Alberta badlands - glaciers, erratics, erosion and hoodoos

Cap rocks lead to hoodoo formations - but where do the cap rocks come from?

Alberta was once the site of a large inland sea (click here for an image).  Over millennia, suspended particles in the water settled to the bottom to form the thick clay deposits found in the interior of the province.  Uplifting through plate tectonics eventually drove the water away, but not before the fine silt caused many a dead prehistoric creature to be entombed and eventually fossilized.  Alberta is a rich source of remarkable fossils, many of which are on display at the Royal Tyrrell Museum in Drumheller.

The flattened, raised seabed would support millions of years of soil development and grasslands that would eventually give rise to the prairies.  A period of cooling led to the development of glaciers that tore through the Canadian Rockies and carried enormous quantities of gravel, rocks, and boulders across the plains.  When the glaciers melted, the rock burden was deposited as ground moraine.  Succession allowed the development of soil on these grasslands to produce the prairies we know today.

Rain allowed water to accumulate and flow along the Earth's surface.  Undulating streams carved deep canyons where they ran; meandering back and forth to carve out wide river valleys.  The moving waters would erode the soil, the moraine, and the clay, digging out deeper and deeper channels over time.  What's more, falling rain would hit the exposed clay surface and carry off tiny particles of the friable material.  But it didn't happen everywhere exactly the same; some surfaces were protected.

The boulders, long since deposited by the glaciers, would protect the underlying layers of clay from erosion.  The area around the erratics would be carried away leaving columns to develop.  Today, we call these vertical spires hoodoos; each one with a protective glacial erratic atop it called a cap rock.

I think that is amazing.

Thanks for reading.

Eric Svendsen     www.ericspix.com