Geological Survey Program
Landslides and rockfalls are potential hazards in areas that have steep topography. Most Missouri bluffs are fairly stable, but some can pose problems. The most hazardous are bluffs that contain thick beds of sandstone or carbonate rock, underlain by shale. The shale will often preferentially weather out to form a re-entrant beneath the harder rock, leaving large pieces of cantilevered rock. Rocks that fall from bluffs typically collect at their base. Geologists examine the bases of bluffs to estimate what size rockfalls they can produce.
Steep slopes of loess, till, thick colluvium, alluvium and shale can be prone to landsliding. The problem is often exacerbated by seasonally high water tables. In general, the higher and steeper the slope, the further and faster the slide will move. Look for scallop-shaped scars along the slope and uneven or undulating ground at the base of slopes. Modifying slope toes can cause problems, even on slopes that appear stable. Care should be taken when modifying slopes and changing natural water courses in unconsolidated materials. For more information about rockfalls or landslides contact the Geologic Resources Section at 573-368-2143 or email.