The correct option is (a).
Explanation
Landslides are a form of mass wasting, defined as the movement of a mass of rock, debris, or earth down a slope under the direct influence of gravity. They are geological hazards influenced by slope stability, lithology, and external triggers.
Statement-wise Analysis:
- Statement 1 is Correct: A landslide is scientifically defined as the movement of a mass of rock, debris, or earth down a slope. This term encompasses five modes of slope movement: falls, topples, slides, spreads, and flows.
- Statement 2 is Incorrect: Landslides can occur in conjunction with earthquakes and volcanic eruptions. However, they are also frequently associated with floods. Heavy rainfall and flooding saturate soil and rock, increasing pore water pressure and reducing the shear strength of the slope material, which triggers mass movement.
- Statement 3 is Incorrect: Intense blasting, often used in mining, quarrying, and infrastructure development, generates ground vibrations and fractures rock formations. This significantly reduces the stability of slopes and acts as a major anthropogenic trigger for landslides.
Key Takeaway:
Landslides are triggered by a combination of natural factors (earthquakes, volcanoes, heavy rainfall/floods) and anthropogenic factors (blasting, deforestation, unscientific construction).