Exposed clay beds at low tide.

Photo: Will Husby

Shores

The Curious Clay Beds of Kwilákm

On this Page

Discover Kwilakm » Story » Shores » The Curious Clay Beds of Kwilákm
Clay beds
Much of the flat shore area seaward of the Causeway is the eroded top of the clay bed that underlies the area from Deep Bay neighbourhood to Snug Cove. Thin layers of beach sand and offshore sand cover parts of the clay surface. Photo: Bob Turner

Kwilákm has an unusual geology. A thick bed of clay, found only in a few other places on Bowen Island and around Howe Sound, underlies the Kwilákm and Snug Cove area. The clay bed has had a profound influence on the shape of the bay and European settlement of Bowen Island.

Clay is geological material made up of very fine mineral grains. This clay bed was formed on an ancient seafloor during the Ice Age from glacial flour carried to the sea by glacial meltwaters. The soft clay banks have been easily eroded by storm waves, causing retreat of clay banks and creating the broad tidal flats of Kwilákm near the Causeway. The gently sloping surface of the clay bed made it an ideal site for the Union Steamship Hotel, Snug Cove village, and later on, the Kwilákm and Snug Point neighbourhoods.

The clay bed was even mined for brick making in the 1800s (see the Deep Bay Brickyards story), fuelling Bowen’s early economy.

A cut away view of the underground near the Causeway from the Deep Bay neighbourhood (north) to Snug Point (south). The clay layer underlies beach deposits along the shore, and overlies bedrock. Retreat of the two clay banks has created the broad clay flats. Figure: Bob Turner/Will Husby
This map shows that the clay bed forms the foundation of the Deep Bay neighbourhood, the Lagoon area, and downtown Snug Cove. Figure: Bob Turner/Will Husby

Clay Beds Map

Click below to highlight each area on the map.

Bedrock
Clay
Clay Flats

The clay bed contains scattered pebbles and boulders, and so along the intertidal shoreline of Kwilákm where the clay is exposed, these stones litter the clay surface. As the ocean waves have eroded the soft clay, these hard stones are left behind. These stones cover the surface so completely in places that they disguise the clay bed beneath. Whenever you see cobbles and boulders in the intertidal zone near the Causeway, you can guess that they are likely eroded from the clay bed.

The strange Ice Age origin of the Clay Bed

The clay bed formed near the end of the Ice Age when sea level was 150 m higher than it is today and the lower elevations of Bowen Island and all of the Vancouver region were seafloor. At that time (13,000 years ago) Ice Age glaciers were melting back up Howe Sound, releasing a great flow of melt waters into the Sound, and icebergs were breaking apart from the glacier front. The melt waters carried huge volumes of glacial flour, rock ground to fine silt by the eroding action of the moving glacier. This glacial flour mud settled out on the sea floor of Howe Sound, creating a thick layer of mud. Pebbles and boulders eroded and carried by the glacier became a part of icebergs that broke free from the glacier front and floated down Howe Sound. As the icebergs melted, these pebbles, and boulders were released, falling down into the muddy seafloor, forming a mix of mud, pebble, and boulder. If you take a close look at the clay bed, you can see all three of these components.

Kwilákm then and now: a) 13,000 years ago sea level was 150m higher and the Deep Bay area was seafloor that was accumulating mud, pebbles, and boulders from the retreating snout of a floating glacier; b) today the Ice Age clay layer forms the land of our Bowen Island neighbourhoods, and our shorelines. Figures: Bob Turner/Will Husby
When the ancient sea level fell to its present position about 5,000 years ago, the clay bed formed part of Bowen’s eastern shoreline. Ancient Terminal Creek flowed across the clay bed to the ocean, cutting a ravine in the clay. At the shore, the banks of the ravine were exposed to wave attack, causing erosion and retreat of the soft clay. Over time, retreat of the clay banks due to wave erosion left behind a gently sloping eroded floor of clay, referred to as the clay flats. Figures: Bob Turner/Will Husby.
Clay bed exposed in bank
Secrets of the clay bank! If you peek under the overhanging vegetation on the shoreline clay bank near Mother’s Beach you can see the clay bed with a matrix of clay (ancient seafloor mud) that contains boulders dropped to the ancient seafloor from floating icebergs. Photo: Bob Turner
Rock clay hoodo
The clay bed is viewed during a low tide along the northern shore of inner Mannion/Deep Bay east of Mother’s Beach. Here the clay bed (olive grey, foreground) is well exposed by the erosion of winter waves. A rock boulder (right) which has eroded out of the clay bed while protecting the clay below it, forms a ‘hoodoo’ feature. Oysters (left) are also abundant on the clay layer. Photo: Bob Turner
Honeycomb in clay bed
The clay in the clay bed is very compact and some clams and other organisms bore holes in clay, creating a honeycomb textures. Photo: Bob Turner
A large rock covered in oysters, mussels, and barnacles resting on sea bed at low tide.
A boulder eroded from the clay bed rests on top of the brown clay bed. The boulder surface is host to oysters and barnacles. Some oysters below the boulder are attached directly to the clay. Photo: Len Gilday