The “Green Tuff” region is defined as existence of abundant submarine volcanic rocks of Early Miocene and overlying oil-bearing pelitic clastic sediments of Late Miocene-Pliocene age. The region, which covers the western half of the Tohoku District in Northern Japan, is also characterized by predominant distribution of Tertiary landslides recognized by interpretation through aerophotographs.
In this entire region, reserches on the relations between geological and geomorphological conditions and the distribution of landslides are very few. In this paper, the features of Tertiary landslides distribution are especially discussed from geological and geomorphological point of view.
The areas of high distribution density of the landslides coincide with the areas where rapid upheaval movement occured during the Quaternary age. Geologically, a large number of the landslides occured in the areas dominated mainly by mudstone and tuff, and in the areas where has been intensively folded since Late Pliocene age.
It is a remarkable fact that the distribution pattern of the landslides is conformable with the characteristics of the late Cenozoic crustal movements. This suggests that the occurrence of the landslides is based on the tectonic history, specifically on its latest one of the region. Problems on prediction of landslides should be considered from such a point view.

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From a geological and geomorphological point of view, the writer described some landslide areas in Hokuriku district, especialy the Hime Kawa River basin, and on the hilly districts in Boso Peninsula, and pointed out their characters.
The one is an active landslide of high velosity which has not typical landslide topography, and caused by a certain character of the geological structures which consist of the Mesozoic and the Palaeozoic rock formations. This kind of often causes a great deal of damage.
The other occurs at areas with the Tertialy pelitic rock formations and the Qurterary volcanic deposits, and exhibits a continuous landslide movements, which is not so violent as to cause damege to people and houses. However, a gigantic landslide occur at the Qurtanary volcanic deposits areas at times.

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I review rapid deep-seated landslides which took place in Hokkaido. Such landslides are giant rockfalls and rapid rockslides, as follows. The Ainuma-Toyohama coast facing Japan Sea, southern Hokkaido, is characterized by the following three landslides ; Toyohama Slide on Oct. 17, 1962 ; Orito Slide on December 20, 1985, and Tachimachi-misaki Slide on August 9, 1991. The Orito Slide and Tachimachi-misaki Slide are primary dip-slipping slides. While, the Toyohama Slide was secondary slipping from the toe of an ancient slide, killing 14 passengers with a bus. Kodomari Slide occurred on April 17, 1978, and blocked the main road for a month. Tenninkyou Rock Slide occurred on October 16, 1980, and crushed a rock shade, and the debris went over the Chubetsu River injuring 4 persons by attacking a hotel. Sounkyou Rockfall took place on June 9, 1987. Many long collumns of welded tuff fell down and the debris went over the Ishikari River, killing three people including truck drivers. Okushiri Port Slide took place on July 12, 1993, induced by Hokkaido Nanseioki Earthquake (M=7.8), southern Hokkaido. This is a rock slide which crushed a hotel and 29 people were killed. Toyohama Tunnel was crushed by giant rockfalls, killing 20 people who were just running by a bus and car on February 10, 1996.
In conclusion, for the landslides mentioned above, I emphasize the importance of vertical and horizontal discontinuity, intercalation of clayey tuffs, cooling joints and caprock structure in view point of geology. I also point out that such landslides were triggered by a certain preceding precipitation, increase of under-ground-water pressure and earthquakes.

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An example of unexpected landslide in crystalline schist is reported. After conventional investigation; such as a survey of ground surface, boring and ground water survey; a hill is cut partially at its toe to construct a new road. The degree of the cut slope was very low to maintain the slope stability. Then a landslide occurred after heavy rainfall. Additional surveys; thus, boring, standard penetration tests, and measuring by pipe strain meter and extensometer, were conducted. The shape of landslide was identified by means of these surveys. After considering several countermeasures to prevent landslide, earth removal work was selected, which stabilized the landslide. We propose an idea that new knowledge about unexpected landslide will be obtained by selecting a characteristic common to many landslides that occurred at various geological features and underground water level in Japan.

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Slope failures induced by earthquakes were divided into five types: the steep slope, the intermediate layer, the liquefaction, the ground water and the artificial slope. The steep slope type is the most common type of earthquake-induced slope failure. The prediction method of this type which is judged from rock hardness (interfriction angle and cohesion) and slope angles was already reported. A number of the intermediate layer type were happened on gentle slopes. They were usually large in size and the most dangerous type on the disaster prevention. It has been pointed out that the cause of this type was the failure of white tuff or pumice layer. The phenomena of the liquefaction and the ground water type are not clear, so the prediction method is the problem which should be solved in the future. When the disaster prevention of cities is considered, the artificial slope type must be a big problem. But the study is not enough.

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Unlike rain, snow tends to accumulate and remain on the ground, melting over time. To better predict the occurrence of landslides during the snow cover season, it is necessary to make an accurate estimate of the timing and intensity of meltwater flowing out from the bottom of a snow pack. Although meltwater can be estimated by the degree-day or heat balance methods in the snowmelt season, it is difficult to estimate the melt water in the early period of the snow pack season and when rain falls on an accumulated snow. This is due to the complicated nature of the heat balance compared to the snowmelt season and to unknown variables such as the water-holding capacity of the snow cover. At the same time, the water equivalent of a snow pack is believed to affect slope stability in terms of load and glide. However, the details of these mechanisms are not clear due to the uneven distribution of snow and the complex interrelationships between the snow load and the sliding and ground surfaces. Compounding this is the relation between pore water variation and slope stability, which is difficult to ascertain due to repetitive loading and unloading.

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