Which landslide type features rotational backward movement of the displaced material?

The correct answer is Slump.

Understanding Landslide Types and Their Movements:

Mass wasting operations (or landslides) are classified based on the material involved (rock, soil, debris) and the type of movement (fall, slide, flow, or slump).

1. Slump:
A slump occurs when a coherent mass of rock or unconsolidated soil moves downward and backward along a curved, concave-upward rupture surface (slip plane). As the mass moves down the curve, the upper surface of the block tilts backward toward the slope. This distinct backward rotational movement along a curved surface is the defining feature of a slump.

2. Rockslide:
A rockslide involves the rapid sliding of bedrock along a planar or flat surface (such as bedding planes or joint surfaces) rather than a curved surface. The movement is transitional, not rotational.

3. Rock fall / Debris fall:
Falls involve the free-fall of detached individual rocks or loose debris through the air from steep cliffs or slopes. They do not slide along a surface.

Therefore, the landslide type characterized by rotational backward movement of displaced material is a Slump.