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It is a very urgent subject for our country to survey physical process of rocky mudflow which has been causing serious damages in mountainous regions every year.There seems to be various methods to approach the essential phenomena of rocky mudflow, and field survey after the occurrence of mudflow or experimental study of mudflow has been comparatively well undergone as an effective method. But a direct observation has been hardly planned on moving process of actual mudflow because of the danger of observer and difficulty of recording.Considering above situation, in order to carry out a systematic and exact observation on moving state of rocky mudflow, a new synthetic observation system has been developed by Mudflow Research Group.This observation system consists of velocity sensors connected with time recorder for the measurement of local variation of front velocity and 8 mm cine cameras, 16 mm cine camera, videocamera, a pair of stereo cameras to analyze the dynamic movement of mudflow front, and strain gauge to record the impact force of mudflow. All these instruments are ready for automatic recording.In addition to above system, rain gauges and mud samplers were set in the same observation area to study occurrence condition and physical property of flowing substance.After the preliminary test in 1970, a field test of whole system was carried out in 1971 at Valley Kamihori on eastern slope of Mt. Yake, North Japan Alps, Nagano Prefecture.In the morning on 6 th Sept. 1971, our new system succeeded in recording the motion of rocky mudflow several times, and valuable information about it was got from this record in relation to hydrological and microtopographical conditions.A general explanation on the observation in 1971 are described in this paper, accompanied with some reviews of present state of mudflow research.

It is a very important subject for our country to survey physical processes of rocky mudflow causing serious damages in mountaineous regions. In order to carry out an systematic and exact observation on moving state of rocky mudflow, a new synthetic observation system was developed by Mudflow Research Group.The system consists of velocity sensors connected with time recorder for the measurement of local variation of front velocity and 8 mm cine cameras, 16 mm cine camera, 35 mm constant interval shot camera, video camera and stereo cameras, which are ready for automatic recording of moving pattern and form of mudflow.In addition to the system, rain gauges and mud samplers were set in the same observation area to study water balance and physical property of flowing substance.After a preliminary test in 1970, a field test of the whole system was carried on in 1971 at Valley Kamihori on eastern slope of Mt. Yake, North Japan Alps.In the morning on 6 th, Sept. 1971, our new system succeeded in recording the motion of rocky mudflow several times, and valuable information about mudflow was got in relation to hydrological and microtopographical conditions.A general explanation on the observation system and a part of the results obtained from field test in 1971 are described in this paper.