Downslope movements of rock and soil, collectively called landslides, cause many millions of dollar of damage yearly in Ohio. These gravity driven movements occur in many areas of the state where slopes and failure-prone materials exist. Although such movements occur naturally, many landslides are triggered by human activities.
Slow, downslope movements of unconsolidated surface materials called creep, is widespread as can be noted by tilting fence posts, cemetery monuments, telephone poles, and other objects that through time have slowly moved from their original vertical position. Creep is partly a result of alternate freeze-thaw cycles pushing grains apart.
Rotational slumps involve large blocks of rock or sediment that move as a unit along a glide plane. The bottom portion, or toe, of the slump moves outward and downward whereas the top portion of the slump block moves downward but tilts backward. Trees on top of the tilted block lean upslope. Rotational slumps commonly occur in red-colored shales of Pennsylvanian age in southeastern Ohio.
Earthflows occur in unconsolidated materials that are saturated with water and lose the bearing strength of grain-to-grain contact. The sediment moves down slope in a series of lobate flows.
All of these movements are relatively slow and, although seriously damaging to property and structures, generally do not pose an immediate threat to human life. However, rockfall is a category that can be of considerable danger because it involves a large amount of rock that suddenly moves downslope with little or no warning. Generally, rockfalls occur in thick, massive sandstones that are cut by vertical joints. Undercutting of the less-resistant rock beneath the sandstone, either by natural processes or human activities, removes support for the overlying sandstone. Water that penetrates a vertical joint tends to pry the block loose from the outcrop by freezing. Ohio