Usually this means erosion somewhere else. Text Box Figure 11.1 Sea level may be rising as a result of melting of icecaps caused by global warming. On the other hand, it could be going up as part of a long-term cycle we don't understand very well. Local sea level changes occur as well, so it is difficult to gage, but satellite altimetry definitly shows an increase. Estuaries are defined as bays where freshwater mixes with seawater.
Estuaries form where rivers widen at the coast.
Because freshwater is less dense than saltwater, the interaction between the two usually involves some stratification , whereby the fresher water overlies salt water. This tendency can be counteracted by turbulence due to tidal currents, which can be strong enough to break down stratification. Stratification is strongest in deep estuaries with weak tidal flow. River flow enters the fjord and flows outward at the surface, entraining some salt water as it goes. This means that surface salinity increases going seaward, and also that flow near the bottom must be into the estuary.