Final answer:
Subsidence is the downward motion of land due to causes like soil compaction, mineral extraction, and water withdrawal. It can be exacerbated by natural events such as erosion, earthquakes, and heavy rainfall, as well as human activities like irrigation. Over time, soil develops and changes, which can also contribute to the process of subsidence.
Step-by-step explanation:
Gradual subsidence is the downward motion of land that can be attributed to various natural and anthropogenic causes. It often occurs due to soil compaction, extraction of mineral resources such as natural gas, and withdrawal of ground and water. With erosion by rivers, glaciers, and ocean waves, over-steepened slopes can become weak and susceptible to failure. Heavy rains, snowmelt, and geological events such as earthquakes and volcanic eruptions can increase the stress on these slopes, potentially leading to subsidence. Furthermore, human activities like irrigation, which leads to the saturation of soil, and the construction of heavy structures can exacerbate the process. When it comes to the development of soil profiles, soils change over time, and this can also contribute to subsidence. Gradual geological processes cause soils to become thicker and more developed, but this rate of change decreases over time, eventually reaching an equilibrium.
Sinkholes and other forms of subsidence are also related to the dissolution of limestone by acidic solutions in groundwater, which can create large cavities that collapse over time. The process of solifluction, often mistaken for terraces created by sheep, illustrates a small-scale type of subsidence where soil creeps downhill during freeze-thaw cycles, leading to the gradual formation of terraces.
Understanding subsidence is crucial for managing risks associated with construction and urban development, as well as for preserving natural landscapes vulnerable to this phenomenon.