15.2 What causes mass movements?
Fig 15.11
Under the conditions below, a brick on a board will slide if tilted far enough. What does this mean? 1) Increasing slope favors motion or slope instability. Next, we may sand the board and find it moves more easily. 2) Smoother surfaces favor motion and slope instability, and if we wet the board, it moves easier still; 3) the presence of
water favors motion and slope instability.
So slope angle, smoothness of surface, and presence of water all seem to enhance the tendency to slide down a slope.