It is similar to the Brule in that volcanic ash still makes up a significant portion of the sediment, but the Gering typically contains more concretions. Concretions are rounded features that have been cemented more completely than the surrounding sediment. They may be formed by cementation around a nucleus of organic material or by groundwater circulating through the rocks. 18.6 Slumping hills. A slump is a form of mass wasting , or downslope movement.
Slumps occur where unconsolidated sediments move downhill on a curved, scoop-shaped surface.
The scar left at the top of the slump block is called a scarp . The scarp for this slump is covered with grass, indicating that it has not moved in some time. The landscape here has been carved by gullies, which have cut through the layer of protective sod and exposed softer sedimentary rocks underneath. 20.0 Hillside with more erosion and slumping. The road log now enters the area known as the Nebraska Sand Hills.