Inky black shards of volcanic glass unearthed in Alberta are helping researchers trace the movements of Indigenous people across Western Canada centuries ago.
Hand-carved arrowheads and jagged spears made of obsidian, a sharp rock formed by volcanic magma, are remnants of vast prehistoric trade networks that once cut across western North America.
No volcano has ever erupted in Alberta, meaning every shard of obsidian found in the province was carried here. With X-ray technology, researchers can trace each piece back to its source.
A new paper examining artifacts unearthed from Alberta’s eastern slopes suggests bison hunting in the southern foothills and a vast exchange network along the province’s northern rivers helped distribute the stones across the province.
Archaeologist Timothy Allan, the report’s author, said he wanted to better understand Alberta’s role in a vast Indigenous trade network that once spanned more than three million square kilometres.
A single piece of obsidian likely changed hands many times.
“The sheer scale of obsidian trade tells us that likely millions of people were in contact with one another,” said Allan, who works with Ember Archaeology, an archaeology and historic resources consulting firm based in Sherwood Park, Alta.
“The scope of the trade network was way more massive than we thought.”
Understanding the journeys of obsidian artifacts can provide new insight into how people moved across the landscape and the complex cultural ties that shaped the continent centuries ago, Allan said.
“It’s definitely part of our role in reconciliation, as archaeologists, to help tell these stories.”
The research, published by the Archaeological Survey of Alberta, is the latest offering from the Alberta Obsidian Project, an ongoing collaboration of researchers and archaeologists examining the province’s vast obsidian record.
Chemistry sealed in time
Over the past decade, project researchers have studied and catalogued more than 1,200 Alberta obsidian artifacts.
The artifacts and the trade itself date back to a period between 13,000 and 300 years ago, before European contact.
More than 520 archaeological sites have been identified in the province. The eastern slopes, which stretch from the alpine slopes of the Rockies down to the foothills, offer the most specimens.
Fragments have been found at 285 archaeological sites in the region. Allan’s analysis examined 383 specimens originating from 96 sites.
Obsidian’s unique qualities made it valuable for the prehistoric peoples who used it, and for archaeologists today.
The sharpest naturally-occurring material on earth, it was prized by Indigenous peoples who carved it into cutting tools and weapons.
Each piece of obsidian, formed by volcanic magma, has a unique chemical signature. Using X-ray fluorescence, researchers can identify unique geochemical markers and confirm the provenance of each piece.
“It’s formed when a volcano erupts and lava cools really, really quickly,” Allan said. “Because it cools so quickly, it kind of seals its chemistry in time.”
Each piece is bona fide proof of a long-distance exchange in the past, Allan said.
“If you find obsidian, you know that that material has travelled a long way.”
Distinct trade routes
Allan said Alberta appears to be the northern edge of the trade network, which stretched across the American midwest as far south as Texas, and into Canada as far north as what is now Fort McMurray, Alta.
Artifacts found in Alberta have travelled between 400 and 1,200 kilometres, with the vast majority coming from Bear Gulch in Idaho and Obsidian Cliff in Wyoming’s Yellowstone National Park. Other sources include the Anahim Peak and Mount Edziza sites in B.C.
Bear Gulch specimens accounted for 62 per cent of all samples. Obsidian Cliff examples made up about 30 per cent.
But the data suggests the trade routes were distinct from each other, with the North Saskatchewan River and the Red Deer River acting as natural boundaries between the trade routes.
People in what is now northern Alberta were more connected with tribes to the west, while people in the south were more closely tied with other tribes who lived on the open plains of the southern foothills.
In the north, trade appears to have been more sporadic, with obsidian likely moving into Alberta from B.C. along large east-west river networks that cut through the Rockies.
To the south, communal bison hunting seems to have shaped the trade.
Obsidian in these regions was traded in comparatively larger quantities and the exchanges appear to be part of a broad social network shared by people who lived and harvested together on the plains of what is now southern Alberta and the American Midwest.
Much of the obsidian uncovered in southern Alberta originates from sources south of the border. Bison jumps — where herds were driven off cliffs during large culls — account for some of the highest concentrations of obsidian artifacts in the province.
A portal into the past
Todd Kristensen, a regional archaeologist with the Archaeological Survey of Alberta, said the data has drawn out meaningful patterns about how people were sharing the land and resources.
“We can use obsidian to understand how different Indigenous groups in different ecological regions adapted to the landscape differently,” Kristensen said.
“It’s one of those little portals that we can use to understand how people adapted.”
Alberta’s obsidian record is uniquely positioned to provide a view of the past. The research offers a rare glimpse of the ties between various Indigenous peoples, Kristensen said.
He said more research is needed to understand the cultural significance of these prehistoric kinship connections — and the stone itself — among Indigenous peoples.
“Obsidian is fascinating because it tells us about human relationships,” he said. “That’s really rare for archaeologists to find.”
