Soil erosion is an ongoing problem for gardeners. Heavy rainfall, steep grades, and other environmental factors all contribute to erosion. Good landscape design and limiting traffic by humans and animals can help to prevent soil erosion and minimize its effects.
Mass movement is the movement of rocks and soil particles downhill due to gravity. Soil creep is one of the slowest and least dramatic forms a mass movement. Individual soil particles roll downhill through time, gradually eroding the terrain.
A rapid mass movement example is the rock avalanche, where huge rock structures collapse and roll downhill in a dramatic cascade.
Humans and animals walking on a landscape will also contribute to mass movement by knocking soil particles and rocks lose.
Land slips are a form of mass movement caused by excessive rainfall. Soils with a lot of clay absorb and retain water, becoming heavier. The water also lubricates clay, allowing it to break loose and slide downhill.
Water erosion occurs when water detaches dirt particles and transports them to another location. In a rainstorm, the first stage of water erosion is splash erosion. Individual drops of water strike the ground, creating miniature craters and catapulting soil particles off along with smaller droplets of water. The raindrops also slightly compact the soil, creating a thin crust that allows water to flow along the surface rather than being absorbed.
As the rain continues, the water flowing over the surface can form into a sheet, a process called sheet erosion, which removes a whole layer of soil. More commonly, it forms channels called rills in the soil. The soil from the edges of these rills erodes, collapses, and is carried away, widening the rill and forming a gully. Through time, this form of erosion can carry away a lot of soil and destabilize the soil structure.
Wind erosion most commonly occurs on soil that is loose, dry, and not anchored by plants. The wind picks up particles, moving them and gradually eroding the soil. Large particles of soil may be rolled downhill, contributing to soil creep. Smaller particles, such as clay, are actually suspended in the wind and blown away. In areas with high winds and vulnerable soils, this process can remove significant amounts of topsoil, causing long-term damage to the soil.