Fig. 1 Picture of Iwate-san volcano
Taken from Matsuo Village north of the volcano in 1987.
Fig.2 Total intensity magnetic anomaly map of Iwate-san volcano (Okuma, 1998)
Contour interval is 20 nT. H and L denote a magnetic high and low, respectively. The map area corresponds to the box bounded by blue lines in Fig. 1 at the home page of the Sengan Geothermal Area. Topographic maps of Hachimantai, Numakunai, Shizukuishi and Morioka on a scale of 1: 50,000 (GSI) were employed.
Fig.3 Apparent magnetization intensity map of Iwate-san Volcano (Okuma, 1998)
Contour interval is 20 x 10 -2 (A/m). H and L denote a magnetization high and low, respectively. See also Fig. 2.
(1) Generally, magnetization highs
lie around the edifice of Iwate-san volcano, suggesting the existence
of magnetic volcanic rocks.
(2) However, magnetization lows are distributed in the western
crater and on the western parts of the edifice: Inukura-yama,
Kamakura-mori and the area above Iwate-Kogen ski resort (red arrow in Fig. 3). These magnetization lows correspond
to a hot spring, Amihari-motoyu, below Inukura-yama, and old craters
which produced the Amihari Volcanic Rocks (Doi, 1991), suggesting
demagnetized areas of the edifice caused by hydrothermal activities.
(3) Earthquakes associated with the recent volcanic activity are
distributed mainly on the areas of magnetization highs north of
the magnetization lows mentioned above (2), implying that they
occurred in less hydrothermally altered areas.
(4) A sharp boundary of magnetization intensities exists on the
eastern flank east-north-east of the summit of the volcano, suggesting
a relationship with craters of the Yakebashiri Lava Flow (black
arrow).
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