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N.C. Department of Environment and Natural Resources

NC Department of Environment and Natural Resources
Albemarle-Pamlico National Estuary Program - Geology

Albemarle-Pamlico National Estuary Program

 Geology of the Albemarle-Pamlico Estuarine System

The North Carolina coast didn't always look as it does today, and the Outer Banks have not always existed. Over millions of years, the sea has advanced and retreated. At the end of the earth's last ice age 18,000 years ago, the shoreline was located as much as 40 miles east of today's Outer Banks. During the warmest periods some 85 million years ago, the Albemarle-Pamlico shoreline retreated as far as today’s Interstate 95. Evidence of these changes can be seen today. You can follow sandy ridges of ancient coastlines—called scarps—throughout the Coastal Plain and find seashells imbedded in riverbanks far inland. By contrast, on some ocean beaches, the breaking waves churn up vintage tree stumps and layers of organic peat, the remnants of submerged woodlands.

Sea level was as much as 250 feet lower about 18,000 years ago. The area that is now Pamlico Sound was dry land covered with the type of plants found today only in much colder regions. Ancient rivers like the Neuse traveled in deep channels. As global climate warmed and chunks of polar ice melted back into the oceans, sea level began rising again. The rising Albemarle-Pamlico estuary drowned the forest, and the advancing ocean built up an unusually high sand ridge that has remained above sea level. That 160-mile-long ridge is the Outer Banks.

Most barrier islands moved landward during the last period of sea level rise, staying relatively close to the mainland. Though barrier islands are common along low-lying coastlines of the world, parts of the Outer Banks are unique in their long distance from the mainland. Spans of up to 40 miles separate the banks from the estuary's western edge. The enclosure formed by the banks makes the Pamlico Sound the largest embayed estuary in the world. The sound is nearly 100 miles from north to south and more than 25 miles wide in some places. Indeed, early European explorers searching for a shortcut to the Orient mistook the immense body of water for the Pacific Ocean.

Geologists do not agree on exactly when the banks were formed. It probably happened during the last period of rapid sea level rise between 3,500 and 5,000 years ago. Ocean levels have been comparatively stable since then. Barrier islands have survived additional rises in sea level (about 1 foot per century) by migrating landward—in effect, they roll over. Water washing over from the ocean carries and deposits new sediment to build up the land on the sound side. The Outer Banks have migrated as much as 50 miles inland since their formation.

Islands also move laterally—currents parallel to shore transport beach sand, causing some inlets to shift. Inlets shift continually, and areas of shoals and deltas constantly change location. Where Cape Hatteras elbows its way into the Atlantic, the shallow, treacherous Diamond Shoals stretch at least 15 miles seaward. Such shoals extending beyond the North Carolina capes created a navigational nightmare that had devastating consequences for early mariners. Skeletons of hundreds of sunken ships are still buried in this "graveyard of the Atlantic."

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