Why do fjords have sills?

Question

I have read about some of the geologic processes that are related to the formation of fjords. Is the presence of sills in fjords related to the deposition of glacial moraine?

Answer 1

The sills you are asking about are a product of the "overdeepening" process. Glacial erosion is most efficient at the base of the ice, increasing channel incision occurs when topographic features restrict the flow into a narrow valley. The erosional power is diminished at the terminal moraine, preserving the sill and allowing for deposition of debris.

NOTE: This glacial overdeepening is distinct from river overdeepening. And these fjord sills are distinct from sills created by igneous intrusions.