SLOPE HEIGHT Cohesion allows slopes to stand at angles φ (angle of internal friction of the rock or soil). Frictional resistance, effective stress and driving force are all functions of mass, increasing with slope height; cohesion is a function of area, independent of height, so it has less proportional effect in high slopes. Low slopes can therefore stand at steeper angles than high slopes in same material. Intact rock (horizontally bedded) will stand in vertical cliffs of height limited only by UCS; coastal cliffs in weak chalk stand 150 m high. Height and slope of natural and cut faces is limited by fractures – mainly their orientation, also density, roughness and shear resistance. High slopes in dry materials all have stable angles that approach the lesser of φ or the dip of significant structural weaknesses that daylight in the slope.