The correct option is 1, 2, 3 and 4.
Explanation
Mass movements (or mass wasting) refer to the transfer of rock debris or soil down a slope under the direct influence of gravity. While gravity is the primary driving force, various conditioning factors such as lithology, stratigraphy, vegetation, and climate significantly influence the activation of these movements.
Statement-wise Analysis
- Statement 1 is Correct: Weak, unconsolidated materials (such as loose soil, clay, or fractured rock) possess low shear strength and cohesion. These materials are inherently unstable and are easily displaced by gravity, facilitating mass movements like slumps or earthflows.
- Statement 2 is Correct: Steeply dipping beds, especially those dipping parallel to the slope surface, provide a plane of weakness. This structural alignment reduces friction and allows rock layers or debris to slide downwards more easily compared to horizontal or inward-dipping beds.
- Statement 3 is Correct: Vegetation plays a crucial role in slope stability as roots bind soil particles together and regulate water content. The scarcity or removal of vegetation eliminates this binding effect, making the soil loose and highly susceptible to erosion and mass wasting.
- Statement 4 is Correct: Abundant precipitation acts as a trigger for mass movements in two ways: it adds weight to the slope material (overburden), and it increases pore water pressure, which reduces the frictional resistance (shear strength) between particles, causing the material to slide or flow.
Key Takeaway
Key Takeaway: Mass movements are driven by gravity but are favored by factors that reduce the shear strength of materials (water, weak lithology) or increase shear stress (steep slopes, removal of support).