Final answer:
The rates of coastal recession vary because of eustatic changes in sea level, local topography and bathymetry affecting tidal ranges, and human-induced climate change factors.
These cause variation in the erosion and deposition processes at coastlines.
Step-by-step explanation:
The rates of coastal recession vary over time due to a variety of factors. These factors include eustatic changes, which are worldwide changes in sea level due to changes in the volume of water in the oceans or ice sheets.
For example, during periods of sea-level rise, known as transgression, the sediment package deposited along coastlines is stacked on top of each other towards the shoreline in a pattern known as onlapping.
Conversely, during a sea-level fall or regression, the sediment package moves away from the coastline in an offlapping pattern, contributing to coastal regression.
The rates of coastal erosion and recession can also be influenced by the local topography and bathymetry of the shoreline, which affect the range of tides. High tidal ranges, such as those at the Bay of Fundy, can result in more significant coastal impacts.
Additionally, tides, the alternate rising and falling of sea level, play a role in the erosion process. Human-induced factors like CO₂ emissions also contribute to the warming of oceans and melting of ice, which indirectly contribute to shifts in coastal lines over time due to sea-level changes.
Understanding coastal erosion processes is critical in preparing for and mitigating the impacts of sea-level changes on human structures and ecosystems.
With the ongoing climate change, the rates at which coastlines erode are becoming increasingly important for coastal management and planning.