Tuesday, 4 September 2012

The Kitsilano Natural Foreshore

Between Jericho Beach on the west, and Trafalgar Street on the east, lies the only section of undeveloped beach within the city of Vancouver. Contrary to what some people believe, this whole stretch of foreshore is public land, and is relatively easily reached from a number of access points. These points are located at Jericho Beach, Dunbar Street, Waterloo Street, Balaclava Street, Bayswater Street, Volunteer Park, and Trafalgar Street.

Other shoreline areas in the city such as Stanley Park, English Bay, Kitsilano Beach and False Creek are also public land, but all of them differ significantly from a natural foreshore. They are dedicated to active recreation, and the natural environment has been significantly altered. Between Jericho and Trafalgar, although the land has been converted to residential properties, the beach itself remains little altered from what it would have been like several centuries ago. There are many features and organisms here to entice the curious naturalist. It also remains an area for passive recreation, an oasis different from the frenetic pace of the other beaches. Such places are now difficult to find within the city.

There is, however, pressure to change this situation. A proposal has been made to build a seawall along the beach. Such development would seriously impact this last remaining piece of natural foreshore habitat. Contrary to some claims there are natural features here worthy of preservation.

In this article, we will take a walk along the beach from west to east, and look at these features. Before starting, however, there are a few safety precautions. This is a natural beach. For most of its length it lies at the base of a cliff. At high tide the sea comes up to the cliff. Before you take your walk check the tide tables on the Internet to make sure you can safely proceed. Also take note of the access stairs which are located approximately every two blocks. These will take you up to Point Grey Road, so you can explore the whole beach or just a portion of it. Where there is no sand the rocks are covered by a biofilm of diatoms. We will get back to the importance of diatoms later. Of immediate concern is the fact that this biofilm is very slippery and you can take a bad fall. So be careful walking across it.

The information here is gleaned from both my own knowledge of the beach, that I have acquired over the years, and also from other members of Nature Vancouver with whom I have visited the foreshore recently.

So let us begin with an overview of what is here. When the tide is out and you look to the north, you see a flat area stretching out to the water’s edge. Geologists call it a wave cut platform. The present site of Vancouver was below sea level during glacial periods, being pushed down by an ice sheet several kilometres thick. When the ice retreated, 11,000 years ago the land rebounded, and the cliffs which now lie at the back of the beach were out at the edge of the platform. The action of millennia of storms have cut away at them and left the platform which is now exposed at low tide. At the base of the cliffs you can see an undercut zone, where the sea is cutting into the present cliff. 

Although the platform is flat, you will notice that some of the rock strata on it, especially close to the beach are inclined. They are steep on the north side, and slope gently on the south side. The sea has not yet had time to completely level them. They are tilted because of the North Shore Mountains. The sediments were originally laid down flat, but that was long before the North Shore peaks existed. The original hills were worn away and their components deposited in places like this. Continental drift is pushing the Pacific Plate against North America, and part of this process has produced the local mountains. As the peaks have risen the rocks here at the beach have been tilted, so that they slope slightly to the south.

The tilted platform
Photo by Terry Taylor

Along the platform is the biofilm of diatoms. This is the brownish slippery coating over the sediment and rock surface. At a lower level than the sandy beach there is a coating of clay and silt. This has been deposited both as silt brought from the Interior and the Rockies by the Fraser River, and by the action of the sea upon shale within the cliffs. The upper beach is sand because the scour of the tides is stronger here and removes the finer materials. It is upon the silt and exposed rock platform where the diatoms and other micro-organisms can find a safe haven, and can establish themselves. Diatoms are single celled algae, or short chains of such cells. They are distantly related to brown seaweeds. Under the microscope they are very beautiful, and are reminiscent of bivalve mollusks. They cover themselves with two shells, but these shells are not calcium carbonate. They are made of silica, and are transparent, like two halves of a petri dish. Diatoms may not seem very important, but they, and other micro-organisms, are the beginning of the food chain. They feed juvenile fish, or the crustacea that are eaten by larger fish. Although, we are usually aware of the big organisms only, biologists have estimated that half the weight of the biosphere is composed of the microscopic ones.

Also very noticeable along the edges of the beach are rafts of seaweeds. The tides have torn them from the rocks and brought them ashore. As they decay they are eaten by crustaceans. The ones that jump about are often called sand fleas, although they have little in common with fleas, except that they are very good jumpers. They do not bite. If you lift up some seaweed you may see hundreds of them. They are food for the smaller fish, which in turn feed the larger fish such as salmon. There are two main species of seaweeds here. Most common is the rockweed (Fucus gardneri). This is the brown one which covers intertidal rocks. It has the floats which dry out and go pop when you walk on them. The other is sea lettuce (Ulva lactuca). These are the green sheets that look like thin lettuce. It is a green alga, related to the ancestors of land plants.

The beach too, has a tale to tell. Many of the pebbles here have been brought down by the Pleistocene ice sheet from the North Shore Mountains and beyond. They were dumped in the ocean by the advancing glaciers. The Point Grey Peninsula rose above sea level after the ice left, as the glacier was no longer pushing it below sea level. The sea cut away at the cliffs over the centuries, and the pebbles ended up on the beach. The smaller pebbles are also significant for another reason. During the summer, when the tide is in, smelt lay their eggs on them. The eggs hatch in a couple of weeks and the larval fish swim out to sea, feeding on micro-organisms as they migrate. Smelt are now a threatened species. They need all the help they can get to re-build their population levels. Overhanging shrubs and trees along the upper beach are also important for smelt spawning, as their shade cools the beach when the tide is out. These spawning gravels along the beach may be protected by fisheries legislation. During August, when I was in elementary school, and the tide was full in the evening, I often came to the beach with my smelting net.

