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Tales of the Coast
America's Coasts

Glaciated Coast

During the Pleistocene epoch, massive continental glaciers, similar to the present Greenland and Antarctic ice caps, covered broad parts of the continents. The glaciers waxed and waned in cycles, probably because of climatic variations, causing vast changes to the morphology of coastal regions in the northern latitudes. As a result, glacially modified features dominate the northern coasts and continental shelves, although in many areas marine processes have reworked the shore and substantially modified the glacial imprint.

The most spectacular erosion forms are drowned glacial valleys known as fjords. The over-deepened valleys were invaded by the sea as sea level rose during the Holocene epoch. Today, fjords retain the typical U-shaped profile that is also seen in formerly glaciated mountain valleys. Fjords and other drowned glacial erosion features give Maine a spectacular, rugged coastline.

A fundamental division of coastal characteristics occurs along the Atlantic coast of North America due to the presence of glacial moraines. The Wisconsin terminal moraine formed a prominent series of islands (i.e., Long Island, Block Island, Nantucket, and Martha's Vineyard) and offshore banks (Georges and Nova Scotian Banks). South of the moraine, the topography is flatter and more regular, except for piedmont streams, which intersect the coastal plain.

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Glaciated coast
Source: National Oceanic & Atmospheric Adminstration (NOAA)

Glaciated Coasts

Coasts altered by glaciers usually have offshore regions that are highly dissected by relict drainage systems. These sinuous stream channels display highly irregular and varied topography. They are composed of sediment types ranging from outwash sand and gravels, to till, which consists of many types of intermingled sediments from clay to boulders.

Pleistocene Period: The geological period from about 1.8 million years ago to 8,000 years ago.

Holocene Period: The most recent geological period from about 8,000 years ago to the present.