What Is a Beach?

If you’re like most folks, you likely don’t think about sand beyond its presence beneath your towel while sunbathing or as a nuisance clinging to your skin after a good beach day. To some, though, sand is consequential — I’ve spent the better part of four years studying sand; wars are fought over sand (a key component in concrete). Whether or not you have big opinions about sand, the origins of Martha’s Vineyard’s beach sediments might surprise you!

What is a Beach?

By region, the answer is likely to be variable. Most of us probably envision a curve of white sand, turquoise tropical water, some palm trees; around here, we might think of the gentle waves at State Beach, the glory of the Aquinnah Cliffs, or perhaps the memory of Lucy Vincent’s sentinel looking out over the ocean. 

Along the eastern seaboard, our coast is varied. Maine is known for its rocky shores, where fingers of bedrock hold stalwart against the relentless tides, and beachgoers are treated to the rhythmic clatter of well-rounded stones against bedrock that might be half a billion years old. At the opposite end of the eastern coast, Florida’s quintessential beaches are made up of quartz sands and coral fragments and are popular amongst beachcombers for the variety of shells to be found along endless shoreline. 

Of course, beaches are one of the Vineyard’s many draws, each with its own character and story. But why are they here? How did they form? And why do they seem to change so much year to year?

As a kid, I knew that some of our beaches were made of really old stuff, because when I walked along the south shore after a big storm, I would find fossilized shark teeth. I always wondered how old those teeth actually were, and why they only appeared on certain beaches. Most vexing of all was: how did the Aquinnah cliffs come to be? Now, I am a geoscientist, and I have begun to dig into some of these lifelong questions. 

If you’ve had similar questions or found a cool rock on Martha’s Vineyard and wondered where it might’ve come from, I hope to provide some fodder for thought. I’ll warn you though, writing this has taken me far longer than I’d like to admit, because there is so much depth to each of the questions I posed above. I’ve noodled through Charles Lyell’s 1845 book, Travels in North America (See here), and Henry Fowler’s 1911 A Description of the Fossil Fish Remains (I’d hoped to make a quick identification guide to shark teeth found on the Island, but that’s a project for another time), as well as plenty of more recent publications. Should you share my interest, there is no shortage of material to dig into. For now, we’ll start with the basics.

How Did Our Beaches – and Our Island – Come Into Being?

Geologically, the Vineyard is somewhat unique and quite young. Along with Nantucket and Long Island, Martha’s Vineyard is part of the southernmost extent (what we call the “terminal moraine”) of the most recent ice sheet that extended from the arctic across North America. This ice sheet, known as the Laurentide Ice Sheet, scraped the tops of mountains, wrenching up rocks and scouring valleys, as it moved generally south across New England. More than a mile thick in places, the ice eroded and conveyed material from Canada southward, bringing boulders, gravel, and sand, over, under, and through the ice as it advanced southward. During the peak of this glacial period, much of the world’s water was trapped in ice sheets, resulting in sea levels 400 feet lower than what we are used to today. 

The ice sheet reached what is now the islands some 27,000 to 25,000 years ago, at which point the rocks and sand that we walk on each day began to accumulate as the glacier flowed like a river in slow motion. As I learned from Chris Halsted, author of a recent publication that estimates the rate of ice retreat of the Laurentide ice sheet, the material that makes up Martha’s Vineyard was delivered, distributed, and uplifted over the course of only a few thousand years. 

Within that “brief” time, several processes occurred simultaneously to form Martha’s Vineyard. As mentioned above, the glacier conveyed sediment over untold miles, including giant boulders like that of Great Rock Bight, Waskosim’s Rock, and the Plymouth Rock, as well as unimaginable amounts of gravel, pebbles, sand, and clay. This material accumulated at the edge of the ice sheet, forming moraines. While much of the moraine material remains today as the higher elevation areas (think Menemsha Hills or Cedar Tree Neck), seasonal meltwater floods from the ice sheet redistributed these sediments intermittently as well. Similar to the way in which ocean waves deposit cobbles, pebbles, and sand, these floods deposited heavier materials first — dropping first rocks, then gravel, then finer sands as the water and energy propelling the floodwaters dispersed. The result of this intermittent flooding was the formation of the flatter central and southern part of the Island. The ponds along the south shore of the Island were scoured. 

Current research comparing a handful of geologic dating techniques suggests that the ice sheet began to recede northward from its terminal location (here) between 24,000 to 20,000 years ago. On human timescales, a few thousand years of glaciation outlasts  most civilizations, but on geologic ones, it’s a mere blip.

As the climate changed and ice sheets around the world shrank, the water that had been stored on land in these massive frozen reservoirs was gradually released back into the oceans. The landscape 20,000 years ago here would have been unrecognizable. Standing at Long Point Beach looking south, you would have seen a seemingly endless expanse of sand and gravel, crisscrossed with braided streams and completely devoid of vegetation — no ocean in sight. Looking north, you’d have observed the undulating texture of the frost bottoms, providing direction to the upstream segments of the rivers shallowly cutting through a gently sloping wedge of sediment. Beyond that, you’d have found a massive, continuous mound of boulders and smaller rocks — the terminal moraine and the northern edge of the island we now know. Beyond the moraine was the source of sediment and flowing water — the toe of the ice sheet itself, looming some 1,500 feet above the ground, and beginning its northward retreat at a rate of about 50 meters per year, according to Halsted.

