Variations of iodine isotopic ratio in hydrothermal system and volcanic activity at Zao volcano
Matsunaka, Tetsuya*; Goto, Akio*; Watanabe, Takahiro ; Tsuchiya, Noriyoshi*; Sasa, Kimikazu*
The volcanic activity has become higher at Zao volcano in Japan since January 2013 after the 2011 Tohoku Earthquake. Basic water quality of crater lake and geothermal area have been studied by Tohoku University since the water quality of hydrothermal system in volcano are correlating with volcanic activity. As a part of this investigation, we are trying to monitor the volcanic activity using iodine isotopic ratios at Zao volcano. In our previous study, iodine isotopic ratio in water collected in October 2013 from the crater lake at Zao volcano were 2.210, which were affected by anthropogenic I. In terms of the global iodine cycle, chronologically-old iodine with low isotopic ratio was considered to be supplied into the crater lake and geothermal area from underground corresponding to the volcanic activity, resulting the decrease in iodine isotopic ratio of the crater lake. The iodine isotopic ratios of the crater lake increased from 2.210 to 5.610 during October 2013 to the middle of October 2014, then, abruptly decreased to 4.310 soon after the white turbidity in the lake. While the iodine isotopic ratios of the geothermal area decreased from 5.310 to 1.610 at August 2014 corresponding to increase of the volcanic earthquake. Further investigations are needed to discuss the relationship of changes in iodine isotopic ratio of the hydrothermal system and the volcanic activity at Zao volcano.