Answer: In some cases the soil settles unevenly over time, perhaps because of fill used beneath the top soil or due to excavation at some earlier time. The settling process takes many years and regrading is an expensive solution. In other cases there are moles or other animals at work tunneling and this can cause surface changes. Finally, the ground may heave somewhat naturally during fall and spring freeze and thaw cycles. This is what the old fashioned lawn roller was used to correct, although it also compacts the soil and makes ir tough for the grass roots to penentrate. If the lawn is healthy you may not need to do anything, but you might want to consult with your county extension and see if you can determine the cause of the changes and what steps you can take.
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