Impact on the Electric Infrastructure Due to Volcanic Ash from a Hydrovolcanic Eruption of Aso Volcano in 2016

A hydrovolcanic eruption in the early hours of October 8, 2016 triggered a power outage of about 29,000 houses (similar to 50,000 habitants) in the Aso caldera area, Kyushu, Japan. Although it was recovered naturally by the early morning of that day, the power outage occurred again in the evening following rainfall that began in the afternoon. The power supply in the caldera area had been temporarily maintained despite the heavy landslide damage due to strong earthquakes in April 2016, without the supplemental transmission lines for the normal standard. The power outage is considered to have been due to the insulator flashover in the power substation, Ichinomiya, Aso, around which the mass of volcanic ash was about 3,000 g/m(2) or less (<= 3 mm thick). This outage resulted from high electric conductivity of the volcanic ash that was wetted with strongly acidic water dammed in the crater before the eruption. This may be one example of the power outage incident due to thin ash fall.