What is the movement characterized as a rotational type with few units involved?

The movement characterized as a rotational type with few units involved is typically identified as a slump. A slump occurs when a mass of material moves down a slope along a curved surface, which distinguishes it from other types of mass wasting. This rotational movement generally results in a distinct scarp (or cliff-like feature) at the head of the slump and a bulging toe at the base where the material accumulates.

In a slump, the movement is often limited to a relatively small area, making it different from other types of landslide or mass movements that may involve larger masses of material. The curved surface along which slumping occurs contributes to the rotational aspect of the movement, contrasting with translational movements like slides, where the material moves along a planar surface. Understanding this mechanism is essential for assessing slope stability and the potential for erosion or landform changes in geological studies.