A Sliver of Sand
From the air the great curled arm of Cape Cod looks like a mere film of sand, a whimsical momentary shape floating on the vast ocean around it. Its flimsy fabric appears torn and rent by hundreds of holes, large and small, and dozens of slits at the edges, where the water shows through. So sheer and vulnerable does it appear that it seems as if the slightest push might sink it beneath the sea.
This somewhat fanciful impression nonetheless contains several grains of geologic truth, for water, in its various guises, permeates the Cape’s past, present, and future. Created by the frozen water of vast glaciers, shaped today by the water of tides, waves, currents, and storm surges, this prominent hook of land is destined to succumb at last to the steadily rising waters of the sea—all in the merest flick of geologic time.
Some 75,000 years ago, when the Earth’s climate entered a cooling period, the most recent of the vast continental ice sheets, known as the Laurentide, began to form across eastern Canada. As it spread and thickened, much of the oceans’ waters became trapped in its mass, lowering sea levels by several hundred feet. The visible bulk of Cape Cod is primarily the work of the Wisconsin Stage Glacier, a towering wall of ice 10,000 feet thick that moved south over New England some 25,000 years ago. Grinding forward in rounded fronts, or lobes, the ice sheared off the tops of mountains, gouged huge valleys through granite hills, and plowed up tons upon tons of rocks, material, and debris from what had been the floor of the sea.
Advancing, hesitating, and advancing again, the glacier moved as far south as Long Island, Block Island, Martha’s Vineyard, and Nantucket. Then, as the climate warmed, the front edges of the glacier began to melt; the ice sheet retreated north of the present outline of Cape Cod, dropping rocks and large chunks of ice as it went. Then, as cooler weather returned, it paused, and, as the flow of ice exceeded the rate of melting, the glacial lobes once more advanced. This time they pushed enormous amounts of drift material across the face of the Upper and Lower Cape, creating the Elizabeth Islands in Buzzards Bay and the rocky, morainal hills on the western and northern sides of the Upper Cape.
When the glacier melted, it left behind huge rocks, known as erratics, scattered on the landscape.
As the glacier began its final withdrawal about 18,000 years ago, water from the melting ice carried and sorted finer material, forming the gently sloping southern and interlobate outwash plains of the Upper and Lower Cape (see [pages 26-27]). Braided meltwater streams covered the ice chunks that the retreating glacier had dropped in thick, insulating layers of outwash material. Eventually, perhaps centuries later, the buried ice melted and the glacial debris above it sank, creating the hundreds of kettle holes that are characteristic of so much of the Cape’s topography.
As the great ice sheets melted, the sea level began to rise, forcing the Cape’s fresh groundwater upward. When the freshwater level intersected with these kettle holes, the Cape’s numerous kettle ponds, so clear and deep, came into being. In some places these meltwater deposits and kettle holes form a highly irregular landscape of hills and hollows, such as the “kame and kettle” fields of Eastham, which can be seen on the bike trail from the Salt Pond Visitor Center to Coast Guard Beach.
Farther north a prominent series of east-west valleys cross the high plains of Wellfleet and Truro, separated by the so-called “hogback” hills of Truro. Most of these valleys only partially cross the Lower Cape. An exception is the Pamet River Valley, which traverses the entire forearm of the Cape, separated from the ocean at its eastern end only by a fragile line of dunes that is sometimes broken through by major storms.
For many years geologists believed these valleys were carved out by glacial meltwater streams, but a more recent theory suggests a different origin, based on a phenomenon known as “spring sapping.” Spring sapping occurs when water emerges at the surface of a plain to form a spring, or seep, which then erodes back up the plain toward its head. There is evidence that during the final period of glacial retreat a large freshwater glacial lake existed to the east of Cape Cod. The surface of this lake may have been as much as 80 feet above present sea level, providing a powerful head of water that may have leaked through the porous outwash material of the Lower Cape, producing springs that created the valleys we see today. However they were formed, most of these valley beds are dry today, or else they carry only the small, sluggish streams that constitute Cape Cod’s “rivers.”
Kettle ponds formed over time as underground freshwater filled glacial depressions. Today the life in these ponds can be quickly affected by humans.
After the glacier’s final withdrawal, Cape Cod was only a rough sketch of its present streamlined form. Its moraines, high tablelands, valleys, and kame fields stood high and dry amid the surrounding coastal plain that stretched a hundred miles to the south and east, as far as the present-day Georges Banks.
