Glacial Retreat Causes A Yukon River to Disappear

Posted by on Dec 14, 2016

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Much to the alarm of Canadians, the glacier-fed Slims River has disappeared following extensive glacial melting associated with anthropogenic climate change. Views of the Slims Valley, where the river once flowed, have been replaced by a dry plain, marked only by the sinuous bevels left behind by the river in the soil. These changes have major implications on local ecosystems and will inevitably result in lower water levels in downstream glacial lakes.

For example, for many years, the Yukon’s Kluane Lake has been fed by the continuous flow of the Slims River. Water in the Slims River had been transported from Kaskawulsh Glacier, feeding the Kluane Lake and flowing into the Bering Sea. The Kaskawulsh Glacier is a large temperate valley glacier that lies in the St. Elias Mountains. It measures more than four miles across at its widest, where it meets the Slims and Kaskawulsh Rivers. With the recent melting of the glacier, water has been diverted in the direction of the Kaskawulsh River, which drains nearly 500 kilometers away in the Gulf of Alaska.

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Map showing the re-routing of glacial meltwater. Previous route in green, current one in red (Source: Google Earth).

Jeff Bond of the Yukon Geological Survey stated to Paul Tukker of CBC News, “Folks have noticed this spring that the [river has] essentially dried up.” This loss of streamflow is the first regional occurrence in the last 350 years, according to the Yukon Geological Survey. Some of the warmest temperatures on record in 2015 and 2016 have had major implications on glacial health in the region, with ice loss reported throughout the surrounding Saint Elias Mountains, as reported by the National Oceanic and Atmospheric Administration (NOAA).

The rangers in the Kluane National Park noted that the Kaskawulsh Glacier has retreated nearly a half mile to the point where its melt water is now traveling in a completely different direction. In this case, the diversion of glacial meltwater is so substantial that no water is flowing in the direction of the Slims Valley and the downstream Bering Sea. Despite the Slims normally flowing approximately 19 kilometers from the edge of the glacier to Kluane Lake through the Slims Valley, changes to the Kaskawulsh’s spatial distribution have caused meltwater to flow not westward but to the east, flowing into the Pacific Ocean.

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A view across the expansive alpine lake in Kluane National Park (Source: James Bunt).

The change in water patterns has major implications for ecosystems in regions experiencing new levels of flow (both in the dryer and the now wetter areas). For example, in the absence of perennial water, the Slims Valley is more prone to dust storms, at least until new vegetation stabilizes the floodplain. Retired Utah Geological Survey geomorphologist Will Stokes told GlacierHub, “The valley may undergo a major ecological evolution over the next few decades, characterized by new flora and fauna.” Although this may seem like a minor adjustment, Stokes explained, “These changes can drastically alter the local food chain, and if lake levels end up lowering dramatically, there may be a major negative impact on local hunting and fishing.”

Jeff Bond further speculated to CBC News that the melt-water system which fed the Slims Valley may have only been a temporary outflow from the Kaskawulsh Glacier, representing a “300-year blip” on a much longer geological timescale in which large glaciers evolve. A study by Harold Borns in the American Journal of Science supports the notion that water began flowing northward around the year 1700, when climatological events caused the glacier to advance, ultimately diverting a large portion of snowmelt towards the Slims Valley and creating the Kluane Lake. This relationship illustrates the impact that regional climate has had on glacial events, with recent warming reversing the changes that occurred in a colder climate multiple centuries ago.

“Although it’s hard to tell how much lake levels in the Kluane will decrease, locals can expect an abrupt decrease in levels,” Stokes added, “followed by a much slower, long-term loss of water once levels stabilize.”

The Yukon Geological Survey postulates that water levels in Kluane Lake will lower by a meter or more in the foreseeable future. Although the Kluane National Park region is not densely populated by humans, lower water levels in the Kluane may stress trout and whitefish populations that are fished throughout the region’s warm months by both locals and visitors.

Although the diversion of water away from downstream communities may, in this case, be unsurprising to Yukon geologists in hindsight, it does shed light on the powerful effects of warmer temperatures and evolving climate dynamics on natural landscapes. The flow of rivers and plentiful caches of freshwater that exist in many regions due to glacial activity may be at serious risk as melting continues and water flow is redistributed.

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The Slims River West Trail running along the receding Kaskawulsh Glacier (Source: Dan Arnold).

It is difficult to tell how quickly changes like those that have occurred in the Yukon may happen in the future, yet these events may serve as a microcosm for the forthcoming state of glacial systems in light of anthropogenic climate change. Despite the ongoing study of glacial evolution by earth scientists, events like this in the Yukon really catch the attention of locals and illustrate first hand the effects of living in a warmer world.

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