Reconstruction of the Landform of the Peaks of Mt. Kobandai and the Eruption of 1888 interpreted from Old Sketches

Abstract

In geomorphological analysis, scholars generally have at their disposal geological date much more useful than pictorial records. Yet pictures are potentially rich sources of information about past visual representations of landforms.
In this paper the author intends to encourage greater use of pictures. He used two kinds of pictures for the study of Mt. Kobandai, one of the Bandai-san Volcanoes, which erupted and vanished on 15th July 1888.
One are skethes of the Bandai Volcano made during the 1888 eruption by local eyewitnesses. The author presents two newly-found sketches (Fig. 1, 2) as evidence of his “plural collapses hypothesis” (Yonechi 1987) of the 1888 eruption of the Bandai-san Volcano. During the past century, most scholarly articles were based on the assumption that a violent steam-blast eruption destroyed the peak of Kobandai just after the first eruption. However, the author's hypothesis claims that the disaster was composed of at least two collapses, large scale destruction in the first stage which occurred on the mountainside, and the gigantic collapse of the peak of Kobandai in the third stage following a lull (the second stage). His argument is based on the presentation of two photographs and two series of sketches, “Bandai-mura Ser. or Otomo Ser.” and “Kobayashi-printing Ser.” In this paper he presents two pieces of supplementary evidence, “Nitta drawing (Fig. 1)” and “Kobayashi-handwriting Ser. (Fig. 2)”.
Another kind of picture is “shin-kei zu” (literally “real landscape drawings”) by painters. The author found some sketches depicting the shape of Mt. Kobandai before the 1888 eruption in this “shin-kei zu” technique. They are Koson Endo's sketch in “Shinyu-kiko zue” (Fig. 4) and Haku-un's in “Iwaki-kiko zukan” (Fig. 5).
From these pictures and already-known pictures by Hokai Takashima (Fig. 6-8), the author made a 3-D model (Fig. 9). It shows that the vanished Mt. Kobandai had two peaks, and each of them had two small bulges.
Mt. Kobandai as represented in the 3-D model has a rugged shape different from the photographs taken during the eruption, which show a smoothly-sloping profile. The author presumes that a part of Kobandai's peak collapsed during the first stage of the eruption at almost the same time as the mountainside collapse. He concludes that his hypothesis is supported on the whole and modifies it slightly to add a relatively small collapse of a part of Mt. Kobandai's peak in first stage of the eruption.