シラス ノ ドシツ リキガクテキ トクセイ ト ソノ ゲンイン : シラス ボウサイ ノ ケンキュウ ダイ一ブ ソノ2

In this paper, the author tried to summerize the history of studies of "Shirasu", which, he thinks, reveals itself through the relation. And he attempted to divide the time into three periods. The first, preparatory, the second, of fundamental research, and the last, which may be subdivided into two parts, is of florescence. The first or preparatory period will be the time before people suffered the great damage from typhoons Dela etc. hit the South Kyushu district in the summer 1949. The second period appears to be until the end of 1961, when the regulating law of building-land-making was published. The last, from that time down to this day. Here the auther writes till end of the second period. Through the first period we have various kinds of research, concerning natural science, engineering, disaster, and agriculture. Among the rest, reports on geological matter are remarkable. Especially T. Matsumoto's works about sunken calderas in South Kyushu are most prominent and famous. He assumes that other three gigantic volcanic calderas of the Aso type existed in South Kyushu and he named two of them Aira and Ata calderas. "Shirasu" and mud-lava are similar in substance comming from the above two past volcanoes.R. Nishi reported about the forms of landslips in the experimental plantation of Kagoshima Higher Agricultural and Foresty School. Though he did not just notice “Shirasu” of its distinct properties, the report is yet noteworthy having not little to do with it. Generally speaking, they did, of course, not imagine the subsequent disaster and also did not pay attention to "Shirasu" as the cause of it during that time. In 1949 big typhoons as Dela hit South Kyushu and brought much damage. They became aware that "Shirasu" had much to do with landslip and outflow of sand, and more over, that is was the chief factor of the disaster. Research and investigation became active. Many reports were made public. The auther now picks up most representative two individual works and gives rough introduction of them. G. Miki's study of "Shirasu" chiefly from the field of soil mechanics was the first authoritative work and became a firm base of followers. After general observation of natural "Shirasu" and its tableland he found out some charactaristics of it. For example, (1) water erosion is conspicuous, and he noticed the covering effect of the uppermost pumice-loam bed, (2) a slope stands high safely upright, (3) mechanical properties change when disturbed, and (4) the essential means of preventing a landslide are to protect "Shirasu" from water flow, were what he uttered. Carring out various tests as compression test both of disturbed and undisturbed test pleces, bending, compaction, penetration, permeability, and water erosion of mixed material of "Shirasu" with pumice-loam, he gave ground to the above utterance and showed some practical ways how to treat natural "Shirasu" and its disturbed soil.One important matter, however, remained unsolved, that is the stability of a high steep cliff. Miki attributes the cause to internal friction, but it is rather difficult to accept. After carefully observed the damage cite M. Tamachi offered several concluding remarks of actural use. He thought, regarding the upright cliff, a certain unknow cohesive power such as from chemical substance or of natural welding would exist. His proposal, widely covering the field of agricultural civil engineering and others, overlaps much on Miki's opinion and well agrees with it except the stability theory. He classified the types of landslide according to the causes, which many followers rely upon. Treating technics of water both on the tableland and underground and the devices for the "Shirasu" dam work are suggested. His contribution to those branches is estimable. We can find not a little papers and data in the fields of engineering or geological science. R. Nishi cooperated with D. Kimura to know water erosion by actual test. S. Taneda doubted that “Shirasu” is "aqueous deposition" of ejecta hurled up far from the vents and made it plain of its being pumice-flow. M. Minato amd Y. Katsui stratigrafically investigated the "Shirasu" of Aira caldera and Y. Gohara with K. Komori also arranged the strata of those of Aira and Ata calderas. Thus fundamental research was almost established before the end of this second period, 1961