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NatureSpeak Articles

The Wild West—Chaos at the end of the Ice Age. The demise of the Cordilleran Ice sheet and the birth of British Columbia as we know it

The earth warmed, the ice sheets melted pouring cold fresh water into the sea and the glaciers retreated to their mountain strongholds where they are doggedly hanging on. Photo: Wedgemont Glacier Photo by: Steve Carney

The last Ice Age had a profound impact on the Western Canada we know today.

For almost 2 million years, the Cordilleran ice sheet covered most of B.C. and the Yukon territory with a two- to three-kilometre-thick sheet of ice, which helped lower global sea levels and facilitated human migration into North America. Then, about 16,500 years ago, a period of global warming had a dramatic impact, sending the ice sheet into a rapid and terminal decline—and glaciers back into their mountain strongholds.

The effects of this relatively sudden upheaval were epic in scope and scale. Besides the usual earthquakes, flooding, landslides and volcanicity associated with British Columbia, there were also incredible crustal readjustments as well as sea level and climate changes. The interaction of land uplift and sea-level change was complex, and changed the configuration of the Salish Sea coastline through time as new land was added or lost to the sea. Interestingly, in their oral history, the Coast Salish Squamish (Skwxwú7mesh) people refer to a period known as “sxwexwiyam,” the “Mythical Time” or “early time when things were in chaos.”

Simon Fraser University professor Rudy Reimer, himself a member of the Squamish Nation, and other academics have associated this period with these immediate post-glacial times.

It must have been a wild ride as the ice melted, fresh water poured into the oceans, and global sea levels rose. At the same time, the land bounced back, rising quickly, free from the weight of the ice. In many places, this “isostatic rebound” outstripped the rising sea levels, and in some parts of B.C., relative sea levels dropped rapidly at an impressive rate of one metre every 10 years. Sea-level rises also had a big impact, and about 12,000 years ago sea levels rose by about 200 metres in the Howe Sound (Átl’ka7tsem), causing the Squamish River delta to migrate 50 km up river, before eventually dropping down to the current level.

When the ice retreated it exposed the beautiful, dramatic, wild and rugged environment we see today. Photo: Blackcomb Mountain looking towards Whistler and The Black Tusk. Photo by: Stephen Carney

Deglaciation also liberated a lot of sediment off the continent, ground out by the glaciers over the millennia. Much of the heavily populated greater Vancouver land area did not exist 10,000 years ago before glacial melt water streams deposited sediment at the mouth of the Fraser River, creating the Fraser Delta in the Strait of Georgia.

Climate did not change overnight, but rather stepped through a number of stages: from cool and moist, to warm and dry, and then a cooler period, before settling into something close to our current climate. This impacted post-glacial flora and fauna, creating a succession of plant and animal life and ecosystems changing through time in response to climate change.

Finally, about 5,000 years ago, everything had settled down, major isostatic and sea level changes had ceased, and the climatic conditions were similar to today. As custodians of their land, the resilient Coast Salish people thrived in tune with their environment, adapting to the conditions in the mountains and at sea. In the oral history of the Squamish people, this period is known as the “xaay xays” or the “Age of Transformation,” when the contemporary Salish Sea landscapes formed and everything in the world was put right.

Written by Stephen Carney


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