Weathering, mass movement & slope stability

Stand on any hillside and ask a simple question: why does the material on a slope sometimes stay put, and sometimes come creeping, flowing, sliding or crashing downhill? In this AS lesson we first pin down the crucial difference between weathering (the breakdown of rock in place) and mass movement (the downslope movement of material under gravity). We then classify every kind of movement by its speed and its water content — from imperceptibly slow soil creep and solifluction, through earth flows and mudflows, to rapid slides and very rapid rock fall — and see them all on one labelled slope. We examine the effects on people and the natural environment, work through a case study of how human activity (deforestation, cutting and overloading) destabilises slopes, and finally evaluate the four main strategies used to hold slopes in place: pinning, netting, grading and afforestation.