Soil erosion is mainly due to which of the following reasons?

wave action

earthquakes

heavy rainfall

deforestation

D. Deforestation. When we have forests, they provide roots witch hold dirt in place.

No trees = no firm foundation

The correct answer is - deforestation.

Deforestation is a huge issue when it comes to soil erosion. When there's thicker vegetation the soil is in place and the erosion is minimal. This is due to the root systems of the trees, bushes, grashes, that are making a natural net inside the soil that holds it in place and doesn't allow the soil to be moved away and thus erosion to take place. But when we have a deforested landscape than the situation is the total opposite. The soil is left on its own and it doesn't have any protection from the root systems to keep in place, so with every rain it is eroding slowly and occasionally quickly when there's heavy rainfall. Most of the erosion takes place on the steeper parts.