Which change would cause the topsoil an area to increase in thickness?

An increase in vegetation, such as the growth of deeper-rooted plants and trees, can contribute to the thickening of topsoil. These plants enhance soil structure and organic matter through root decay and the accumulation of leaf litter, which enriches the soil. Additionally, reduced erosion due to better ground cover and practices like no-till farming can help retain topsoil, allowing it to build up over time. Lastly, improved soil management practices, like crop rotation and cover cropping, can also lead to thicker topsoil.