Final answer:
Subsidence is the compaction of sub-surface sediments due to water loss, leading to land sinking. It's caused by various factors, including resource extraction and groundwater withdrawal. Retrogradation is related, but specifically refers to shoreline retreat due to sediment and subsidence imbalance.
Step-by-step explanation:
The correct definition of subsidence is the compaction of underlying sediments due to the loss of water in pore spaces. Subsidence refers to the downward motion of land, which can happen for various reasons, including soil compaction, extraction of natural resources like gas, and the withdrawal of ground and water. This can lead to issues such as sinkholes, reduced aquifer capacity, and damage to human structures.
Retrogradation is a related process where the shoreline moves landward because the rate of subsidence outpaces sedimentation. The water table typically reflects the topography of the surface and fluctuates with weather conditions, affected by various factors including rainfall and evapotranspiration. During times of drought, the water table may lower, and during periods of heavy rainfall, it may rise. Persistent drainage of water from the ground, like through heavy agricultural irrigation or groundwater mining, can exacerbate subsidence.