Erosion refers to processes in which external elements (wind, water, etc.) remove soil or rock from a certain location and transport it to another location. There are a variety of different erosion types, including river and gull erosion, wind erosion, and erosion attributed to human activity. Erosion ultimately destabilizes soil and can lead to landslides and sinkholes.
One of the most common causes of unstable soil is poor compaction. In some cases, certain types of soil are simply very loose and subsequently not compact. The cause of this is typically an imbalance of mineral pieces, organic matter, air, and water. For example, a clay soil with very high moisture content will inevitably become instable, as it will be incredibly difficult to compact. Similarly, soils with high sand content will be difficult to compact.
Processes of freezing and thawing essentially accelerate erosion processes. Cold weather freezes moisture trapped in tiny cracks. When this water freezes, it expands, subsequently pushing on the rocks and breaking them into smaller pieces. As processes of freezing and thawing continue, rock and sediment are continually broken down.
When soils contain a high concentration of organic materials, such as topsoil and plant matter, it will decompose, subsequently causing it to become unstable. This is because organic materials rapidly change form and mass as they decompose in soil. In fact, up to 90 percent of organic material will disappear over the course of the decomposition process.