Salt Marsh - Cape Cod National Seashore - Eastham, MA - Places of Geologic Significance on Waymarking.com

A bird’s eye view of Cape Cod reveals a landscape dimpled with holes. Most of them are nearly round, and many are filled with water, like Salt Pond in front of you.

Geologist call these intriguing depression’s “kettles.” They were formed over 18,000 years ago when the gigantic ice-age glaciers that covert this region began to melt.

Salt pond is unique among the kettles of the outer Cape because it has been captured by the ocean. The title channel from Nauset March has breached the opposite side of the kettle, allowing salt water to enter. Water levels rise and fall twice daily with the tides.

[Caption lower left]
The huge ice block that helped to create Salt Pond probably covered an area larger than four football fields.

[Caption center]
Kettles begin to form when blocks of ice become surrounded or buried by layers of clay, sand, and gravel that are deposited by streams at the edge of a melting ice sheet.

The depressions that remain after the ice block melts called “kettles.” Kettles which fall below the local water table fill with water to become “kattle ponds.”

[Caption right]
“Some of the valleys… are circular, a hundred feet deep without any outlet, as if the Cape had sunk in these places, or its sand his run out. “

Cape Cod
Henry David Thoreau
1865

Some kettles eventually filled with dead vegetable matter, creating a bog. Several such bogs on the Cape are used for cranberry growing.