The role of seepage moisture in soil formation, slope development, and stream initiation

Abstract

Field study of the podsolized soils and the drainge of an escarpment of Chatsworth gritstone *upper Namurian) in Northern England has suggested hypotheses relatige to stream initiation and crestal development. Moisture moving from crests over dip slopes of less than five degrees becomes concentrated in narrow lines of relatively deep soil of distincive phase. These lines are sermed "seepage lines" and form a densdritic pattern linked directly to visible drainage lines. Colluvium has gathered in certain depressions at the head of visible scarp and dip streams, and corrosion of the underlying bedrock, by accumulated seepage moisutre, is taking place at depth. This corrosion of bedrock in seepage hollows is considerd to be a major factor in the headward extension of first-order streams. Moisture accumulation on creastal areas is limited so that corrosion and soil formation take place but slowly, or not at all, with rock bastions or "tors" located upon it, the heights of which represent the thickness of material removed from the adjacent slopes by a combination of periglacial mass-wasting and post-glacial surface and subsurface denudation. Detailed studies of the soil mantle on such low-angle slopes on a uniform bedrock material have failed to establish any simple relationship of soil depth, profile, or texture with degree of slope or fact type. Position on the total slope in relation to the seepage net and indirectly to the drainage net is the most signficant factor in soil formation and hence in slope development and denudation.