Tremendous forces shaped this landscape over millions of years. At different times this land was the floor of an ancient sea, a site where tectonic plates collided causing the upthrust of mountains, and part of the ice-free subcontinent during the last glaciation. Below are just a few features of interest from our geological story.
Much of our territory lies within Beringia. This was an ice-free refugium that remained unglaciated when most of North America was covered by thick sheets of ice during the last ice age. Beringia occupied a broad band of land across what is now Siberia, the Bering isthmus, Alaska, Yukon and the Northwest Territories. This cold, treeless plain – known as the mammoth steppe – was home to exotic animals such as woolly mammoths, steppe bison, camels, scimitar cats, short-faced bears and beavers the size of modern black bears. People also lived here and left remains of their campsites and tools which were found and dated by archaeologists some 10,000 years later. Klondike gold exists because of Beringia; there were no glaciers to break up and disperse the rich deposits of placer gold.
A major geological feature, the Tintina Trench, angles across our Territory from northwest to southeast. This is a wide rift valley formed along a fault line that, together with the Rocky Mountain Trench, extends all the way from Alaska to Montana in a remarkably straight line. It was formed by a slip-strike fault that has moved 425 km over 90 million years. The Tintina Trench is an important travel corridor for migrating birds. Hundreds of thousands of waterfowl, including Sandhill Cranes and Trumpeter Swans, use this “flyway” to reach their northern breeding grounds.
Much of our land is underlain by permafrost, a thick layer of soil that remains frozen year round for two or more years. The presence of permafrost can lead to the creation of interesting landforms such as:
ice lenses - large chunks of ice, some as big as cars
pingos - conical shaped, earth-covered mounds of ice
polygons - patterned ground shaped by permafrost and frost action
solifluction - the downslope movement of earth caused by frost action in areas with near-surface permafrost.
The presence of permafrost creates challenges when building roads, erecting buildings and putting up other infrastructure. The ground needs to be insulated so that the underlying permafrost won’t melt, softening the soil and causing tilting buildings, collapsing roads and other problems. One potential impact of climate change and rising temperatures, is damage to infrastructure due to melting permafrost.
The rugged mountains of Tombstone Territorial Park.
Illustration showing the extent of Beringia, the ice-free refugium of the last Ice Age.
Illustration by Midnight Arts
Frost mounds. Yukon Government photo.