Breakthrough

Weather Forecast

Nature's Design: The Barrier Beach Cycle

From "Breakthrough: The Story of Chatham's North Beach"

On a clear day, the view from the lookout at the Chatham Lighthouse Beach overlook reaches to the almost indiscernible thread-like line where ocean meets sky, where never-ending blue hovers above darkly reflective water, cut occasionally by the ghostly whitecap of a wave or the hazy outline of a passing ship. It's one of the most spectacular views on Cape Cod.

Nowadays, though, eyes seldom stray much beyond the scene that lies just off Lighthouse Beach. The Atlantic waters churn and roil as the tide ebbs and flows through a two-mile-wide inlet, hypnotizing, furious, beautiful. Nauset Beach — North Beach after it crosses the Chatham town line — once stretched clear across what is now open water, something people visiting the overlook for the first time often find difficult to believe. But through a process as old as Cape Cod, the barrier beach has been violated, ravaged by nature. And still it appears, to the observer leaning against the ever-present clammy breeze 35 feet above the beach, to remain in the grip of nature's chaotic fury.

But there is order here. Every wave has its purpose, every tidal flat straggling off the southern tip of North Beach like a mini-archipelago fits into the scheme of the barrier beach cycle.

First described in detail by Professor Henry Mitchell in an 1874 report to the U.S. Harbor Commission, the Chatham barrier beach cycle consists of a 100- to 150-year-long process of beach construction and destruction, of migrating inlets and catastrophic erosion, illustrative of nature's power, logic and consistency. It's also a story inexorably linked to Chatham and its people, whose homes and livelihoods have over the years been at once dependent upon, and at the mercy of, the beach and the sea.

To understand the relationship between Chatham and the beach, it's necessary to look first at the geology and geological processes underlying Cape Cod as a whole, and the barrier beach system in particular.

As you stand at the Chatham Lighthouse breathing the salty ocean air and drinking in nature's handiwork, imagine yourself 40 miles to the east. Around you the dark ocean swells and dips, the only sounds the piercing scream of the gulls and the wet slap of sea against hull. If you sever Cape Cod from Massachusetts and make it disappear, the spot where you stood, with the lighthouse behind you, would be equally wet and lonely. The peninsula of Cape Cod juts 40 miles eastward into the Atlantic from the continental United States, taking a radical 90-degree turn northward at Chatham, and continuing another 35 miles or so to Wood's End, at the tip of Provincetown.

Which leaves Chatham, at the Cape's elbow, "a veritable town at sea, lying farther oceanward than any other town in the United States," observed Chatham native George "Chart" Eldridge, the 19th century hydrographer who founded the Eldridge Tide Charts, on which mariners have relied for more than a century. While there are points in Maine that are farther east than Chatham, no single community, not even our southern neighbor Nantucket, reaches as far, as tentatively, into the waiting arms of the Atlantic.

And embrace Chatham the ocean does, surrounding it on three sides with waters of different temperaments and personalities. To the south, Nantucket Sound's warm, gentle fingers caress the shoreline of West and South Chatham; to the north, the 7,285-acre Pleasant Bay, one of the largest, most productive and fragile estuaries in Massachusetts, and the Muddy Creek inlet enclose Eastward Point and Chathamport; flanking the eastern shoreline from North Chatham to Morris Island is Chatham Harbor; and just beyond the narrow spit of North Beach, the cold Atlantic.

Chatham was left in this precarious position after the ice sheets of the Wisconsin glacier retreated about 15,000 years ago. Before that, Chatham and the rest of the Cape had, for millions of years, been part of the northern edge of the exposed Atlantic Coastal Plain, now the submerged Continental Shelf, once an expanse of low-lying land which extended some 200 miles east of what is now the Outer Cape. During the Pleistocene Epoch, vast glaciers, more than a mile thick in places and originating in what is now Labrador, slid down to cover much of North America, carrying with them mineral debris dredged up along the way. After thousands of years the climate began to warm, and the glaciers retreated, carving furrows in the landscape and depositing their cargo of rock and sand and soil as they went.

