These can be a single line of works along the crest of a hill, or a rifle pit used by a single soldier. The primary threat to earthworks is erosion. Erosion is the movement of soil from one location to another, by water, wind, or gravity. This can be detrimental to earthworks in two ways. Besides reducing the size of and destroying the form of parapet walls, erosion can also fill in and obscure trenches.
Most erosion is caused when the vegetation which serves to hold soil in place is damaged or removed.
This can be caused by both natural phenomena and human impacts. These impacts can effect earthworks existing under different conditions in different ways. Most earthworks today can be categorized as being under one of two basic types of vegetative cover. These are forest cover and grass or herbaceous cover. The effects of erosion as well as the prevalence of the various impacts leading to it can vary greatly, depending on the condition and type of existing vegetation.