@article{oai:niigata-u.repo.nii.ac.jp:00028172,
 author = {藤田, 至則},
 journal = {新潟大学積雪地域災害研究センター研究年報, 新潟大学積雪地域災害研究センター研究年報},
 month = {Jan},
 note = {Mass-movement is a general term for disasters in the mountains and hilly lands, such as falls, slides and flow (TAKEI, 1980). It has been revealed that these phenomena were repeated since geologic times. Occurrence of the so-called primary mass-movement to be generated in the virgin areas of mountains and hills is scarce at the present time, but it must have taken place during a certain geologic age on a large scale in both number and quantity, and it is called today a buried mass-movement or palaeo-mass-movement. The mass-movement currently taking place is generally believed to be a regenerated mass-movement of the primary one for the most part. Therefore, the study of the palaeo-mass-movement is important for clarifying the materials of the present mass-movement as well as for investigating its generation mechanism. On the origin of the palaeo-mass-movement, the writer has reached a conclusion that the upheaval-collapse movement which was repeated five or six times in the Island-arc disturbance since the Pliocene time was the major cause of the palaeo-mass-movement In this paper, the factors controlling the formative process of the palaeo-mass-movement are analyzed to corroborate the above view. The writer has previously mentioned that the mountainland upheaval, the increased difference in the relative altitudes of landforms due to the sea-level fall during the glacial epoch, and the supply of great quantities of groundwater in the region of heavy snowfall resulting from the climatic changes on account of the warming of the Japan Sea about 8,000 to 10,000 YBP, are the factors that determined the large scale palaeo-landslides (FUJITA, 1981 a, b). For example, the concentration of palaeo-landslides of 70,000-150,000 YBP and 20,000-30,000 YBP is undoubtedly owing to the glacial eustasy, and that of 6,000-10,000 YBP is attributable to the appearance of the heavy snowfall region on the Japan Sea side. Nevertheless, the writer considers that the decisive factor of palaeo-landlide is the action of gravity in the course of upheaval, judging from the analytical results of the above-mentioned Island-arc disturbance and from the results of the following analysis., 1. According to the recent researches, occurrence of primary mass-movement, that is, palaeo-mass-movement of a large scale, concentrated in five periods, namely, 5,000-6,000 YBP, 8,000-10,000 YBP, 20,000-30,000 YBP, 70,000-150,000 YBP and 200,000-300,000 YBP (Fig 5). As these periods correspond to the terrace-forming stages in the latter half of the Quaternary, it would be reasonable to ascribe the cause of paleo-mass-movement to the events related to the formation of mountains and hills. 2. Typical terraces in the Japanese Islands were formed since about　500,000 YBP, and it is a matter of course that the palaeo-mass一movement on land took place later than that. By the way, the greater part of the palaeo-mass-movement that occurred in the early stages of the Island-arc disturbance during the first half of the Quaternary was of aqueous deposit. 3. The land upheaval proceeding in the terrace-forming stages would bring about accumulation of stress at a certain point, and as the accumulation exceeds the limit, the stress would be released and shatter the hard part of the crust, and consequently the overlying soft crust would be deformed by flexure. This should serve as a momentum for creating new terrace surfaces. 4. The absolute age of the stress-accumulating stage has been mechanically obtained, with the result as shown in Fig. 5. In the figure we can see that the period of stress accumulation in younger age is shorter than that for an older one. This tendency agrees with what was pointed out by HUJITA, K. (1976) that the speed of the Quaternary disturbance gained with age. Although there is a view that the deformation speed in the Quaternary did not change (SUGIMURA, A. 1967), it concerns only with the tendency of a short period of time. 5. It is possible that the release of stress in the manner of flexure or fault took place not only along the boundary between younger and older terraces but also in the mountains and hills at the back of the terraces. The appearance of new landforms such as terraces, mountains and hills of different altitudes must have accelerated the generation of palaeo-mass-movement in great quantities., 6. As indicated in Fig. 2, 3 it can be said by experience that a primary mass-movement is much larger in quantitative scale than a regenerated mass-movement, but no accurate researches have been made as yet. Nevertheless, it is inferred that the great quantities of mass-movement in the past had occurred during the period from 500,000 YBP, when the amount of upheaval of the mountains and hills began to increase rapidly, to the present time, or, in the context of what has been mentioned before, a certain age after 500,000 YBP. 7. Most of mass-movement occurring in the Japanese Islands of the high-rain belt are considered to be regenerated palaeo-mass-movement, since water, oscillation and operation would act as an inducing factor to regenerate some unstable ones among the numerous palaeo-mass-movement. Whether or not the stress releast due to upheaval is causing the current mass-movement must be checked from a historical standpoint, so that it is difficult to get hold of, or to predict, the occurrence of mass-movement by means of the present-day analysis. It is true, however, that the primary mass-movement is actually occurring though on rare occasions (refer to Fig. 4). 8. The so-called primary mass-movement, of the present time or in the past, must have occurred on account of the topographic difference produced by the sudden release of stress which was accumulated by the progressing upheaval and was concentrated in the portions of ancient fault or facies transition. In other words the energy at the position created by the altitudinal difference of landforms has stimulated the generation of mass-movement. This means that the upheaving movement seldom worked as the trigger for mass-movement.},
 pages = {39--51},
 title = {Mass-movementの起源},
 volume = {6},
 year = {1985}
}