Studies on Depositional Structure and Formative Process of Soil and Weathering Debris in Mountain Slope

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We have assumed following problem of pedological and topographical phenomena. and obtained corroboration concerning about formative process of soil and topography.Soil and topography were deformed accidentary by volcanic action. mainly pyroclastic flow and volcanic ash in 7.5x <10^4> years and 2.2x <10^4> years ago.・ Large zone of Kyushu disrict was coated with high temperature deposits of large-scale pyroclastic flows (about diminished 200-300 <km^2> individually), and simultaneously most of forest were destroied and plant were lost, caused by high temperature.・ Infiltration capacity was extreamly decreased caused by the loss of plant.・ Gully erosion was acceleted violently with surface flow caused by the decrease in infiltration capacity.・ Channels with gully erosion were dissected in the slope and bearing point of slope body took away caused by stream flow in channels.・ Large-scale and great many landslides occured in moutain slope caused by loss of bearing point. ・ All of soil was carried away and all of slope was bared.After the accident. forest would be recovered quitely and it would accompanied with increase of infiltration capacity and decrease of landslides. gully erosion as following process.・ Soil was formated with depositional agent of plant registance.・ Infiltration capacity increse. -> Surface flow decrease. -> Gully erosion decrease. -> Land slides decrease.Physical weathering supplied with debris from bed rock, and volcanic eruptions supplied with fine soil from ash Recent erosion : Soil erosion caused by accidental heavy rain. Recent landslide : Destruction of soil structure caused by subsurface flow and groud water.