Scientists have determined that a large volcano on the Yukon/Alaska border, known as Mount Churchill, exploded approximately 1,200 years ago.
Mount Churchill is one of the tallest volcanic peaks in North America, even though its top is missing. It is thought to be the most traumatic volcanic episode in North America in the past 2,000 years.
Between 25 and 50 cubic kilometres of ash were spewed into the air, making it 10 times greater than the explosion of Mt. St. Helens, and greater in magnitude than either Krakatoa or Mount Pinatubo.
In fact, it was an explosion almost a third of the size of Mount Tambora, which blew its top in Indonesia in April of 1815. Tambora was the deadliest volcanic explosion of the 19th century. More than 70,000 people died when it exploded and sent a plume of dust and ash 40 kilometres into the atmosphere. The fallout had a devastating effect upon the agriculture in the surrounding area.
As Tambora’s cloud of dust spread around the globe, it had a significant impact on global temperatures, causing crop failures, famine and disease as far away as North America and Europe. The following year was so cold that 1816 was known as “the year without summer.”
Carol Geddes, an award-winning Yukon filmmaker, interpreted the impact of this event in her animated film, Two Winters: Tales from Above the Earth, a story of how indigenous peoples in northern Canada fought to survive a year with no summer.
When Mount Churchill blew, the event must have been nearly as spectacular. The cloud of ash drifted eastward, covering an area of 250,000 square kilometres. You will see its effect even today as you drive to Dawson City. In the cutbanks along the Klondike highway north of Carmacks, you will observe the ash as a distinctive white layer a few centimetres below the ground surface. Samples of White River ash have been found in Germany and in peat bogs in Ireland.
The sound of the initial explosion would have been heard hundreds of kilometres away. The ash cloud would have been so dense as to darken the skies for several days. Similar explosions have been accompanied by lightning, thunder and heavy precipitation. It is believed that Churchill exploded in the winter, so this precipitation probably came down as snow.
Ash would have been deposited thickly over the entire landscape. The air would have been filled with microscopic fragments of volcanic glass and made noxious by sulfuric acid, sulfur dioxide, fluorine and chlorine. Any animal within this toxic rain would suffer from respiratory distress. Pools of carbon dioxide in low-lying areas would be lethal to any animal that ventured into them.
Plant life would have been covered in a thick layer of ash, inhibiting photosynthesis. Acid rain that followed would strip trees and plants of their foliage. The heavy load of microscopic volcanic glass particles that ended up in lakes and streams would have been deadly for the fish inhabiting those waters. These phenomena have been observed at the locations of other volcanic explosions, so it is speculated that similar events occurred here 1,200 years ago.
Many authorities believe that this toxic environment forced local inhabitants to leave the area. Oral traditions of Athapascan-speaking people in the Northwest Territories contain accounts of volcanic events and the discovery of copper that are believed to be derived from first-hand experience of the explosion of Mount Churchill and its after-effects, hundreds of kilometres to the west. This oral history has been passed down through succeeding generations for more than 1,200 years.
By comparison, scholars suggest that oral traditions in the Yukon contain stories about the origin of copper, but not of any volcanic event. This would be expected if new Athapascan-speaking people moved into the region after the volcanic explosion.
A remarkable similarity between linguistic features of the Navaho in the American southwest and Athapascan speakers from the Yukon and N.W.T. suggest a common origin over a thousand years ago. This has led experts to speculate that the modern-day Navaho are descended from people who fled the Yukon in the aftermath of the Mount Churchill explosion.
Before Christmas, I spoke with Greg Hare, senior projects archaeologist for the territorial government, about the impact of Mount Churchill upon Yukon prehistory. Hare has been working with archaeological material recovered from the ice patches located in the southwestern Yukon since the 1990s.
The artifacts and other remnants preserved in these natural, higher-elevation deep freezes have helped researchers gain a clearer perspective of what happened in the Yukon 12 centuries ago. He believes that the impact of the eruption was catastrophic on the plants, animals and humans living in the ash zone.
Study of DNA from caribou dung recovered from the ice patches has revealed that the pre-ash caribou population was replaced by a genetically different population after the ash fell. There may be a gap of as much as 100 years separating the two populations. This suggests that the local caribou population here at the time of the explosion either left the area entirely, or died off from the effects of the ash fall, and were later replaced by a new population.
Other research focussed upon Chironomids, tiny insects that are abundant in the Yukon lakes. Chironomids are a major source of food for Yukon fish stocks. This research determined that for a period of 60 to 100 years around the time of the volcanic event, Chironomid populations disappeared in lakes where the ash fall was greatest. If there was no food, then fish populations would have suffered.
Given the catastrophic events during and after the eruption, and the impact on major food sources in the ensuing decades, the Yukon would not have been the most desirable place to live.
The archaeological record reveals some dramatic changes occurring around the same time as the deposition of the White River ash. It was at this interface that the millennia-old traditional use of the atlatl, or throwing dart, was replaced in the Yukon by the bow and arrow. Bone and antler technology appear, and copper artifacts are found for the first time.
Fire-cracked rock, which results when rocks heated in a fire are repeatedly placed in a container in order to bring water to a boil, is found in abundance after the ash.
Was this the result of new people in the southwest Yukon, or just the introduction of new technology?
Combined, the geological, biological, linguistic, oral historical and archaeological evidence suggest that some significant changes occurred when the White River Ash fell upon the Yukon. Refining the picture of this significant event should keep researchers busy for years to come.
Michael Gates is a Yukon historian and sometimes adventurer based in Whitehorse. His latest book, Dalton’s Gold Rush Trail, is available in Yukon stores. You can contact him at firstname.lastname@example.org