higher magnetic susceptibilities in topsoils within 1.5 m from the roadside. However, laboratory mass susceptibility measurements fail to show a similar susceptibility trend to the field measurements. Based on rock magnetic analyses, the major magnetic mineral is pseudosingle- to multidomain (MD) magnetite that is both increased in abundance in MD and oxidized magnetite near the roadside, indicating that passing vehicles are evidently the main pollutant source. Therefore, even in an active volcanic region where magnetic susceptibility may not be an efficient tool, detailed magnetic measurements can provide the basis for the discrimination of roadside pollution.