Cathedral Cliffs

The rocks comprise layers of soft sandstone and siltstone together with harder gravel deposits. Landforms like form what earth scientists call badlands topography, or in America, are often referred to as hoodoos. In other countries such badlands might occupy vast areas such as in Alberta (Canada), Utah and South Dakota (USA), but here at Gore Bay, they occur in just the small canyon area southwest of the community.

When the rain falls, the gravel layers form a more resistant layer which protects softer sediments below from being washed away. Sometimes all it takes is for a large stone positioned at the top of the pillar, to protect the softer sandstone and siltstone layers below from being eroded. Rainwater hits the gravel layer at the top of the pillar and flows vertically down to the base, and this forms the very marked vertical ribs forming the pillars a bit like cathedral spires. The brown-coloured rocks at Cathedral Gully are about 2 million years old and also occur in the coastal cliffs south of Gore Bay. They have not been eroded into pillars along the beach as younger sediments and soils overlie them in this area, protecting them from erosion.

How long do the pillars last? Individual pillars might last decades; others for only a few years before they a whittled down to a small stubble or fall over. The rate of erosion depends on the intensity and amount of rainfall and the degree of protection offered by the gravel. Once eroded, other pillars however form in their place, and there is ample rock available for the process to continue almost endlessly.

Observe how some layers in the cliffs have eroded more than others - the ones that stick out more are less prone to erosion. Can you see what grain size the less erodable layers are? Are they conglomerate or sandstone? Is it always the same type of rock? Conglomerates typically have big stones in the layers and represent what you might see in a typical river bed or delta today. Sandstone layers are literally made of sand sized stones as the name suggests! These therefore look much finer to the eye and have no big bits sticking out of the cliff face that you can see. Note also how some contacts between the conglomerate and sandstone layers are sharp and sudden, while others grade quite gradually between the different grain (stone) sizes. Why do you think that might be? What kind of sediment processes would form those different contacts?