Chapter 13
Chapter 13: Unsafe Ground: Landslides and Other Mass Movements
Animation
This animation illustrates the process by which undercutting by waves removes the support beneath an overhang. Eventually the overhang breaks off along joints, a rock fall occurs, and the cliff retreats. For more information, see Section 13.3 Why Do Mass Movements Occur? starting on p. 368 and Figure 13.14 on p. 373 in your textbook.
In Earth’s gravity field, what goes up must come down—sometimes with disastrous consequences. Rock and regolith are not infinitely strong, so every now and then slopes or cliffs give way in response to gravity, and materials slide, tumble, or career downslope. This downslope movement, called mass movement, or mass wasting, is the first step in the process of erosion and sediment formation. For more information, see the Geology at a Glance: Mass Movement on pp. 370-371 in your textbook.