The changing shoreline on Martha's Vineyard variously fascinates, startles or horrifies people, depending on where they live or own property. The strongest supporting images of erosion are provided by destruction of buildings located at the water's edge, such as lighthouses and Worlds War II military bunkers. Among the latter, a concrete bunker (part of the Katama Naval Air Station target track) once 180 feet from the shore at South Beach in Edgartown was last seen far offshore, drowned in the surf. The associated rate of shoreline retreat comes to about 12 feet per year.

Another massive concrete bunker constructed near the cliff edge in Aquinnah in about 1940 toppled over and presently lies on the beach below. (This bunker was one of 10 fire control points serving Battery Gray at Ft. Church on Sakonnet Point, whose two 16-inch guns had a range of 25 miles.)

Only one of the five lighthouses on the Vineyard, Cape Pogue Light, has had to be moved back from the eroding shoreline. This lighthouse has been moved as many as five times since it was built in 1802, most recently in 1987 when the entire wooden structure, gutted of plaster and lath, was picked up by helicopter and moved to its present site, safely inland. The shoreline at the point on Cape Pogue has eroded about 218 feet since 1887 at a rate of 3.8 feet per year, which happens to be the highest rate of erosion on Cape Pogue.

The other lighthouses, through luck or good planning, were sited at safer locations. The site of Edgartown Light in fact has experienced accretion since it was first erected in open water in 1828 (access was by catwalk). The present structure, moved from Ipswich in 1939, stands at the original site, now transformed by deposition into a sandy point at the mouth of Edgartown inner harbor.

Map Evidence

The rates of erosion around the Island have been systematically estimated by comparing old maps with new ones. A long time span is needed because the thickness of the line demarking the shoreline on an ordinary topographic sheet is eight feet wide on the ground. The oldest high quality map of the Island is that of DesBarres, a British cartographer who mapped the Island in 1776, in some cases even marking individual boulders that can still be located today. A copy of this remarkable map can be viewed at the Martha's Vineyard Historical Society Museum in Edgartown.

But the oldest maps and charts of the area using standardized, comparable methods is the series of U.S. Coast and Geodetic Survey maps beginning in 1844. Detailed calculations of shoreline change have been mapped for each coastal section of Massachusetts (available on Internet at There are several problems with this approach to determining shoreline change, but viewed with caution the maps are still useful.

On Martha's Vineyard, highest rates of shoreline change border the south shore, where the thundering onslaught of waves from an infinite North Atlantic fetch can beat sand into a mobile slurry. On these sandy shorelines typical rates of retreat are five to eight feet per year. The rate more or less uniformly decreases toward the west reaching minus 2.5 feet per year near the cliffs at Nashaquitsa and Wequobsque.

Squibnocket Point consists of boulder-studded, resistant sediments whose retreat is only 1.1 feet per year. Squibnocket Beach and dune field, shown with an open inlet on the DesBarres map, has retreated at 4.1 feet per year over the mapped period, encroaching into Squibnocket Pond. Since an artificial opening (Herring Creek) of unknown date connected Squibnocket Pond with Menemsha Pond, Squibnocket Pond has lacked the seasonal freshwater head needed for its inlet formation.

The cliffed shoreline from Zacks to Gay Head exhibits a retreat of about 1.2 feet per year. Erosion at Aquinnah has been variable but averages only 1.1 feet per year. Like Squibnocket Point, the boulder field residue left in the surf zone stands to armor this point from rapid erosion, despite appearances to the contrary. (Noman's Land cliffs on its south shore are retreating at about the same rate as Squibnocket or Aquinnah, roughly 1 foot per year).

Sediment lost from Aquinnah has nourished its more sheltered north shore bordering Vineyard Sound, with rates of accretion there averaging 1.2 feet per year. Erosion along the Vineyard Sound shoreline north of Menemsha inlet is quite variable, but generally averages about 0.6 feet per year of retreat, extending up to West Chop where erosion decreases by half. Shoreline structures at Lake Tashmoo, West Chop and in Vineyard Haven harbor have locally trapped sand.

South from East Chop, where historical maps indicate shoreline accretion, the shoreline has been subject to human modification with sea walls, jetties and groins. The associated interference with natural littoral drift of sediments has been associated with causing strong erosion down-drift of this stretch, averaging as high as 4 feet per year near Farm Pond.

Sengekontacket Beach, however, has been comparatively stable and in places has shown the most rapid rate of accretion of any site on the Island.

