Problems in Determination of the Beginning of the Bandai-san Eruption in 1888

Abstract

On the 15 th of July 1888, a terrible eruption took place at the Bandai-san Volcano in northeastern Japan. Although many articles concerning that eruption were published during the last century, there are still some unsolved questions. The authors tried to solve some of them, including the uncertain situation of determining the beginning of that eruption. They found and examined some previously undiscovered data and the evidence of eyewitnesses. The results are as follows;1. Time: The eruption started at 7:45 a. m., 15th of July 1888 (Sekiya·Kikuchi 1890). But many eyewitnesses stated that it was between 8:00 and 8:10 or around 8:30. The disagreements in time are presumably caused by confusion on methods of hour system. The year 1888 fell into the transitional period between three kinds of hours or times: the temporal hour (-1872), the equinoctial hour with local time (1873-1887), and the equinoctial hour with Japanese Standard Time (1888-).2. Sites: The sites of the first explosions are inferred to be on the western foot of the peak of Kobandai and near Akanuma Pond, from photographs and sketches made by some residents at the foot of Bandai-san during the eruption.3. Height of eruption column: The height of eruption columns during the first explosion was estimated to be only 800m from the sketches and other evidence. This fact supports Moriya's opinion (1980) and Yonechi's hypothesis (1987) that the first explosion of Bandai-san had been not so big, but the following collapse (-s?) was (were?) much larger.