The sea, however, continued to rise and advance, gradually filling the Gulf of Maine and covering the continental shelf. It probably reached the edge of the glacial Cape some 5,000-6,000 years ago. Now the rough-hewn shapes left by the ice began to undergo a process of planing, smoothing, elaboration, and elongation under the more subtle hands of the sea. Currents, tides, and storms began to chew away at the outer shores of the Lower Cape, creating in time what is surely the most impressive feature of the Seashore, and perhaps the quintessential Cape Cod landscape: the great marine scarp, or sea cliff, of the Outer Beach.
Stretching some 15 miles from Coast Guard Beach in Eastham to Head of the Meadow Beach in North Truro, this curved headland presents a nearly unbroken, undulating bulwark of bold, eroding bluffs, composed of clay and sand and ranging in height from 30 to more than 170 feet above the beach. From South Wellfleet to North Truro the smooth rim of the sea cliff is marked by a half-dozen pronounced dips or “hollows,” which are the eroded cross-sections of relict valleys. These hollows were later to play an important part in the human history of this beach.
To the casual observer the cliff face appears uniform, lying at a general “angle of repose” of some 27 degrees to the horizon. But look closely and you will see that, as the Colorado River has done through the Grand Canyon, the sea has cut open the geologic book of the Cape’s history, exposing thousands of years of history. Alternating layers of till—rock debris deposited by the ice—meltwater-deposited sand and gravel, and clayey silt tell of the glacial advance and withdrawal, of inundation and ebb by the sea. Large outcrops of blue clay, such as the 25-foot thick “Clay Pounds” just north of Highland Light, are the result of glacial lake sediments deposited during the last deglaciation.
Low tide bares a wide expanse of sand patterns and tidepools at Coast Guard Beach.
The ocean also invaded parts of the land, creating estuaries and embayments at the mouths of these glacial valleys, such as those at Pamet Harbor and Blackfish Creek. Several of the Cape’s “salt ponds,” such as the one in Eastham below the visitor center, were originally freshwater kettle ponds that have been breached by the rising sea.
As Cape Cod was being smoothed, slimmed, and invaded by the rising sea, it was also being lengthened. Like a sculptor working in clay, the ocean currents took much of the eroded cliff material and, carrying it both north and south, created the elaborate forms of the barrier beaches, barrier islands, and sand hooks that give the Outer Cape its characteristic filigreed coastline. Monomoy Island, North Beach, Nauset Beach, Coast Guard Beach, and Jeremy Point are some of the more prominent of these post-glacial landforms, enclosing such important estuaries as Pleasant Bay, Nauset Harbor, and Wellfleet Harbor. Among the more unusual formations are the tombolos of outer Wellfleet Harbor: the series of short sand beaches that connect Bound Brook, Griffin, Great Beach Hill, and Great Islands.
Of all these sea-spawned parts of Cape Cod, however, the most impressive and extensive is undoubtedly the Provincetown Hook. These 3,000 acres of dunes at the northern tip of the Cape form a broad recurved spit of sand that encloses Provincetown Harbor, one of the finest deepwater harbors on the East Coast and the initial port for the Mayflower Pilgrims in 1620. Some oceanographers believe that the hook began to form as much as 6,000 years ago and has built up in a series of roughly parallel ridges, or dune lines, widening out into the ocean.
In the protected bays and inlets behind these elongating fingers of barrier beaches and islands, salt marshes—one of the Cape’s most characteristic and important ecosystems—began to form 4,000 to 6,000 years ago. Composed of a few species of salt-tolerant grasses, primarily the stalky cord grass (Spartina alterniflora) and the finer salt hay (Spartina patens), these green salt meadows of the sea built slowly on the accumulating sediment deposited in protected areas of water by the tides and land runoff. Gradually, as the sea rose relative to the land, the marshes raised and spread themselves on a platform of their own decay, forming thick beds of peat underneath them. As the climate continued to warm, the Cape’s woodlands evolved from boreal forests to the mixed pine-oak woodlands we see today.
Pitch pine is the most common tree on Cape Cod and the only species of native pine that grows in the National Seashore. It survives on well drained glacial sediments and stable sand dunes and is very fire resistant. In this stand on Great Island, the undergrowth is primarily bearberry.
As the Cape’s post-glacial environment grew more diverse and complex, so did the culture of the people living on it. The first Native Americans on Cape Cod are now thought to have arrived at least 9,000 years ago. By the late Archaic Period, starting about 5,000 years ago, local Indian groups had developed a seasonal pattern of movement based on multiple resources. During the warmer months they settled on the shores of bays, marshes, and fish runs, trapping birds and collecting herring and shellfish. In winter they retreated inland to the more protected forested shores of ponds and other wetlands.
