What process involves the increase in land area through natural deposits of soil?

Accretion refers to the gradual increase in land area that occurs when soil, sand, or other materials are naturally deposited over time by the movement of water, wind, or ice. This process can take place along riverbanks, shorelines, or deltas, where sediments carried by water settle and build up new land.

In contrast, erosion involves the removal and transportation of soil or rock, leading to a decrease in land area. Deposition describes the general act of material being laid down, but does not specifically imply an increase in land area as a result of natural processes. Landfill refers to a man-made process where waste materials are used to fill in areas, which differs from the natural process of accretion. Thus, the definition and implications of accretion make it the correct choice in the context of the question.