Coastlines of Atlantic Canada
Where Land Meets Sea
Coastlines mark the present boundary of the ancient struggle between land and sea. The eternal crashing of waves on beaches or against cliffs is a reminder of the erosional power of water. But this power is not always destructive. True, some coastlines are being worn away and some are being inundated by the sea because they are sinking relative to sea level. But others are growing through deposition of sediments and the relative lowering of sea level.
How and why do coastlines change? The two main factors are the action of the sea and the type of rock that forms the land. The power of the sea is reflected in tides, waves and currents.
Tidal rise and fall is due to the gravitational pull of the moon. When the moon is directly overhead, there are high tides on the near and opposite sides of the Earth and low tides midway between. This is why there are roughly two tides each day. The intensity of the tides varies according to the phases of the moon. The highest tides occur when the moon is new and full and lower tides occur between these phases. Tides are also affected by the shape of the coastline, and tend to be intensified where there is a funnel effect, as in the Bay of Fundy. In the Bay, the difference between low and high tides varies from 3 metres at the mouth to about 16 metres at Burntcoat Head, the greatest tidal range on Earth. Tidal fluctuations play an important role in molding the coastlines of the Maritime Provinces.
Waves are also critical in the development of coastlines. They are generated by wind on the water surface, and their intensity varies according to stormy or calm weather.
Waves vary in direction and power according to the direction and strength of the wind. As a wave approaches the shore, its lower part hits the beach first and is slowed by friction, but its upper part is driven forward by its own inertia as a breaker. When the breaker collapses under its own weight it sends a mass of water (called the "swash") up the beach. The returning water is called the "backwash". The swash drives the pebbles and sand shorewards, the backwash carries them out to sea. When the swash is the stronger, the wave is constructive and helps to add material the shoreline. If constructive waves are at an angle to the shoreline, the beach material is moved in the general direction towards which the wind is blowing.
In this way, "longshore drift" occurs, and spits and barrier beaches form, as along the eastern shore of New Brunswick. A destructive wave is one with a stronger backwash, which erodes the beach. During storms, the power of both swash and backwash are much greater than usual and the rates of deposition and erosion are magnified. Thus, major storms such as hurricanes have catastrophic effects, causing rapid and dramatic changes to the coastline.
Cliffs and Headlands
Although varied, Maritimes coastlines can be grouped into just a few types, reflecting the nature of the rock or sediment that is being weathered or from the deposited.
Perhaps the most spectacular coastlines can be seen where resistant rocks face the onslaught of the sea and form cliffs and headlands that serve as landmarks along our shore. Such resistant material includes the volcanic rocks along the Bay of Fundy, for example at Cape Split and Cape d'Or in Nova Scotia and in Fundy National Park in New Brunswick.
The soaring granite headland at Cape Chignecto, NS, is another example. It is a paradox that not all hard rocks exposed at the coast form high cliffs. For example, at Peggys Cove, NS, the low rounded scenery formed on granite is a legacy of the erosional power of glacial ice, reminding us that more than just hardness of the rock affects the shape of the coastline.
Low cliffs are common where the rocks are the more easily eroded, such as the Carboniferous sandstones and shales at Tabusintac and
Richibucto Cape in northern New Brunswick and at Sydney Mines, Point Aconi and Victoria Mines in Cape Breton Island. Perhaps the best known example of this type of low cliff, in this case eroded from soft Carboniferous conglomerate, is the Hopewell Rocks, near Hillsborough, NB. Around Sydney, NS, and along the Gulf of St. Lawrence and Chaleur Bay coasts of New Brunswick, the subdued coastal cliffs are so easily undercut by wave and tidal action that slumping and collapse are common. Equally vulnerable are the red sandstone cliffs of Prince Edward Island where, along the north shore, the sea is rapidly encroaching landward. This is dramatically seen at Elephant Rock, where the famous "elephant " recently lost its trunk.
Since glacial deposits are widespread in the Maritime Provinces, they form many low coastal bluffs and headlands. Cliffs of glacial till and outwash are found, for example, along the Eastern Shore of Nova Scotia, in southeastern Cape Breton Island, and at Waterside, near Alma, and Red Head, near Saint John on the Fundy coast of New Brunswick. Perhaps the most unusual coastal feature in the Maritimes is at Point Escuminac, NB, where cliffs of postglacial peat rise several metres above the beach.