By the beginning of the Woodland Period, about 2,500 years ago, Indian settlements had grown even more numerous, larger, and more sedentary. About 800 years ago agriculture and a variety of new materials and tools had been introduced. One of the most important of these “tools” was fire; with it the Cape’s Native Americans changed the face of the land.
Many early accounts attest to the extent and scale of the Cape’s original woodlands. Even at Provincetown, which must have always been the most barren area of the Outer Cape, the Pilgrim leader William Bradford observed “The whole countrie, full of woods and thickets, wooded with oaks, pines, sassafras, juniper, birch, holly, some ash, walnut, the wood for the most part open and without underwood, fit to go or ride in.”
Archeologists now believe that the Cape Cod Indians may have practiced a form of low-level woodland management, burning underbrush, or wooded ridges, to provide browse for game and to make hunting easier. Such burns may have promoted the Cape’s characteristic pine barrens, tracts of open woodlands composed primarily of pitch pine, a tree adapted to periodic fires.
Some glacial lands, now vanished, still existed in historical times. There are many early references, for example, to Ile Nauset, or Nauset Isle, a point of land that lay off Nauset Beach, perpendicular to the coastline. It may have formed part of Cape Mallebarre, the place of “dangerous shoals and roaring breakers” that turned back the Mayflower from its intended destination of Virginia. Nauset Isle had sunk beneath the waves by the 18th century, but another piece of early glacial real estate survived much longer. In the late 19th century, Billingsgate Island, off Jeremy Point in Wellfleet, was a flourishing 60-acre fishing community with livestock, a schoolhouse, and a lighthouse. By 1915, however, the island had been abandoned, and by 1942 it had vanished, the victim of gradual erosion by currents, storms, and rising sea levels. Today, at low tide, one can view the remains of this Wellfleetian Atlantis from the southern bluffs of Great Beach Hill: an extensive spread of granite boulders brought over on ships as riprap in a futile attempt to stem the tides.
In Capt. Myles Standish the Pilgrims had both a military and temporal leader. He helped found the Plymouth Colony, led a group that bought the colony from London investors, and served as assistant governor and treasurer for 5 years. Metacomet, or King Philip, shown in an engraving by Paul Revere, was killed leading the Wampanoags in an unsuccessful war concerning land disputes with the English settlers in 1676.
To get some idea of the scope of erosion on the Outer Beach, consider this: in 1990 an ancient prehistoric site was uncovered at Coast Guard Beach; archeologists have estimated that at the time of its occupation, nearly 9,000 years ago, it was five miles inland. More recent evidence of erosion can often be observed on the Seashore’s ocean side. At Nauset Light Beach, a circular brick foundation from one of the former “Three Sisters” lighthouses (replaced in 1923 with the present single light) is frequently uncovered in winter at the base of the cliffs, having survived a 50-foot slide to the beach. Farther north, at the Marconi Site in South Wellfleet, Guglielmo Marconi constructed his original transmitting towers in 1901-1902, set back 165 feet from the edge of the cliff. Today only two of the foundations remain; the other two have fallen into the sea.
Few things remain in place on the edge of the cliffs or on the dunes. They either move or disappear. Cape Cod Light, first built in 1796, has been replaced twice; the current tower sits some 600 feet back from the site of the original one, though only a little more than 100 feet from the present cliff edge. The present Eastham Coast Guard Station, built in 1936, is a successor to the first one, which succumbed to beach erosion. When the Seashore was established in 1961, more than 80 cottages existed on its barrier beaches. Today, as a result of subsequent storms, less than one quarter of them remain.
Logs and other objects, including the remains of old shipwrecks, are frequently uncovered by eroding dunes and beaches. During a dramatic storm, while he was staying in the Outermost House in the 1920s, Henry Beston described how the blackened skeleton of an ancient ship that had been buried in a dune for more than a century “floated and lifted itself free ... thus stirring from its grave and yielding its bones again to the fury of the gale.”
Fall and winter storms often develop quickly and tear away at the shorelines, removing sands from one place and depositing them elsewhere.
One survivor of this coastal erosion is the Old Harbor Life Saving Station. Now a maritime museum at Race Point Beach in Provincetown, it began life in 1897 twenty miles to the south on Chatham’s North Beach. In 1977, in the face of imminent destruction, the station was cut in half and floated on two barges to its present site.
