Read the passage and answer the question. A landslide is defined as the movement of a mass of rock, debris or earth down a slope. Landslides are a type of 'mass wasting', which denotes any down-slope movement of soil and rock under the direct influence of gravity. The term 'landslide' encompasses five modes of slope movement: falls, topples, slides, spreads and flows. These are further subdivided by the type of geologic material (bedrock, debris or earth). Debris flows, commonly referred to as mudflows or mudslides, and rock falls are examples of common landslide types. Almost every landslide has multiple causes. Slope movement occurs when forces acting down-slope, mainly due to gravity, exceed the strength of the earth materials that compose the slope. Causes include factors that increase the effects of down-slope forces and factors that contribute to low or reduced strength. Landslides can be initiated in slopes already on the verge of movement by rainfall, snowmelt, changes in water level, etc. Which is the most suitable title for the passage?

1. Earthquakes and Their Impacts
2. The Growth of Mountain Ranges
3. River Systems and Floodplains
4. Causes and Types of Landslides