Nantucket Barrier Beach and Wildlife Refuge Becomes a National Natural Landmark

The National Park Service has announced that Nantucket Barrier Beach and Wildlife Refuge in Nantucket County, Massachusetts, has been named a National Natural Landmark (NNL) by Secretary of the Interior Deb Haaland, bringing the number of NNLs in the United States to 606.

What makes it special

The site, about 1,600 acres on the northern extension of Nantucket Island, 30 miles south of Cape Cod, showcases two landforms: a world-class example of a rhythmic cuspate spit series and a large, well-developed, symmetrical cuspate foreland. It is also home to many plants and animals.

Barrier beach terms

• A barrier beach is land built by waves, wind and tides moving sand, separating a smaller body of water (such as a pond) from a larger one (such as the ocean).
• A barrier spit is a long, narrow barrier beach extending into the water from the mainland.
• A cuspate foreland is a curved stretch of beach facing a large body of water, where wind and waves travel unlimited distances.
• Cuspate spits are curved projections of beach into an enclosed or partly enclosed body of water, where the distance wind and waves can travel is limited.

How the beaches formed

The barrier beach complex formed over thousands of years, beginning with glacial deposits some 23,000 to 24,000 years ago. As the ice melted and sea levels rose at the end of the last ice age, islands like Nantucket appeared off the East Coast as glacial deposits were cut off from the mainland.

Wind and waves then carried sand north and northwest along Nantucket's north side, first connecting the island to the triangular, 0.6-mile-wide Coskata Island, then building another 3.2-mile barrier spit out to Great Point. A few thousand years ago, as sea level rise slowed, sand moving south from Great Point began forming Coatue, a 6.5-mile barrier spit that separates Nantucket Harbor from Nantucket Sound.

Coatue's two shores face very different waters, and they look it. Its northwestern shore, open to the unlimited wind and waves of Nantucket Sound, is a long, sweeping cuspate foreland. Its southeastern shore, inside the harbor, has six curved sandy points jutting into the water; seen from above, the scalloped beach between them looks like the edge of a bread knife.

Three processes created and maintain those cuspate spits: an ample sand supply along a stable coast; the harbor's long axis lining up with the seasonal winds and waves; and a "Goldilocks" tidal range, low enough for barrier beaches to form but high enough to erode the spit tips. The spits form a self-organized system in balance, so losing or disrupting any of the surrounding barrier beach features or processes would change or destroy this rare coastal feature.

National significance

The series of symmetrical cuspate spits is easily the best organized and formed on the Atlantic Coastal Plain, and it remains nearly pristine: largely free of engineering and development, its shoreline erodes and builds up naturally. Cuspate spit series are rare worldwide. Coatue's cuspate foreland, nearly 6.5 miles long, is the largest in the Outer Lands portion of the Atlantic Coastal Plain, remarkable for its symmetry and continuity.

A home for wildlife

A piping plover at Nantucket National Wildlife Refuge. Amanda Boyd/USFWS.

The varied coastal features also provide vital habitat. Glacial outwash supports old-growth oak forest, shoreline and beach deposits support eastern red cedar forest, ancient dune ridges carry shrubs and tidal salt marshes, and even the spits jutting into the harbor hold saltwater tidal and brackish marshes. These plant communities and dune and beach complexes support rare plants and offer rich, unbroken habitat for wildlife, including vital nesting sites for the piping plover, a federally threatened bird.

Seals at Nantucket National Wildlife Refuge. Amanda Boyd/USFWS.

Caretakers

The entire landmark is owned and managed by The Trustees of Reservations, the Nantucket Conservation Foundation and the U.S. Fish and Wildlife Service, which work together to protect it. The site is an outdoor laboratory for studying coastal processes found in few other places and a chance to teach how barrier beaches form and work. Designation recognizes its outstanding features and encourages its conservation, alongside hundreds of other landmarks representing the nation's biological and geological heritage.

Sources

• National Park Service, "Nantucket Barrier Beach and Wildlife Refuge: A New National Natural Landmark." https://www.nps.gov/articles/000/nantucket-barrier-beach-and-wildlife-refuge-a-new-national-natural-landmark.htm
• The site was evaluated by Dr. Nicholas L. Venti and peer-reviewed by Drs. Christopher Hein, Robert Cook, Zoe Hughes and Stephanie Stotts. More: The Trustees, Coskata-Coatue Wildlife Refuge: https://thetrustees.org/place/coskata-coatue-wildlife-refuge/; Nantucket Conservation Foundation, Coatue: https://www.nantucketconservation.org/properties/coatue/; USFWS, Nantucket National Wildlife Refuge: https://www.fws.gov/refuge/nantucket
• A Google Earth image and a photograph by the evaluating geologist are not reproduced here.