Open Access

Magnetization intensity mapping on Unzen Volcano, Japan, determined from high-resolution, low-altitude helicopter-borne aeromagnetic survey

  • Ayako Okubo17Email author,
  • Yoshikazu Tanaka27,
  • Mitsuru Utsugi27,
  • Naoto Kitada27,
  • Hiroshi Shimizu37 and
  • Takeshi Matsushima37
Earth, Planets and Space201457:BF03351853

https://doi.org/10.1186/BF03351853

Received: 29 January 2004

Accepted: 12 July 2004

Published: 20 June 2014

Abstract

On September 18, 2002, we conducted a high-resolution, low-altitude helicopter-borne aeromagnetic survey at two flight altitudes, using spiral trajectories for the first time, over Unzen Volcano in the framework of the Unzen Scientific Drilling Project (USDP). This study obtained more detailed and new information than the previous aeromagnetic studies in Unzen volcano about the geological features, for understanding the history and eruption mechanism of the Unzen volcano. Therefore, we conducted a magnetization intensity mapping on the volcano, on the assumption that the magnetic anomalies are caused by the terrain magnetized in the same direction as the present Earth’s magnetic field and the magnetization intensity varies only laterally. This map shows good agreement with the geologic features, especially the hydrothermal alteration zone and the collapsed pyroclastic deposits. In addition, even in the area covered by lavas, the magnetization intensities show various values corresponding to each eruption event. It may be considered that the differences in magnetic properties reflect different oxygen fugacity in rocks during their cooling time period. Local magnetization lows on Heisei-Shinzan suggest that the Heisei lava produced by the 1991–1995 eruption has not yet been cooled enough.

Key words

Aeromagnetic survey Unzen volcano magnetization intensity mapping