The glacial sediments making up the point at Cape Pogue have displayed a comparatively rapid rate of erosion, although the barrier beaches that form the margins of Cape Pogue Bay have been remarkably stable over the years, with variable erosion and accretion depending upon the specific site.

On Martha's Vineyard the greatest rate of retreat of any point consisting of glacial sediments is at Wasque, where the evidence from maps indicates an average loss of nearly 5 feet per year.

The Numbers Game

Representing the Island as a triangle 20 miles long at the base and 9 miles across, shoreline recession of 8 feet per year along the south shore amounts to a loss of 19 acres or 0.034 per cent of the Island each year. Shoreline change is much less on sides of the Island facing Vineyard Sound and Nantucket Sound, perhaps as little as an average of 0.8 feet per year. The total amounts to 22 acres lost per year (0.036 per cent of Island area lost per year) or 1,650 acres (2.9 per cent) of the Island's total area lost in the course of a 75-year adult lifetime.

At a shoreline migration rate of 8 feet per year along the portion of the south shore bordering on Great Ponds, the overall loss in pond area is 6.6 acres per year or nearly 500 acres in 75 years. The overall loss in pond area occurs because the landward margins of the ponds show no evidence of significantly enlarging as the seaward margin encroaches from the south.

Erosion, Migration and Flooding

"Shoreline change" is not synonymous with "erosion." A typical barrier beach bordering a Great Pond, the one at Edgartown Great Pond, presently has an overall width of about 325 feet. If the estimated shoreline change rate of 8 feet per year resulted from net erosion, the beach would thin at that rate and would disappear after 40 years.

To the contrary, historical maps show these beaches are not thinning at all, and that the pond side of the beach grows at the same rate the seaward side is lost. This results from a "rollover" of sand from the seaward side to the ponds side and a resulting migration of the entire beach deposit northward. Thus, shoreline change in these barrier beaches cannot be considered erosion, or at least not net erosion, but rather represents beach "migration." The processes involved in northward beach migration at the Great Ponds are overwash during storms, sand transport by the wind and flood delta development in the ponds during active breaching events (inlet formation) — whether natural or artificial.

In contrast, along the cliff portions shoreline change does result from net erosion. Through erosion, these cliffs (Squibnocket Point, Nashaquitsa and especially Wequobsque) provide about 100,000 cubic yards of sand per year to nourish the south shore beaches. Erosion along Wequobsque was cited by the famous 19th century geologist N. S. Shaler (who founded Seven Gates Farm, West Tisbury and Chilmark) as possibly the greatest of any cliffed portion of the New England coast. Since the entire south shore is retreating, it is clear materials lost exceed materials supplied. The fate of this material is not entirely clear, but it probably maintains the Cape Pogue beach complex and feeds into the large Muskeget Channel ebb delta, of which Wasque Shoal is a part.

Shoreline change from flooding by sea level rise can in principle also be significant. The basic idea is that as water level rises against an inclined surface, the horizontal movement of the waterline itself will be related to the rate of rise as well as the angle of the surface. For a vertical wall, there would be no horizontal shoreline change. For a surface inclined at 45 degrees, a one-foot rise in water level will move the shoreline one foot horizontally. In fact most shorelines on Martha's Vineyard are much less steeply inclined than that, so the horizontal shoreline change could be much greater than the vertical rise of water level. For example, the land slope on Katama Plains in Edgartown is about 30 feet in 1.7 miles, measured from south of Mill Hill to the shoreline at South Beach. This represents an angle of only 0.197 degrees. For a sea level rise rate of 9.8 inches per century, which is the approximate rate observed at the tide gauge in Woods Hole, the shoreline change at South Beach resulting from flooding alone would be 236 feet per century, or 2.4 feet per year. Since the observed rate of shoreline change there is about 8 feet per year, flooding alone could only partially account for the observed change. This conclusion probably also holds for other Island sites which, in general, are more steeply sloped than Katama Plain.

Rising Sea Level

Rising sea level has other consequences that can be observed on Martha's Vineyard. Steve Ewing, a dock builder in Edgartown for 30 years, has worked on many of the shoreline structures in the inner harbor. He estimates the sea has come up about two inches in that time (which equals 6.7 inches per century). In replacing decks on some of the older structures, some more than 60 years old, he has had to raise the deck level by a few inches. In rebuilding the "low platform" (used for entering and leaving dinghies) attached to Walter Cronkite's dock, the new structure needed to be raised several inches from its original elevation. For Charles Erdman's dock, originally built in 1932, replacement pilings are now cut off a foot higher than the original ones so that eventually the entire dock surface can be raised. The owner complains that his dock currently floods more frequently than it did 68 years ago.

