The Geology of Cape Hatteras National Seashore: Young, Restless Barrier Islands

Geodiversity is the full variety of a park's natural geologic and soil resources and processes — rocks, minerals, sediments, fossils, landforms and the processes that shape them. The NPS Geodiversity Atlas, a product of the Geologic Resources Inventory, supports education, geoconservation, and management of a park's living and non-living parts together. This is its page for Cape Hatteras National Seashore, North Carolina.

The Geologic Resources Inventory report for the park.

The seashore

Cape Hatteras is part of North Carolina's Outer Banks, a barrier island chain in the Atlantic Coastal Plain. It was set up to keep the islands' wild and primitive character, protect their plants and animals, and offer compatible recreation.

• The islands are mostly long and narrow, separated from the mainland by wide, shallow sounds.
• Their habitats, shaped by natural coastal processes and by people, support native mammals, reptiles, amphibians, many marine invertebrates, and several federally threatened or endangered species, and are important for birds breeding, migrating and wintering.
• The estuary holds large marshes and underwater vegetation; inland forests protect the areas that recharge the freshwater aquifer.

How the islands formed

The Outer Banks are geologically young, built by the rise and fall of sea level:

1. About 5.3 million years ago, sea level was much higher, and marine sediments covered much of today's coastal plain.
2. From 2.6 million years ago, repeated ice ages raised and lowered the sea, and rivers cut valleys into those sediments — an old landscape that still controls the shape and depth of the estuaries and where the islands sit.
3. Over the last 10,000 years, as the sea rose to its present level, Holocene sediments filled and buried those old river channels.

So beneath the islands lies a mix of marine, coastal, estuarine and river deposits — from compact peat and mud to loose sand, gravel and shell beds. Modern storms, waves, tides, currents, inlets and sea-level change keep reworking them: much of the Outer Banks is under 3,000 years old, and some stretches under 500. People reshape them too, with dune building, dredging, stabilization and beach renourishment.

Coastal features and processes

Sunrise from Cape Point beach, Cape Hatteras National Seashore. NPS photo.

Fossils

• Quaternary marine shells are abundant on North Carolina beaches — up to 75% of beach shells in places.
• As the islands migrate landward, remains of forests and swamps that grew on their back sides are exposed — trees and peat hundreds to hundreds of thousands of years old.
• Old inlet deposits and the continental shelf supply more: algae, foraminifera, corals, bryozoans, mollusks, ostracodes, barnacles, echinoids and worm tubes.
• Vertebrates wash up too — including a walrus (Odobenus rosmarus) skull found on the beach at Salvo in 1990, radiocarbon-dated to 36,760 ± 570 years before present.

NPS fossils are protected by the Paleontological Resources Preservation Act of 2009.

Maps and reports

The seashore lies in the Coastal Plain province. Its Geologic Resources Inventory report covers these features and management issues in depth. More: the park's home page and the North Carolina Geological Survey.

The seashore's geomorphic map from the Geologic Resources Inventory.

Sources

Based on "NPS Geodiversity Atlas—Cape Hatteras National Seashore, North Carolina," National Park Service, drawing on Riggs et al. (1995), Stover (2002), Tweet et al. (2009) and others; a work of the United States government in the public domain.