The melting glaciers formed three ice bodies over what was to become Cape Cod: the Buzzard's Bay, Cape Cod Bay and South Channel Lobes. The Cape Cod Bay Lobe, to the north of Chatham, and the South Channel Lobe, to the east, left behind two deposits known as the Harwich and Nauset Heights outwash plains. Outwash is distinguished from the hilly boulder and gravel moraine deposits left by glaciers to the north and west, also referred to as glacial till, by its gently sloping, structured terrain composed mostly of gravelly sand. It is these glacial deposits, sculpted atop the older clay and rock of the coastal plain, which form the hooked, bent-arm landscape of Cape Cod. (The distinction between outwash and moraine becomes important later on in this story in determining the applicability of state laws prohibiting seawalls on dunes, i.e., outwash).

The area's numerous kettle ponds, bays and inlets were formed by stranded glaciers which melted in pits and furrows left by the retreating ice. As the glaciers melted, there was a corresponding rise in sea level (some 400 feet in 14,000 years), which filled the remaining gashes in the landscape, creating the inner shoreline. Wind, ocean waves and currents, in turn, ate away the newborn upland. Those forces, 3,000 to 4,000 years ago, created the Cape's major sand spits and dunes: the Province Lands, Sandy Neck, Monomoy and Nauset.

Which brings us, in geological terms, into the present. The smooth convex curve of Nauset/North Beach, when in one piece, extends at its longest 14 miles from Orleans to Chatham; Monomoy, the system's southern extreme, continues another eight miles. At times, the two have been connected. Usually, that happens after a breach in the barrier beach to the north, so that there is rarely, if ever, one continuous beach from Orleans to the southern tip of Monomoy.

As a barrier beach, North Beach shelters Chatham's mainland from the ocean's direct force, creating a stable inner shoreline and a relatively safe and calm navigable deep-water harbor. Barrier beaches are common throughout the eastern United States and are defined as low sand dunes separated from the main coast by a body of water. They take on various configurations: A barrier spit is joined to the mainland at one end (in rare cases, both ends), like North Beach in its most familiar form; a barrier island, as its name implies, is not connected to the main shore at all. Perhaps the best known barrier beach is Cape Hatteras, in North Carolina, a 180-mile-long series of barrier islands and spits running the length of that state's coast. Various barrier beaches can be found on the Cape and Islands, including Sandy Neck in Sandwich and Barnstable and Great Island in Wellfleet, though the Nauset system is by far the largest and most dynamic.

Whatever their shape, barrier beaches are by definition unstable, shifting land forms dependent on the wind and tide for their sustaining component, sand. The Nauset system looks 25 miles north to the imposing coastal cliffs of Truro, Wellfleet and Eastham for the sediment that feeds it, transported by wave and tidal current action (littoral drift is the scientific term) and deposited, like a sculptor applying layer after layer of clay, at the southernmost tip of the barrier beach.

The erosion rate of those cliffs is well-documented. When it was built in South Wellfleet in 1901, the transmitting and receiving station from which Guglielmo Marconi sent the first wireless trans-Atlantic message stood more than 300 feet east of the present shoreline, where there is now only the churning waters of the Atlantic. Erosion forced the station’s relocation, in 1914, to a more stable location near Ryder’s Cove in Chatham. At Truro's Highland Light, wind and wave action carves out about three feet of upland a year, and at Nauset Beach in Eastham, the shoreline recedes at a rate greater than five feet annually. At both those locations, massive public works projects were necessary in the mid-1990s to move both the Nauset Lighthouse and the Highland Light back from the shore due to encroaching erosion. But Truro, Eastham and Wellfleet's loss is North Beach's gain. Victor Goldsmith, in his 1972 doctoral dissertation on the Nauset system, wrote that the Outer Cape constitutes "one of the largest known volumes of sediment transported by longshore drift." Dr. Graham Giese, in his 1978 report on the barrier beach, put the amount of sand carved from the cliffs and carried southward at 300,000 cubic yards per year; a lot of sand, enough to fill a dozen football fields 15 feet high. This translates to a growth rate for North Beach of about two miles every 20 years as sand is deposited at the beach's terminus.

[Part 2]