Fjords (pronounced fee-YORDS) are typically long, narrow valleys with steep sides that were created by advancing glaciers. As the glaciers receded they left deep channels carved into the earth with a shallow barrier, or narrow sill, near the ocean. The sill restricts water circulation with the open ocean and dense seawater seldom flows up over the sill into the estuary. Typically, only the less dense fresh water near the surface flows over the sill and out toward the ocean. These factors cause fjords to experience very little tidal mixing; thus, the water remains highly stratified. Fjords are found along glaciated coastlines such as those of British Columbia, Alaska, Chile, New Zealand, and Norway.
In the animation below, the blue-colored fresh water is seen flowing over the narrow sill of the fjord on the far right-hand side of the image into the ocean. Almost none of the green-colored seawater is able to make it over the sill into the estuary.