Conditions favoring mass wasting can exist in an area for a long time without movement occurring. An additional factor is sometimes necessary to trigger the movement. Among the more important and dramatic triggers are earthquakes. An earthquake and its aftershocks can dislodge enormous volumes of rock and unconsolidated material. The mass-wasting event shown in Figure 4.29 was triggered by an earthquake. In many areas that are jolted by earthquakes, it is not ground vibrations directly