Similarly, the surface of some of the filled quays in Edgartown have been raised over the years. A newer top course of stone is visible at the Reading Room sea walls where the filled interior surface has been raised. The wooden Town docks at the foot of Main street are proposed to be raised by about six inches along with the parking lot surface when that project moves ahead. In each case tidal flooding of the surfaces has become more evident in recent years.

There is natural evidence of sea-level rise as well. In the vicinity of the cedar forest growing on Cape Pogue barrier beach, old cedar stumps can be found in the intertidal zone. These stumps could not have grown submerged in sea water and therefore must represent the remains of ancient trees killed when salty water flooded their habitat. Similarly, a pine stump in living position was recovered from the low-tide line near Job's Neck Pond on the south shore; and a red maple stump was recovered at a similar depth off the north shore. These stumps were carbon-dated at 400 to 600 years old.

Probably the best local evidence of recent sea-level change comes from tide gauges operated over long periods of time. A tide gauge at the Woods Hole Oceanographic Institution, located near the Steamship Authority ferry dock, has operated continuously since 1932 (daily observations can be found on Plotting average monthly sea level since 1932 gives a total sea-level rise of 6 5/8 inches, a rate of 9 3/4 inches per century (3/32 inch per year) at this station. It is notable that Mr. Ewing's estimate based on dock building is only off by an inch.

The Woods Hole tidal data also reveal large seasonal variations in sea level, amounting to about 5 1/8 inches annually from a high in late summer to a low in late winter. These fluctuations result from annual astronomical tides and possibly from seasonal changes in wind stress, temperature and salinity of coastal waters. Many years ago, at great effort, I measured this seasonal tidal constituent for a Rhode Island estuary. I mentioned the result to a local river man (whose dock held my tide gauge) and he told me he already knew that. He said the rock he stepped on to get into his boat in wintertime was always underwater during summer.

For perspective, there are many factors that affect water level on Martha's Vineyard, most of global significance as well. Some of the short-term variations such as storm waves are quite large and rapid. Tides and storm surges last hours or days. Changes resulting from melting glaciers or long-term temperature change in the ocean can be larger, but are slower in happening. Crustal movements resulting from loading and unloading of continental ice caps are another source. It is these changes that are the subject of greatest concern and speculation in the current debate on sea-level rise.


As indicated for Edgartown Lighthouse, several areas of the Island shore are currently enjoying accretion. Sengekontacket barrier beach north of the Big Bridge has grown seaward over 200 feet since the main jetty was constructed in the 1970s, contributing to the public beach recreation area, natural habitat and protection of the state highway. Accretion here amounted to about 8 feet per year until the jetty became filled. Similarly, the beach adjacent to the small jetty on the south side has grown significantly seaward. These changes reflect the effectiveness of the jetties in protecting the inlet and capturing sand on either side, and constitute real growth in economic value of this coastal setting.

At the other end of the Island, Lobsterville Beach and the associated dune field continues to build seaward at a rate of about 0.6 feet per year. This 178-acre land form, which constitutes the northern shore of Menemsha Pond, was created entirely from materials eroded from Gay Head Cliffs. Based on the current rate of accretion, the Lobsterville Beach complex would have taken 3,000 years to form. At both Sengekontacket and Lobsterville the enhancement of the shoreline in one place resulted from erosion of materials from other places. Elsewhere on the Island, many of the most valued recreational beaches were formed and are maintained by continuing erosion of adjacent lands.

Enigmatic Sites on Martha's Vineyard

At a few sites on the Island's complex shoreline, changes defy simple explanation. One such area is near Farm Pond in Oak Bluffs. Travelers along Beach Road can look out and see two jetties sitting isolated offshore. When they were built, these jetties were intended to stabilize the Farm Pond inlet and adjacent beaches. Along the side of the road there is evidence of Massachusetts Highway Department attempts to protect the road, also without apparent success. This area, which appears to be a transition zone, is the object of state study and long-term plan presently nearing completion. The loss of barrier beach and associated waterways has been rapid and without pattern.

