Dunes and coastal banks are sometimes confused with one another. Although coastal banks are subject to erosion, they remain relatively stable over time. Dunes are deposited by and move with wind and wave action. Dunes are composed of materials deposited recently (since the last glacier). Coastal banks are generally (not always) composed of materials that predate the last glacial period.

The State Act defines a dune as a "natural hill, mound or ridge of sediment landward of a coastal beach deposited by wind action or storm overwash." A definition of dune can be found in the State regulations at CMR 10.28 (2).

In addition:
  • Dunes may or may not be vegetated.
  • Some coastal areas may have several sets of dunes extending landward.
  • Some dunes may contain sediment that has been artificially deposited for the purpose of storm damage prevention.