During the summer, the beaches of the Outer Cape present a generally peaceful and benign aspect. A wide, gently sloping shelf of sand lies between the base of the sea cliffs and a rhythmic, moderate surf. The summer shoreline’s peaceful countenance encourages the illusion that all this change and rearrangement of shoreline lies in the settled past. There is little indication to the summer visitor of the ferocity, violence, and transformation that visit this coast in the “off-season.” But if one returns in late autumn, when the prevailing winds shift to the north and the east, when the first northeasters of the season begin to chew away at the wide summer beach, replacing it with a short, steep winter berm, one begins to have a sense that this is still a land in the making, that, as Henry Beston observed, “Creation is here and now.”
In winter the ocean storms claw into the base of these cliffs, undermining them. Along some stretches erosion is gradual, with little rivulets of sand running down the cliff face into the sea. At other places, especially where there are large deposits of clay, the process can be dramatic. Whole slabs of the marine scarp may shelve off at once, and a single stretch of cliff may lose 30 or 40 feet in one storm. In still other areas the beach appears to be accreting, with wide terraces of sand covered with beach grass building out from the cliff base. But overall the Outer Beach continues to erode, losing an average of three feet a year.
On the barrier beaches the erosion process is somewhat different, though the overall effect is also retreat. Barrier beach dune lines are dynamic systems. That is, they retreat and maintain themselves by moving with, rather than resisting, the ocean’s power. Normally the foreslopes of the dunes flatten out during a severe storm, presenting a less steep face to the waves, which helps to dissipate their force. Meanwhile wind and occasional storm surges that break through the line carry sand into the estuary or marsh behind the dunes. These deposits are gradually colonized by beach grass and other beach plants, which begin the process of building up another dune line as the foredunes continue to erode. Evidence of this gradual retreat can be observed by the occasional emergence in front of the present dune lines of peat ledges, the remains of a salt marsh or freshwater bog that once lay behind a former line of dunes. In a healthy system and under normal conditions a barrier beach “rolls over on itself” in a smooth progression landward.
On occasion, however, even this process is overwhelmed by an unusual manifestation of the sea’s power. One such manifestation was the Great Blizzard of February 6-7, 1978, called “The Storm of the Century.” Carrying 15-foot tides and hurricane-force winds, this storm rearranged many parts of the Cape’s shoreline. Monomoy Island, for example, was severed in two, and remains so today. But nowhere were the effects more dramatic and visible than at Eastham’s Coast Guard Beach. Storm surges breached the dune line, flattening 90 percent of the dunes themselves, carrying off most of the beach cottages, including Henry Beston’s Outermost House, and totally destroying the Seashore’s bathhouse and large parking lot.
Provincetown has always been the Cape community that has had to contend most with change. During the 19th century the moving dunes of the Province Lands threatened to bury its houses and silt up its vital harbor. Subsequent erosion control and beach grass plantings have so far kept the dunes at bay, but a more implacable force may now be threatening the town.
Over the past few decades oceanographers have observed an acceleration in the rate of sea-level rise, possibly the result of global warming. The sea may now be rising as much as one foot every century, which on low shorelines translates into a loss of 100 feet inland. Nowhere on Cape Cod does thick settlement lie so close to the shore as along the low, narrow streets of Provincetown. If present rises in the level of the sea continue, or, as seems likely, increase, the ocean may well claim this ancient fishing community before the dunes do.
Meanwhile the bulk of the Provincetown Hook continues to expand outward into the sea. The dangerous Peaked Hill Bars represent, in current oceanographic theory, the next ridge of Province Lands dunes in the making, rising gradually from the sea. But regardless of such gains, or the pains taken by humans to stem the loss of land from the sea, the Cape is inevitably losing more than it is replacing. Oceanographers estimate that for every five acres of shoreline lost to erosion, only two are replaced with new land in the form of barrier beaches or sand hooks. There is little doubt that the Cape’s ultimate fate is to return to the sea that spawned and shaped it. At current rates of sea-level rise, Cape Cod has at best only another five to six thousand years before the Puritan preacher Cotton Mather’s prediction comes true, and “shoals of codfish be seen swimming on its highest hills.”
Salt Marsh
Salt hay and cord grass
Sea stars
Lobster
Hermit crab
Moon snail
Fiddler crab
Anemone
Moon jelly
Sea-lavender and honey bee
Bay scallop
Eelgrass
Rock crabs
Northern diamondback terrapin
Glasswort, or salicornia
Sea robin
Sea lettuce and mussels
Schools of silversides, about 3 inches long, dart through shallow waters feeding on plankton. They in turn are fed upon by other marine life and birds such as gulls and terns.