Another enigmatic area is the coastal section forming the southern boundary of Edgartown's Katama Bay, from Wasque on Chappaquiddick westward along the Norton Point barrier beach) The historical beach dynamics of this area are described in a 1975 paper by the late Prof. Gordon Ogden who summered for many years on the Vineyard. A series of historical maps of this area are also reproduced in Appendix 1 of my 1998 report on Cape Pogue Bay. The barrier beach at this location has displayed extremely active variability. As depicted by DesBarres in 1776 this barrier beach slanted southeast from its present position, such that the end nearest Wasque (an inlet existed there at that time) was 2,700 feet seaward of its present position. In the 70-year span to 1846 the beach rotated counter-clockwise to become parallel to (but offshore from) the present coastline, the east end migrating 2,000 feet northward (28 feet per year). From 1846 to 1969 the entire section of beach migrated northward toward Katama Bay an average of 1,100 feet (9 feet per year).

In addition to migration and rotation, the beach has breached several times, opening Katama Bay to the Atlantic and to ocean waves. The breaching event seems to be associated with certain severe northeast storms and hurricanes such as in 1886, 1938 and 1954. The breachway tends to form toward the west end of Norton Point near Mattakesett, with the resulting inlet then migrating eastward over a period of years toward Wasque on Chappaquiddick. In some cases the inlet has actually migrated around Wasque Point, giving the impression that with time it could connect with Poucha Pond on the east side (no map has ever depicted this connection). With the barrier beach in this configuration, Wasque point has intermittently accreted southward.

Since 1969 a section of the former inlet channel "wrapping around" Wasque was cut off, resulting in an isolated, long oval lake in the beach at Wasque. Over the past decade this lake has filled in. A similar lake formation has been observed at Popponesset Beach on Cape Cod, suggesting a generic process producing these features.

During Hurricane Edna in 1954, Dr. Ogden was able to witness the formation of the breachway at Norton Point. Given the circumstances, he was fortunate to have survived this adventure. After the crest of the storm had passed, during which the barrier beach had been submerged beneath pounding storm surf driven by east southeast winds, Mr. Ogden walked out to Norton Point facing eastward. While the ocean tide had rapidly dropped, reexposing the barrier beach, the water level in Katama Bay was still very high, since its only existing exit was northward through the harbor.

All at once the beach sand level dropped along a low fault in the sand crossing the barrier beach. Mr. Ogden's feet sank deep into the sand when he attempted to walk there and he only narrowly escaped to make his retreat. It was if the saturated beach had become semi-liquid. Each thundering ocean wave moved more sand off the barrier. Within 30 minutes the waters of Katama Bay were flowing through, driven by the tidal difference, cutting an opening that grew to 300 feet wide within 30 minutes.

By the next morning the breachway looked as if it had always been there. Mr. Ogden's description is in many ways similar to Mr. Whiting's of the 1886 opening, notably, in both cases the inlet was cut by flow outward from Katama Bay.

Not all severe storms have breached Norton Point. Following Hurricane Bob in 1991, during which most of the barrier beach was submerged, I observed two small breachways that flowed for a day or two, but then healed shut. Several attempts to dredge artificial inlets have also been made here over many decades, most of which failed. The appearance of narrowness along parts of this barrier beach does not seem to indicate imminent susceptibility to breaching. Over the past few years recurrent predictions of imminent breaching based on that observation have been incorrect.

The Next Millennium

Many shocking predictions were made during the 1980s of projected sea-level rise. As we approach the year 2000, most predictions have decreased to values closer to what has been measured historically by tide gauges. In 1990 a National Research Council study estimated the rise would range between 20 to 40 inches by the year 2100. The federal Environmental Protection Agency currently predicts a rise of 10.2 inches by the year 2050 and of 21.7 inches by the year 2100 in southern New England (double the historical rate at Woods Hole). Many recent reports emphasize factors other than atmospheric greenhouse warming as significantly affecting sea level, such as land subsidence, wind effects and natural ocean oscillations.

At the EPA, predicted rate shoreline changes over the next century can probably be more or less extrapolated from what has happened over the past century. If sea-level rise doubles in rate, the impacts would not be disastrous.

In Chesapeake Bay sea-level rise over the past century has amounted to 16 inches, more than 1.6 times the rise at Martha's Vineyard (one estimate has sea level rising nearly four feet since Jamestown was settled in 1607). Although in the case of Chesapeake Bay there have no doubt been significant impacts, no dramatic loss of life or property has been attributed to sea-level rise. No headline news.

The impact of rising sea level will span much of at least two lifetimes, with more than ample time for society to make needed modifications to roads, docks and other infrastructure, which will need replacement anyhow. At present, however, structures and activities at the immediate shoreline will be subject to natural hazards. Use of low-lying areas then, as now, will require special caution.

