How does a slowly rising sea level contribute to lagoon formation?

A slowly rising sea level plays a critical role in the formation of lagoons by flooding low-lying land situated behind a coastal barrier.1

When a barrier—such as a barrier island—is present, a gradual rise in sea level allows the area behind it to become inundated, creating a sheltered body of water. For this process to successfully form and maintain a lagoon, the barrier must be able to keep its elevation above the rising sea level. If the sea level rises too rapidly, the barrier may be drowned, causing the lagoon to cease to exist.12

Once formed, the lagoon persists until it is eventually filled with sediment. This relationship between rising water levels and coastal topography has been a significant factor in the development of many lagoons over the past 20,000 years.1