Nature Notes: Coastal Lingo 101
While we see if Hurricane Matthew, a humdinger of a storm in the Caribbean Sea as of Monday, comes to us or spins off toward Europe, it’s a good time to go over some of the coastal terms that we have all heard from past experiences, but may have faded into the non-recall department. There is no better place to review them than on both sides of the South Fork, especially with respect to Matthew and the northeaster season coming up.
Whether Long Island is a true island or not, it owes most of its origin and features to the Wisconsin glaciation, which landed two times in the last 25,000 years or so. However, the post-glacial era has wrought a slew of geomorphological changes, so if we were able to Google a photograph of Long Island as it looked 10,000 years ago we wouldn’t recognize it.
Its aspect is very different today, particularly because it’s not underpinned by bedrock the way New England and the rest of New York State, including New York City, are, but composed of aggregates of loose soil, sediments, gravel, and large rocks. The large rocks are not as mobile as the smaller stuff, but they do fall out of bluffs onto the shore on both sides of the South Fork, particularly in Montauk. They move only “relatively,” i.e., as the coastal bluffs continue recede, as they have been doing for thousands of year; the biggest rocks, or “glacial erratics,” find themselves situated deeper and deeper in the sea.
Take Lionhead Rock in the bay off the hamlet of Springs, for example. It started out in the landmass east of Three Mile Harbor and ended up in its present spot as the bluffs west of Hog Creek wore back toward the south. All of the large boulders strewn along the shores of the Peconic Estuary were once rooted in the fast land. In Montauk and Noyac there are loads that still are. Take a peak at Sag Harbor’s waters on the seaward side of the 114 bridge at low tide and you will see the many boulders deposited in the harbor as North Haven’s bluffs wore back and the harbor waters rose.
If you were to take a peek along the Long Island Sound bluffs in Mattituck and Peconic east of Mattituck Creek it would remind you of Montauk east of Ditch Plain. The latest research by coastal geologists suggests that some or all of these big stones came from the bottom of Long Island Sound as the glacier advanced, helping to created the sound’s basin, which stretches from the Bronx in New York to Block Island Sound between Orient and Montauk Points.
As the glaciers melted, water ran out to the ocean, later to the Peconic Estuary. You don’t find any boulders in the ocean’s edge west of downtown Montauk because they have yet to wash out of the bluffs west of Montauk. You don’t find any on both sides of the Napeague isthmus because the isthmus didn’t exist until well after the glacial sheet retreated and erosion from both sides of Napeague Harbor, which was open on both ends, drifted onto the bottom, raising the isthmus above sea level and closing it off on the ocean side. Don’t look now, but it could open again in the next 50 years or so.
The famous Napeague ocean dune field owes part of its existence to the sedimentary materials moving westerly in the ocean’s long shore drift from east to west, but some of it came from the isthmus as it receded to the north. For a thousand years or more the only vegetation of the isthmus was beach grass and salt marsh grasses. Now the isthmus is half covered with beach plums, shads, pitch pines, and other woodies.
A late 1700s nautical chart shows Napeague Harbor opened widely to Gardiner’s Bay. There was no Hicks Island and no Goff Point on the other side of an east inlet. Over the millenniums, the harbor has been kept open by northwesterly winds blowing sand onto the bay’s east shores, then up into the fast land of Hither Woods, creating the famous Walking Dunes that are creeping slowly to the south-southeast at a few centimeters per year. The lead-in one has been stopped in its tracks for the last hundred years or so just north of the Long Island Rail Road tracks, which were pushed through in the 1890s.
The 1938 hurricane breached the Napeague isthmus and others, such as Carol in 1954, have breached it since.
The array of remnant coastal ponds along the south shore between Shinnecock Bay and the Double Dunes east of Hook Pond in East Hampton Village were probably all connected in one big water body, which extended along a broad front. They were gradually isolated by onshore dune processes that created the Double Dunes and the lower dunes stretching from East Hampton Village in the east all the way to Agawam Lake at the foot of Southampton Village.
Napeague and the rest of Amagansett’s oceanfront grew out into the ocean for hundreds of years as sands came on shore and blew up into the dune field, creating several rows of dunes, the oldest of which have come to rest on the north side of Bluff Road and the farm fields and building lots to the east of Indian Wells Highway. Thus, the name Double Dunes is a misnomer, as there were also tertiary and quaternary dunes created early on. A new primary dune may be in the offing should more sand be deposited on that stretch of beach, but it is highly unlikely with the current accelerating sea level rise.
Where there are north-south trending “valleys” along the ocean shores — such as that through Two Mile Hollow Road northward from the ocean parking lot in East Hampton Village to Further Road, then north again by way of Cross Highway to Montauk Highway — coastal storms through the ages have blown sand through them all the way to north of the Long Island Rail Road tracks, where you can still find dune sand overlaying much older soil.
In western East Hampton Village the same phenomenon took place over time; sand moved all the way north of Montauk Highway, for example, to where there is a ridge of high land just west of the Route 114. Amagansett’s shoreline and that to the west have hardly lost any sand in the last 50 years or so, while the Montauk Peninsula’s Fort Pond Bay shore west of the west groin to Montauk Harbor has lost more than 300 feet since the 1930s as measured by the National Coast and Geodetic Survey from aerial photographs.
The Montauk Lighthouse, now a national historic landmark, was situated on Turtle Hill at the very end of the 18th century, more than 200 feet from the water’s edge. Today, the lighthouse stands less than 40 feet from the bluff on average. The loss of almost 200 feet of fast land since its construction, or about one foot per year, is used as a rule-of-thumb measure of the rate of coastal erosion in Montauk. That rate has been doubling rapidly. In some spots, for example Cavett’s Cove, where the bluffs are not protected by any sort of barrier, the landward edge is retreating at the rate of three to five feet a year. A mile west of Cavett’s Cove, a parcel that extended 340 feet to mean high water south from the end of South Surfside Avenue in 1928 was 220 feet from mean high water in 2013. In other words, the bluff line from Ditch Plain on the east to South Surfside in downtown Montauk has been eroding at an average of approximately 1.6 feet per year.
One merely has to visit by boat the south end of Gardiner’s Island to see Cartwright Shoal, called Cartwright Island on some maps, to see how sea level rise is drowning bits of land in the Peconics. The spit to Fort McKinley, now a pile of rubble, on the north end of Gardiner’s Island has long disappeared under water. Spits that go under become sandbars. There are other sandbars, which lay off the ocean’s and bays’ shores, that come and go. The one in Block Island Sound that was a few hundred yards off the beach for several years has disappeared. Most of those along the ocean shore have either been carried off by coastal storms or come ashore.
The so-called barrier beach running from the west side of the Shinnecock Inlet on and off all the way to the Rockaways of New York City has been progressing, or “rolling over,” northward and the only way to stop it in its tracks is to pour more and more sand on it, most of which is pumped on shore from very large dredging barges as is happening now under the auspices of the Army Corps of Engineers along much of the barrier beach’s length.
As you can see, we are coming and going and almost powerless to stop coastal erosion completely. But with the threat of increasing erosion and sea level rise, if we stop dumping sand on the beach to replace what is lost, Long Island’s future is dim. The only thing protecting Montauk’s downtown area, with its shops, motels, restaurants, and office buildings, is the wall of motels, condos and other buildings situated at the extreme edge of the strip of land a few feet above sea level, if that Maginot Line were to fail, the rest of the downtown area would be up for grabs.
Larry Penny can be reached via email at [email protected].