Beaches are magical places, whether they are made from mud, sand, gravel, pebbles or a mixture of sediments. Whereas cliffs are symbols of coastal erosion, beaches are indicators of coastal deposition. One of the most common beach types in the Maritimes involves a sand and gravel mixture, formed when glacial till is eroded. Along the Eastern Shore of Nova Scotia, bluffs of glacial till are being destroyed at the rate of one to ten metres each year, the eroded material becoming available for building beaches.
In parts of Cape Breton, such as Aspy Bay, eroded glacial deposits have been reborn as sandy beaches and dunes, which protect enclosed lagoons. Unusual triangular barrier beaches, which surround brackish water lagoons,
extend into the waters of the Bras d'Or Lakes. These beaches are formed by storm waves that move parallel to the long lakes, sometimes from one direction, sometimes from the other.
The beautiful wide sandy beaches of Prince Edward Island, northern Nova Scotia, and the Northumberland Strait shore of New Brunswick are formed from the continuing erosion of the underlying late Carboniferous and Permian sandstones. Sandy beaches are also found at the head of the Bay of Fundy, but the most distinctive features there are the vast sandbanks and mudflats cut by tidal channels. Twice daily, these currents rework the huge volume of reddish, muddy water brought in by the tide. A superb example of a mudflat can be seen where the Avon River enters the Minas Basin near Windsor, NS. Here, however, natural processes have been disrupted by the causeway that carries Highway 101 across the estuary.
A narrow ribbon of sand extending from a headland or stepped out from a shoreline is called a barrier beach. Such beaches help to create constructive coastlines, where the land is at least temporarily holding its own, if not winning. The New Brunswick coast between Miscou Island and Cape Tormentine it the longest stretch of barrier coast in Canada, with barrier beaches and spits extending across shallow drowned estuaries. The North and South Kouchibouguac beaches in Kouchibouguac National Park, and the twelve kilometre long Buctouche Dune are good examples.
Every year, gravel and sand are pushed landward by storm waves, causing the beach to migrate inland but stay above sea level. Often the barrier beaches protect brackish and freshwater lagoons, such as in the Cape Sable area of Nova Scotia and along the Atlantic coast of Cape Breton Island. On the northern coast of Prince Edward Island, sand is carried eastwards by offshore currents and is deposited at East Point, where it forms a huge underwater bank. At Basin Head, PEI, and nearby areas, vast amounts of sand have accumulated as successive beaches, which have been "glued" together, forming ridges partly overgrown by forest. Many barrier beaches and spits protect some of the small fishing harbours of our region, as at Advocate Harbour, NS.
In low coastal areas of the Bay of Fundy and elsewhere, sediment carried by the tide can be trapped by salt marsh grasses such as Spartina alterniflora and Spartina patens. In this way, marshes grow upwards as sea level rises. When the Acadians settled the Fundy coastal lowlands, starting in the 1600's, they built dykes to cut off the salt marshes from the sea. Parts of the original Acadian dykes are still visible on the Tantramar Marsh, near Aulac, NB. In the cliff, half a metre below the present marsh surface, are the remnants of a corduroy road, 300 years old according to radiocarbon dating. The system of dykes is still maintained, so that a large part of the marshes is now protected from the rising sea by dykes, providing good pasture. Today, only fifteen percent of the original marsh remains. Agricultural land, roads and houses behind the dykes lie well below the high tide level. Much of the region was flooded by the Saxby Gale of 1869, and would be flooded again if a storm sweeping up the Bay of Fundy should catch the highest tide.
The changing nature and history of the marsh is "written" in the sediments. On the Tantramar Marsh, for example, sediments deposited since the end of the last glacial interval are up to 30 metres thick. Within these, remnants of a 4,000 year old forest, with trunks up to a metre in diameter, are visible at the base of a cliff about two kilometres north of Fort Beausejour, NB. Cedar, hemlock, pine, fir and beech were growing on glacial soil when they were buried by marine sediments brought in by the rapidly rising sea and increasing tidal range. The rise of sea level here (about 30 centimetres per century) has taken place in a number of pulses, reflected in the alternation of silt and clay layers, deposited during rapid sea level rise, and peat layers, formed during slower sea level rise. By unravelling this story, we should find clues as to what may happen when sea level changes in the future, with or without human influence.
