The British Mountains of Ivvavik / by Sam Cornish

In Inuvialuktun, Ivvavik means nursery, and so it is for porcupine caribou, who calve on the coastal plains every year. But step up from the plains and foothills into Ivvavik’s British Mountains, and you enter a landscape made over timescales that exist in a different conceptual space to lifetimes. As a nursery epitomises youth, this landscape epitomises age - it is a museum to geological processes and millions of years of landscape evolution. A museum stewarded by grizzly bears and illuminated by the clear Arctic sun.

 The Firth River is met by perpendicular-flowing tributaries in the  Aufeis Reach

The Firth River is met by perpendicular-flowing tributaries in the Aufeis Reach

The Firth River, which cuts down through the British Mountains, holds claim to be the oldest river in Canada. While most of Canada was being reshaped by the enormous Laurentide Ice Sheet, the Firth continued unabated, for it flowed over unglaciated land. During the geologically recent glacials of the Pleistocene, sea levels were as much 120 m lower than today. Siberia was linked across the Bering Strait in a cold union to Alaska and the Yukon, making up a swathe of land known as Beringia. Large parts of Beringian land escaped glaciation by remaining high and dry. Though cold, Ivvavik’s British Mountains were sheltered from moisture to the south and west by coastal mountain ranges, and stayed above the spread of glacial ice from the east by virtue of altitude. During glacial periods, this was a land of woolly mammoths, giant beavers and sabre-tooth cats; your full Ice-Age cast, plus a few unusual extras like the saiga antelope.

 Clouds gather over the British Mountains

Clouds gather over the British Mountains

The Firth’s history may even outlive these glacial periods. The fact that the Firth cuts a river valley perpendicular to the strike of the bedrock suggests that it incised hand-in-hand with the most recent episode of mountain uplift in the region c. 70 - 45 Myr ago.

 The Firth River flows across the geological grain

The Firth River flows across the geological grain

Rafting down the river would be a geologists’ dream, hurtling through a perfectly exposed succession of folded and faulted rocks, spanning seven hundred millions of years of depositional history and two episodes of major mountain building.

 A rafting party alight at Sheep Creek

A rafting party alight at Sheep Creek

The story begins with the breakup of an ancient supercontinent called Rodinia c. 700 Myr ago, plunging Ivvavik into a marine basin. Pressure rises as North America assembles at c. 400 Ma, compressing Ivvavik in the so-called Innuitian mountain building*. Next, a sudden hiatus as Ivvavik presides above sea level, shaped by erosion. The story recommences with reclamation by the sea in the late Carboniferous Period, and fluctuating relative sea levels through the Permian to Jurassic, leaving thin layers of colourful sandstones and limestones. Tension then enters the narrative - the Arctic Ocean begins to grow, involving major extensional faulting of the crust. By 100 Myr ago, we find Ivvavik on the shores of the Western Interior Seaway, connecting the Arctic to the Tropics and a favourite hangout for large dinosaurs. The blueprint for today’s Ivvavik is then established with mountain growth in the late Cretaceous and early Cenozoic, as the Kula Plate is entirely subducted at a shallow angle below Alaska and Canada, sweeping island arcs into the continent. In the Tlingit language**, Kula means ‘all gone’.

 Folded and faulted rocks exposed in the Firth River gorge

Folded and faulted rocks exposed in the Firth River gorge

Above the river gorge, interlocking pyramidal mountains form ridge lines of cool pastel shades, punctuated by frost-shattered tors of limestone. These tors are the artefacts of a larger bedrock mass subject to variable rates of weathering, leaving pinnacles and ridges proud above the retreating slope.

 Limestone tors project above the ridgeline

Limestone tors project above the ridgeline

Bone-coloured lobes of soil gradually creep down slope in a process known as solifluction. These lobes thaw in the summer and slip, saturated with water, over perennially ice-fastened ground.

 Solifluction lobes deliniate the topographic gradient

Solifluction lobes deliniate the topographic gradient

Even in summer, ice still persists in the higher reaches of the river valley. This is ‘aufeis’, formed as groundwater seeps out above the permafrost, and freezes on the surface. New ice obstructs groundwater, which eventually spills out above existing ice, to form successive ice sheets up to several metres in thickness combined.

 Persistent aufeis in the middle distance

Persistent aufeis in the middle distance

Though it is old, each year Ivvavik blooms into new life out of the dark whiteness of winter. Valleys and alluvial plains are adorned with grass that is golden green in sunlight, and scattered with spruce trees. Umber and terracotta mosses gather where moisture pools. Moose potter around by lakes, muskoxen splash water on their shaggy undercoats as they cross streams, bears snack on abundant berries of black, red and blue, and wolverines escape detection by all but the eagles above.

 Spruce trees grow where they can get a foothold in the permafrost ground

Spruce trees grow where they can get a foothold in the permafrost ground

An idyllic picture does, however, do a disservice to the struggles that these animals endure. In late Spring, the Porcupine Caribou herds etch trails across the high slopes of Ivvavik as they press on in single file through snow to their coastal nursery. The calving caribou attract relentless predation from bears, wolves and eagles, and they are feasted upon by swarms of mosquitos so dense they can asphyxiate resting caribou. Seeking relief, they turn to the mountains and the frigid temperatures of their overwintering grounds again, completing the longest migration of any land mammal, tracing 2,400 km over Alaska and NW Canada.

On these annual crossings, the caribou etch fresh wrinkles on the face of an ancient landscape.

 Caribou trails converge on an opening in the ridgeline

Caribou trails converge on an opening in the ridgeline

Ivvavik remains a pristine wilderness. Only about 100 human visitors step foot inside its 10,000 square km range each year. By comparison, 641 people summited Everest in 2016. An unlikely (though it transpires, necessary) place, to find an international airport. Thanks to its protected status and sheer isolation, however, Ivvavik will hopefully long thrive as a world of two timescales - the annual flashes of life, and the slow evolution of a mountain belt.

 An unlikely place for an international airport

An unlikely place for an international airport

 Sheep Creek's runway

Sheep Creek's runway

* Literature is very sparse for Ivvavik’s mountain building record and sources diverge on what the extent of the Innuitian Orogeny was, and what the continental configuration was at the time.

**The Tlingit are indigenous people of the Pacific northwest coast of North America

For more on the science and sights of Ivvavik, check out the Parks Canada guide to the Firth River Valley: http://parkscanadahistory.com/geology/firth-river-valley.pdf