Correct Option
The correct option is Debris slide.
Explanation
Mass movements involve the detachment and downslope transport of soil and rock material under the influence of gravity. These movements are classified based on the mechanism of movement (fall, slide, flow) and the type of material involved (rock, debris, earth).
Option Analysis
- Slump Slump: Incorrect. A slump is a type of mass movement where one or several units of rock debris slip with a backward rotation with respect to the slope. It typically occurs along a curved failure plane. Since the question specifies movement "without backward rotation," this option is invalid.
- Debris slide Debris slide: Correct. A debris slide is characterized by the rapid rolling or sliding of earth debris without backward rotation. In this process, the mass moves translationally along a relatively planar surface rather than rotating along a curved surface.
- Debris fall Debris fall: Incorrect. A debris fall involves the nearly free fall of earth debris from a vertical or overhanging face. The primary mechanism is falling through the air, not sliding along a surface.
- Rock fall Rock fall: Incorrect. Rock fall refers specifically to the free falling of rock blocks from a steep cliff or slope. It is distinct from a slide, which implies continuous contact with the slope surface during movement.
Key Takeaway: The critical distinction between a slump and a slide lies in the mechanics of movement: slumps involve rotational movement on a curved plane, whereas slides involve translational movement (sliding) on a planar surface without rotation.