English: About 6,000 years ago, before extensive wave erosion of the glacial deposits had occurred, glacial Cape Cod probably resembled the green area as shown on the left map. At first, headlands composed of glacial drift, east of the present eastern shore of the Cape, began to erode as waves attacked the fragile land to form marine scarps or sea cliffs.

The sea, however, does not simply destroy the land. Much of the eroded material is reworked and transported along the shore by longshore drift and longshore currents generated by the oblique approach of the waves. This transported material is redeposited along the shore to form new land. The sand is transported and redeposited to form bay mouth bars, spits, and barrier islands across embayments in the coastline.

The present pattern of erosion is shown on the map on the right. Red shows shoreline undergoing wave erosion; green shows shoreline undergoing deposition. However, in many places, the shoreline of the depositional features is migrating landward.