How Did the Aquinnah Cliffs Form?

The material that makes up the Aquinnah cliffs was deposited here far before the Laurentide Ice Sheet came to town. These sediments — primarily clays in striking red, white, and black — were initially deposited at the bottom of a calm sea roughly 90 million years ago, during the cretaceous period (think roaming dinosaurs and the breaking up of supercontinent Pangea). A few tens of millions of years later, the greensand (basically, sand or sandstone that is greenish in color due to the minerological composition) bearing sharkteeth (beautiful story in MV Magazine about that here) was deposited on top. When the Laurentide Ice Sheet found her furthest extent, she was resting heavily atop these layers of Earth history. The pressure of the heavy ice and its southward flow began to reshape these layers. 

Humor me for a moment and think of these layers as an unbaked lasagna in a pan. Let's say the ice sheet is a one-pound block of cheddar cheese. If you were to set the block of cheese on top of half the lasagna, what might happen? 

With the added weight, the red sauce and ricotta mixture might start to migrate to the unburdened side of the pan. The more consolidated layers (your noodles) might become compressed on the cheddar side, and start to form a bulge on the no-cheddar side. In time, the cheddar will have weighed down one half of the lasagna, and most of the ingredients will have been squeezed toward the other side of the pan, becoming intermingled and forming layers of varying thickness. While massively oversimplified, this is an apt description about the way that the Aquinnah Cliffs came to be. The pressure from the ice sheet uplifted and deformed the underlying clay layers, gradually creating a massive bulge of swirling dinosaur-aged clays and Megladon-teeth-bearing-greensands beyond the toe of the ice sheet. 

For their origins, the plant and animal fossils they hold, and their cultural significance, the Aquinnah Cliffs are perhaps the most fascinating part of the Island. While I can’t speak about the cultural context of the cliffs for the Aquinnah Wampanoag tribe, I have found great information in both Helen Manning’s book, Moshup’s Footsteps, and the Wampanoag Tribe of Gay Head (Aquinnah)’s website, which I highly recommend. Through these resources, one can learn that the Island was formed by a being known as Moshup, who was quite large in stature, and made his home in the Aquinnah Cliffs. Moshup regularly caught whales to feed himself, his family, and his people, and the blood of the whales is said to have stained the Aquinnah Cliffs deep red. The Aquinnah Cliffs are and have been many things in the time since Moshup made his home here, including a source of raw materials for ceramics, a gathering place, a refuge, and a location of widely appreciated natural beauty, stewarded for at least ten thousand years by the Aquinnah Wampanoag peoples. 

While one may naturally assume that the Wampanoag People initially reached the Island via watercraft, there was in fact no ocean between Cape Cod and Martha’s Vineyard on which to float their vessels at that time. Instead, the people of 12,000 years ago are known to have walked between what’s now the mainland and the Island, seeking access to seasonal hunting grounds. How different this landscape — and the species just beginning to take hold in this newly exposed terrain — must have been. Through generations, those early Islanders’ descendents observed the sea level rising, bringing the ocean slowly closer. They saw the climate change, and with it the ecosystems within which they lived. The pioneering post-glacial boreal forest was replaced with conifers, and then deciduous trees; mammoths and their ice-aged brethren were no longer suited for this environment, and the animals of today gradually found their way here. About 7,500 years ago, the Vineyard Sound held seawater for the first time in its new form. So began the rhythmic oceanic reshaping of these new landforms, whose prominence was annually diminished as the ice sheet, now confined to the arctic, continued to give water back to the tides.

When finally the ocean met the perimeter of our beloved heap of sediment a mere 2,000 or so years ago, the process of Martha’s Vineyard’s erosion began in earnest. 

Erosion is a constant concern in any coastal community, and perhaps especially on an island. As local soil scientist Doug Cooper reminded me (see the story he did a few years ago here), the only constant is change. As the ocean currents daily visit our shores, they push and pull sediment with them, sometimes taking, sometimes depositing. A study comparing the Martha’s Vineyard coastline over almost 200 years by Clifford Kaye (published in 1973) found that while much of the Vineyard’s coast is being eroded, the Island was then growing in select locations too. One important thing to note is the predominant direction of sediment transport (“longshore drift”), which can help explain why, for example, Dogfish Bar is gaining shoreline while the adjacent Aquinnah Cliffs are being eroded. Beaches share their sediment down current — when there aren’t pesky jetties in the way, that is. 

Much has changed in the more than 50 years since Kaye’s study, including sea levels, which NASA suggests have risen about six to eight inches in the past century. With all of these processes constantly in motion, it is remarkable that our island of sediment generally holds steady and changes relatively little day after day, amidst these endless waves.

