STUDIES ON GEOMORPHIC POSITION AND TIMING OF REGOLITH SLIDE OCCURRENCE

通过野外和实验室水文地貌和土壤地貌观测，获得了降雨引起的风化层滑坡发生的地貌位置和时间。主要研究结果如下：1）在日本东北部的仙台地区，土壤蠕变是坡体上部风化层移动的主要过程。它的速度从每年0厘米到几厘米不等。在每年雨季和积雪异常时的融雪期，在填充基岩空洞的土层/层中记录了相对较大的速率。B或BC层位表现为块体型运动，而A层位则以流动型运动为主。在斜坡基岩面上的B或BC层的轻微滑动似乎引起上覆A层的土壤颗粒流动。2）在下部斜坡段，通常厚度小于1 m的风化层由上部斜坡段通过上述过程提供， ...更多信息 即快速下滑，大多数情况下一个场地的体积小于1,000 m^3，下滑频率为几百年。降雨量在几百毫米到几十毫米之间，降雨强度在35毫米/小时左右，可引起仙台周围丘陵地区的土壤滑坡，导致管流在几个土层迅速增加。3）管流最活跃的土层是B层或BC层。管流流量在各个土壤层/层和其份额的变化，响应降雨强度和持续时间。管流在多个层位/层位上的变化响应取决于O和A层位处的高渗透率和B或BC层位处的大存储容量。4）更强的降雨可以在斜坡的上部段（主要是最顶端的壁）诱发风化物滑动，特别是在具有厚腐岩和高起伏的丘陵中。这似乎是由于浓缩水集中在管道上，这些管道的出口在上部，在弱雨的情况下不起作用。少

Hydrogeomorphological and pedogeomorphological observations were carried out both in the fields and In the laboratory in order to obtain the knowledge on geomorphic position and timing of the occurrence of rain-induced regolith slides. The major results are as follows:1) Soil creep is the major process of regolith movement on the upper slope segments in the hills around Sendai, northeastern Japan. Its rate ranges from 0 to several centimeters per year. Relatively great rate is recorded at the soil horizons/layers which fill bedrock hollows in rainy season every year and snow-melt periods in the case of extraordinary snow accumulation. B or BC horizon shows block type movement while flow type movement prevails in A horizon. Minor slide of B or BC horizon on sloping bedrock surface seems to induce flow of soil particles in overlying A horizon.2) On the lower slope segments, the regolith, which is usually less than 1m thick and provided from the upper slope segments by the process as abov … More e, rapidly slides down with the volume of less than 1,000m^3 at a site in most case and the frequency of several hundred years. Rain which can induce regolith slides in the hills around Sendai is more than hundred and several tens of millimeters in total and about 35 mm/h in intensity, which leads to rapid increase of pipe flow st several soil horizons/layers3) Most active pipe flow occurs at B or BC horizon. Pipe flow discharge at respective soil horizons/layers and its share changes in response to intensity and duration of rainfall. The changing response of pipe flow at several horizons/layers depends on high percolation rate at O and A horizon and large storage capacity at B or BC horizon.4) More intense rainfall can induce regolith slides on the upper slope segments, mostly the headmost walls, also, particularly in the hills with thick saprolite and high relief. It seems to be due to concentration of percolated water to the pipes which have their outlets on the upper part and are inactive in the case of weak rain. Less