Answer:
Many Reasons can be the cause for cracks in sidewalks. Tree roots might be underneath the sidewalk and when they are not strong enough to lift the whole slab, it slowly uses its forth to slowly break the concrete causing cracks. The next reason is the same for both potholes and sidewalks. The expansion and contraction of water that has entered the ground underneath the pavement will eventually freeze, and what does freezing water do? it expands so when it keeps getting thawed and froze, the pavement weakens and eventually leads to cracks and potholes.