Back To the Beaches

Have you ever wondered why sometimes a stretch of up-Island beach is rocky, while other times it's sandy? Day after day, incoming tides transport sand and debris onto the beaches, and outgoing tides drag these materials away. Rougher seas can carry larger pebbles and rocks, and tend to take sand back out with them — think about a typical day at Squibnocket — whereas calmer seas will deposit finer grains of sand like what you typically find at Lambert’s Cove. Seasonally, winter storms tend to erode beaches, creating offshore sandbars like those you might find along the south shore. In the summer, sand from these bars often gets transported back to shore. Meanwhile, all of this back and forth makes beach rocks smaller and rounder, eventually forming new sand. 

Unless you are at a volcanic beach, most beach sand is composed of the mineral quartz. I’ve spent the past four years thinking about quartz, collecting it from tropical streams, transporting hundreds of pounds of it across oceans the unnatural way (via airplane), all to ultimately dissolve it in acid in the pursuit of the radioactive form of beryllium (a tool for measuring erosion and burial, and a tale for another time). Quartz is both super robust and super common. Unlike diamonds, which are prized for their manufactured rarity, quartz should be celebrated for its accessibility. Quartz is pure silica and oxygen, but when just a few impurities are added in (an imperceptible sprinkle of other atoms), it goes by other names — amethyst, citrine, and rose quartz, for example. While other minerals like pyrite (fool’s gold) may catch your eye, most are not nearly as durable as quartz, and break down at the temperature and pressure conditions found at Earth’s surface. (Having come into being at hundreds of degrees celsius, with miles of Earth’s crust acting as a very heavy weighted blanket, they find conditions on the surface way too cold and low-pressure). 

While beaches like Squibnocket offer rounded cobbles and pebbles that were once part of bedrock formations from here to Canada, calmer beaches offer the sand-sized fragments of their brethren, slowly broken down from a mass of minerals into single individual grains. Each mineral has specific characteristics that determine its longevity and resistance to weathering. Micas, for example, which are recognizable by their shiny, platey characteristics, fall apart rather quickly when exposed to the elements, especially when water makes its way between the mineral’s thin layers and exploits the weaker atomic bonds there. The thin sheets are then easily broken into tiny, clay sized particles, which remain suspended in water, and end up being deposited far from shore, where the waters are far calmer and allow the tiny particles to settle to the seafloor. By comparison, our champion quartz is tough and stalwart, outlasting most other minerals through the weathering process and becoming the king of the beach simply by longevity. 

In Our Lifetimes

Perhaps, like me, you mourned the somewhat recent loss of the sentinel cliff at Lucy Vincent beach. My career trajectory may have begun with the childhood question, “why are the Lucy Vincent cliffs eroding so fast?” I could not understand why the cliffs were a little different every time I visited them. I’m still shocked now, despite growing up alongside the Keeling Curve (the graph that plots the increase in concentrate of CO2 in the Earth’s atmosphere), rising sea levels, and more intense storm systems resulting from our changing climate — all major contributors to the loss of coastal areas. 

Watching parts of the Island slowly fade into the ocean has been a perturbing aspect of growing up. As the Greenland and Antarctic ice sheets annually lose more mass than they gain, and the tides endlessly lap at our coastline, we will continue to see such changes. Perhaps (forgetting for an instant the infrastructural implications) we can also recognize this as a unique opportunity to watch our young Island mature and change with her surroundings.

In the end, if you’re here for the beaches, do enjoy the unbeatable trifecta of sun, salt, and glacially-delivered sand, and while you’re doing so, maybe consider the ways in which you can contribute to their longevity. Do your elected representatives know you care about climate change? While personal lifestyle changes are important, driving leadership and industry to strive for efficiency and sustainability can make a significantly larger impact. To any modern captain of industry touched by this special place, now is the time to do your part to steward our one perfect planet for generations to come. 

What You Can Do

Important! First, don’t climb on the cliffs or dunes at Aquinnah, or remove anything from the cliffs! These are extremely fragile parts of our coastline that are more swiftly lost when battered by both humans and the sea. The Aquinnah Wampanoag tribe shares this beautiful place with all who wish to visit, and has created rules to preserve it for future generations. The least we can do is support this mission by staying on trails and leaving the cliffs to their natural processes. 

I wholeheartedly recommend checking out David Foster’s A Meeting of Land and Sea: Nature and the Future of Martha’s Vineyard (available in local bookstores and on Amazon). There you’ll find answers to questions you didn’t know you had. Similar articles with different foci by Christine Schultz and Alex Elvin may also be of interest.

To learn about the Wampanoag origin stories of this land, Helen Manning’s Moshup’s Footsteps is an excellent starting place, as would be the Aquinnah Cultural Center and their newly opened ACC Wampanoag History Museum.

A more contemporary personal experience can be found in Joseph Vanderhoop Lee’s book, Nothing More of This Land: Community, Power, and The Search for Indigenous Identity. An interview with the author can be found here.