The principal impact on Martha's Vineyard will be an increased shoreline recession along the south shore. This will result from more rapid submergence and from an increased erosion rate. Increased erosion will come about because the more rapid shoreline retreat observed in the east, compared with the west, is causing the south shore to rotate counter-clockwise. This rotation will cause the angle of wave attack to more strongly drive littoral drift toward and around Wasque.

A related consequence will be that openings to the Great Ponds will close more quickly as more active moving sand fills their entrances. The increased supply of sand rounding Wasque may serve to nourish the beaches at Cape Pogue, adding further stability to that bay.

There is some reason to fear for the salt marshes, such as in Poucha Pond. It is not clear their ability to grow upward will be sufficient to keep up with the faster rising sea rate. If not, they will be drowned and become shallow water aquatic communities.

Elsewhere on the Island, changes in sea level and in the shoreline will not be much more conspicuous than they have been for the past century. Most of the great ponds along the south shore presently have surface elevations as high as three to five feet above sea level. With proper management their shorelines, except along the south, could remain relatively unchanged.

Rapid Rise Scenario

In the early 1980s I sat in a conference room at the Woods Hole Oceanographic Institution among many distinguished marine geologists. Dr. K. O. Emery, one of the most conservative of them and a giant in his field, stated that he believed it was possible that sea level could rise by up to 20 feet by the year 2000. While numerous activists lacking credentials have made spectacular predictions, this was coming from one of the great marine geologists of our time, a member of the National Academy of Science, and could not be regarded lightly.

Such an abrupt 20-foot rise in sea level, one foot per year, would probably decimate much of the world economy, drowning many of the major port cities and coastal lands where a large percentage of civilization currently lives. Worldwide social and economic recovery from such an event would probably take many decades, if not a century, assuming the higher sea level remained stable.

The fact that this prediction has not come about does not mean such a change cannot or will not occur. Rather it emphasizes that we did not (and do not) understand the issue sufficiently to make accurate predictions.

If the West Antarctic ice sheet were to melt, as it may have during the last interglacial period 125,000 years ago, sea level could rise from 16 to 23 feet. A rise of 20 feet would have a strong effect on Martha's Vineyard, especially if the rise were rapid. Flooding alone would bring the shoreline about a mile northward on the south shore. Aquinnah, Squibnocket Ridge and Nashaquitsa would become separate islands.

Much of Edgartown town center would be underwater (a benchmark at the corner of Cook street and Katama Road is marked 17 feet). Chappaquiddick Island would be reduced to about half its present size. A barrier beach may form across the harbor near the present location of Long Point. All of Katama Bay would be lost. Cape Pogue proper would be drowned, but there is some chance a new north-south barrier spit would form inland from the present one. Cape Pogue Bay would probably become an open road.

An embayment would form over Sengekontacket Pond, probably without a barrier beach. The high portion of Oak Bluffs, about half the village, would survive. Lagoon Pond with its steep and high walls would retain its current shape, although probably without a barrier beach, and become an excellent harbor. Similarly, Vineyard Haven would escape relatively intact except for the harbor facilities which would need to be rebuilt. Perhaps the ferry dock could be replaced with a floating one to follow the rise of the sea.

The Vineyard Sound coast of Martha's Vineyard is high and steep. It would remain comparatively unchanged. James Cove would become an excellent small harbor. Across the sound, the Elizabeth islands would remain relatively unscathed.

The national economic disaster such a rise in sea level would bring about would no doubt devastate the Vineyard economy. It seems likely the Vineyard would return to a subsistence economy for at least several decades. Property boundaries would become meaningless, as available lands were put into mandatory farming and livestock use. Many summer properties would probably be abandoned by the owners. The fishing industry would probably experience a rebound locally and provide essential food for Islanders.

The Truth

The idea the earth is changing is difficult for many people to accept. The history of geology has been a history of resistance to startling new ideas that point to a dynamic earth: crustal flexibility (isostasy), ice caps (glaciation), continental drift (seafloor spreading), change in the gaseous composition of the atmosphere and variations in sea level are examples. Changing shorelines are even more conspicuous and rapid instabilities that threaten our sense of security.

The truth of what is happening and has happened on the planet earth is more astonishing, more exhilarating, and more humbling than the best science fiction can concoct. Perhaps most significant is that change is inevitable. Many of these truths have consequences we can observe on Martha's Vineyard.

Arthur G, Gaines Jr. is an expert on Vineyard waters and a respected marine scientist at the Woods Hole Oceanographic Institution.