The construction of dykes, dams and causeways influences water levels, erosion, sedimentation and peat growth, which in turn affects fish and other wildlife, as well as human activities such as farming. An example of change to the marsh caused by people is found at Windsor, NS, where a causeway was built across the Avon River in the 1960s for Highway 101. This artificial barrier reduced the strength of the tidal currents, so that at least 10 metres of mud has been deposited since then. The mud flats have now built up almost to high tide level and are grassing over. Thus, a new salt marsh is forming.
Bays and Inlets
The convoluted Atlantic coastline of Nova Scotia has numerous bays and inlets, some of which have been deepened by glaciers. Good examples are Bedford Basin and St Margaret's Bay, both in Nova Scotia. Halifax Harbour is a deep, sheltered, bedrock bay. Ten thousand years ago, the Bedford Basin was a freshwater lake with a narrow outlet through Halifax Harbour to the sea. About 6,000 years ago, rising sea level flooded the lake and formed the present harbour.
Other inlets have been partly filled by sediment during the rise of sea level over the last 10,000 years. A typical inlet formed through the action of ice and rising sea level is Chezzetcook Inlet, NS, an estuary surrounded by fields of drumlins. In the outer estuary, the drumlins act as anchor points for gravel barrier beaches that protect the estuary from the Atlantic Ocean.
One of the most dramatic inroads of the sea in this region produced the Bras d'Or Lakes, billed as the largest inland sea in Canada.
The setting of wooded hillsides, tranquil pastures and fine houses such as Alexander Graham Bell's Beinn Bhreagh, give the region a lakeland look.
But the seaweed in the water is a constant reminder that the Bras d'Or Lakes are part of the sea. This wasn't always so, however. Since the last ice age, the lakes have been joined to the Atlantic Ocean, separated and joined again as sea level successively rose and fell. Today, the salt water enters through the narrow inlet north of Sydney and reaches into the heart of Cape Breton Island in a maze of long channels.
Islands conjure up mystery, perhaps none more so than Sable Island, dubbed the graveyard of the Atlantic because of the numerous ships that have been wrecked on its treacherous shore. This far-flung piece of Nova Scotia, on the edge of the Scotian Shelf, is 40 kilometres long and less than 1.5 kilometre wide. It is the remnant of a much larger island that has been gradually submerging over the past 15,000 years. The windswept, storm-battered outpost is composed entirely of sand. Behind the shallow shifting bars and wide sandy beaches are coastal dunes up to 30 metres high, covered with marram grass. Marram thrives where it can trap wind-blown sand, and is replaced by other plants when the supply of sand dwindles. The scouring action of wind and trampling of wild horses maintain the supply of blowing sand, and as dunes erode, new dunes grow nearby, constantly renewing the island.
Several islands in the Bay of Fundy represent isolated sentinels of early Jurassic basalt, survivors where less resistant rocks have been washed away.
The most famous are Brier Island in Nova Scotia and Grand Manan Island off the New Brunswick coast. But there are other islands such as Île Haute, which lies off Cape Chignecto. Campobello Island, the location of Franklin Roosevelts summer cottage, is also situated in the Bay of Fundy, but the sedimentary and volcanic rocks there are much older, dating from the Silurian. Erosion of glacial deposits such as drumlins and till often leads to formation of islands along our coasts. One of the best examples is at Story Head Beach in Chezzetcook Inlet, NS. The beach that links the mainland to an eroding drumlin has migrated landwards at more than 8 metres each year over the last 30 years. In 1998, the beach was completely destroyed by a storm, so that Story Head is now an island. Like other former islands nearby it will eventually disappear beneath the waves, a reminder of the ephemeral nature of our coastline.
One of the most famous islands in eastern Canada is Prince Edward Island. It was formed from the famous red sandstone of Permian age. Smaller islands with similar origins are found in the Northumberland Strait, such as Pictou Island off Nova Scotia.
The coast that we see today is merely a snapshot in time, a pause in the continuing changes in sea level. Eight thousand years ago, the coast was many kilometres seaward. Five thousand years ago, the Northumberland Strait was a long valley draining to the east. And in a few thousand years much of the coast will have migrated inland. One thing we can be sure of is that the eternal battle between land and sea and the constantly changing coastline will be always full of surprises, beauty and inspiration.