Aeolian Dune Deposits
Bermuda's Pleistocene dunes were coastal. Their source of sand was the beach, which in turn, depended on a source from the sea. Where there was no beach, with an ample supply of sand, there was no opportunity for dune growth.
Coastal dune activity, associated with beaches, was intermittent in Bermuda. When the dunes were temporarily inactive, due to an inadequate supply of sand or lack of sufficiently strong onshore winds, rainfall and the establishment of vegetation caused cementation and stabilization of the sand. These processes, combined with the barriers such as hills and tree-lines, were responsible for restricting dune migration.
The relative immobility of Bermuda's dunes is demonstrated
by the arrangement of dunes into ridgelines that parallel the coast. Each
ridgeline is composed of coastal dunes which were unable to break-free
and migrate from their associated source-beaches. Some exceptions to the
"beach-tied" pattern of dune deposition are recorded in Bermuda's
geology. Obviously, one or more of the conditions which usually limited
dune migration were not in effect when these dunes were built.