Take a look at the cliffs when you have a chance and you will see that they are composed of two different types of rocks - sandstone and shale. These deposits are remnants of the ancient history of the British Columbia coast. They originated 40 million years ago, during the Eocene Epoch, and were laid down as sediments along the channels of rivers that have long ceased to exist. These rivers flowed westwards from a range of low mountains that fronted the coast millions of years before our North Shore mountains were uplifted. The sandstone was formed where the currents were flowing strongly, and the shales from fine clay in gently moving backwaters. If you go down to the Fraser delta and look at the estuarine plants along the edge you will see evidence of a similar process. These plants are covered by a gray coating. This is fine silt carried by the river from the interior of the province. 

In some spots there are sandstone layers that actually show how the river was flowing, possibly on individual days, so many millions of years ago. Within the layers of sand are occasional thin black deposits of organic material. These stand out from the lighter colored sand layers. You will see that some of them are tilted slightly from others, indicating how the currents were changing their course.

As we walk eastward from Jericho we will stop at various features of interest. The first of these is along the sand near the Royal Vancouver Yacht Club. At this site you will see what a natural, undisturbed deep sand beach looks like. There are two robust grassy plants here. On the right, shoreward side is the dune grass (Leymus mollis). This is a very large grass that can grow up to two metres tall. Notice how thick and tough the wide blades are. This is an adaptation to the harsh conditions posed by growing in sand. These blades resist the abrasion of wind blown sand and also retard water loss. Upper layers of sand can be very dry, plus the fact that the water which does occur at lower levels is often salty, and not easily absorbed by plants. The dune grass also has a gray coating to retard water loss. It has deep roots which penetrate down to the water table, and stabilize the plant in this shifting unstable environment.

To the left, the seaward direction is a plant with shiny grass-like leaves. This is a grass relative, but not actually a grass. It is a sedge, the big-headed sedge (Carex macrocephala). The leaves are smaller than the dune grass and are a bright green color. It grows close to the sand in little tufts. These tufts are sometimes in straight lines as they are often not single plants but shoots attached at intervals along long, horizontal, underground stems. The most noticeable feature of big-headed sedge are the compact clusters of dark brown seed heads. The seeds themselves are contained within seed cases that possess two sharp points. This sedge is now reported as a rare plant in Washington State.

The next point of interest is just down the beach, where the sandstone cliff begins. Projecting from the cliff as well as upon the beach are large rounded sandstone boulders. This is the only site along the entire foreshore where these strange boulders are found. They are called concretions, and they consist of sandstone which has been cemented together by calcium carbonate, deposited within them by water. They stand out because they are harder than the surrounding rock, and are, therefore, more resistant to weathering. How this lime material was deposited, why it is here and not in other parts of the cliffs, and how old it is, are all unknown. One of the geological mysteries of the Kitsilano foreshore, and one which is worthy of protection. 

One of the mysterious concretions at Jericho Beach
Photo by Terry Taylor

The next feature is just east of the Dunbar Street access steps. It is right at the base of the cliff, where the force of the waves is cutting into the rock. It is at the cliff base where the energy of storms is at its greatest. Basically what they are doing is gradually extending the wave cut platform landwards. At this particular undercut there is a layer of shale with black coatings on it. If you look closely you will see the impressions of leaves. These are fossils of leaves from deciduous trees which once grew along the river banks 40 million years ago. When you look at one of these leaves you are looking at something that happened one autumn of one year, so many eons ago. These were deciduous trees. They shed their leaves during the fall the same as our trees do. The leaves fell into the river, were carried down stream until they became waterlogged, fell to the riverbed and were covered by silt which accumulated above them for century after century, metre upon metre.

One of the fossils from the cliff near Dunbar Street
Photo by Rosemary Taylor

About a block east of the Waterloo Street stairs is a strange looking rock formation projecting northwards from the shore. Most people just see it as an impediment that must be climbed over and makes them wait until the tide is low enough for them to proceed. This, however, is another structure worthy of protection. Notice that the central part of it is darker and harder rock that that on either side. It is a volcanic dyke. It is the only one along the entire beach. A similar dyke in Stanley Park has been dated at 32 million years, so this is likely to be of a comparable age. The dark central part is basalt or a related volcanic rock and it was pushed upwards from a magma chamber below it. These structures are the roots of volcanoes or lava flows. So, 30 million years ago there may have been a Kitsilano volcano, or a lava flow like the Columbia Plateau. Note that sandstone occurs on either side of the dyke. When the lava erupted it roasted the sandstone through which it was extruded. The sediments on either side are, therefore, harder and more resistant to erosion than the surrounding rock and we now have this long three layered stone sandwich. 

When you reach Bayswater Street, if it is a low tide, look out along the exposed flats. You will see there is a smooth area without rocks. This is a piece of local history. Over a century ago the rocks were cleared away and the English Bay Cannery was built here. Although this salmon cannery is long gone, the smooth surface bears witness to its existence. 

As Trafalgar Street is approached, look carefully at the cliff face. At one spot there are a couple of coal exposures. Again, these are the remains of the ancient trees that once grew here. 

The above features are some of the highlights along the Kitsilano foreshore. They contribute to making this beach unique within the city of Vancouver. Construction of a seawall would destroy this uniqueness and eliminate the last un-impacted beach within the city.