Topography and geology of the midstream area of the Hime valley is fairly complicated, and there are abundant groundwater caused by heavy snowfalls of this area.
There can be seen many gently slanting surfaces in the arrea; the writers investigated these gentle slopes topographycally, geologically and genetically.
The sloping surfaces are classified into 1) old erosion surface 2) slope caused by landslip of pyroclastics 3) slope caused by Tertiary landslide 4) fluvial terrace and so on Therefore, many of them have some relation to landslide in broad sense.
The gentle slopes of Tertiary landslide are concentrated in areas of alternated mudstone and sandstone, and they are closely related to geologic structure. The writers reexamined the genesis of many gentle slopes along the Hime river which have been considered to be fluvial terraces so far. The study on gentle slanting surface in landslide area will be effective for both prediction and counter measure of landslide.

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It is very important to predict the landslide behaviour in prior to its occurence, especially for the traffic safety. The authers measured the landslide movement and groundwater table variation in a landslide between Toyono and Mure on Shin-etsu line. The measured data show that after water tables in the landslide area keep high level during long period in snow melting or rainy season the distinct landslide movements occur.

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Recentry, slope failures caused by heavy rainfall occured at Noboribetsu City.
During August 28 to 31, 1980, the total precipitation reached 576mm and maximum rainfall intensity attained 60mm/h at 6: 00 a.m. on August 31, recorded at Horobetsu town along the coastal area. This rainfall pattern was the coast rain. Most of the slope failuers were concentrated in the area from Horobetsu to Tomiura, where the precipitation of 40 to 60mm/h associated with previous rainfall 200mm, was documented.
In September 24 to 25, 1983, the total precipitation reached 508mm and rainfall intensity attained 126 mm/h at 4: 00 a.m. on September 25 at Satsunai. This rainfall pattern was the hill rain. The numerous slope failures, debris flows and erosion of river bottoms occured in the area from Mt. Kamuinupuri and Satsunai hill to Lake Kuttara, where the precipitation of 250 to 300mm without previous rainfall.

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