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Kaskawulsh Glacier and Slims River in 2016

View to the south of the Kaskawulsh Glacier’s north lobe and proglacial lake, which formerly drained into the headwaters of Slims River. Prior to late May 2016, the lake was about twice the size shown here, as indicated by the dashed line. The lake then partially drained to the east down the new channel (indicated by arrow) which has carved around the toe of the glacier, emptying into the Kaskawulsh River valley (out of view on the left side of the photo). The channels which formerly comprised the headwaters of Slims River are now occupied by the turquoise ribbons of standing water in the foreground. (Michael Schmidt photo, 16 July 2016).

Slims River flows about 20 km from the toe of Kaskawulsh Glacier to the south end of Kluane Lake, where it has formed a large delta. The river has historically been the main source of water input into Kluane Lake, which is the largest lake in the Yukon, but in late May 2016, the river was suddenly reduced to a trickle and remained that way for the rest of the year. Intense public interest in this story drove YGS to investigate the event in 2016 using reconnaissance flights and an analysis of hydrometric data and satellite imagery.

Until about 300 years ago, Kluane Lake drained south into Slims River, which flowed into the Kaskawulsh and Alsek river systems and ultimately into the North Pacific Ocean. At the peak of the Little Ice Age, in the late 1600s or early 1700s, the Kaskawulsh Glacier advanced across Slims River, blocking the south-flowing drainage of Kluane Lake, and forcing a reversal in direction of Slims River to the north (Clague et al. 2006; Reyes et al. 2006; Brahney et al. 2008). A new lake outlet was then established down Kluane River, at the north end of Kluane Lake. This drainage configuration still persists today with Kluane Lake now draining northward down Kluane River, ultimately flowing into Yukon River and the Bering Sea.

Since the end of the Little Ice Age, meltwater from Kaskawulsh Glacier has been the primary water source for both the Kaskawulsh and Slims rivers. In recent times, a large proglacial lake at the toe of the north lobe of the glacier collected much of this meltwater and drained into the headwater channels of the Slims River. However, in late May 2016, water draining the lake found a new path to the east, carving a diversion channel around the toe of the glacier, and emptying into Kaskawulsh River. What little water currently remains in the Slims River comes from smaller tributaries such as Canada, Bullion, Sheep and Vulcan creeks. Higher flows are not expected to return to Slims River because the new drainage channel is a more favourable pathway for water to flow, with a steeper gradient and lower elevation than the channels formerly feeding the Slims River. This type of diversion is known as river piracy, when one river captures the flow of another.

The drastic reduction in Slims River discharge caused Kluane Lake water levels to drop by over 1 m throughout the summer of 2016 (Water Survey of Canada). Analysis of Landsat 8 satellite imagery shows that several Kluane Lake tributary fan/deltas (e.g. Silver Ck, Gladstone Ck, Christmas Ck, Mines Ck, Bock’s Ck, Raft Ck, Talbot Ck and Brooks Ck) emerged or dried several hundred metres further offshore. Slims River delta dried up to 1.9 km offshore, dry spits near the head of Kluane River and Sandspit Point emerged up to 1 km offshore, and the head of Brooks inlet has significantly dried up for nearly 1.5 km.

The Slims River drainage shift had a number of significant impacts that were noted in 2016, many of which were far reaching. Boat access to Kluane Lake was seriously restricted, and considerably dustier conditions were experienced at the south end of the lake, where fine sediment from the dry delta surface is picked up by local winds. The lower lake levels have also resulted in lower flows down Kluane River, which may reduce habitat for an important chum salmon spawning node on the river. Conversely, the extra water flowing into the Kaskawulsh River also contributed to record peak flows on the Alsek River in summer 2016 (Water Survey of Canada), posing significant challenges to rafting operators.

The impacts of the Slims River drainage shift are expected to continue in the future and present an abundance of potential research opportunities in the region. Kluane Lake’s hydrological regime will shift from one dominated by glacial melt to one dominated by snowmelt. This will change the lake’s water balance, water chemistry and suspended sediment load. As vegetation colonizes the dried portions of the Slims River floodplain and delta, wildlife use in the area may also change, which is of particular concern for local bear and sheep populations.

Landsat 8 satellite imagery comparison of Slims River delta and floodplain, Kaskawulsh Glacier terminus, and upper Kaskawulsh River valley before (left; Aug. 3, 2015) and after (right; July 4, 2016) the Slims River was cut off from Kaskawulsh Glacier meltwater in May 2016. 

    For more information please contact:

    Panya Lipovsky - 867-667-8520

    Jeff Bond: 867-667-8514


    Brahney, J., Clague, J.J., Menounos, B., and Edwards, T.W.D., 2008. Timing and cause of water level fluctuations in Kluane Lake, Yukon Territory, over the past 5000 years. Quaternary Research, vol. 70, p. 213-227.

    Clague, J.J., Luckman, B.H., Van Dorp, R.D., Gilbert, R., Froese, D., Jensen, B.J.L., and Reyes, A.V., 2006. Rapid changes in the level of Kluane Lake in Yukon Territory over the last millennium. Quaternary Research, vol. 66, p. 342-355.

    Reyes, Alberto V., Luckman, Brian H., Smith, Dan J., Clague, John J., and Van Dorp, Richard D., 2006, Tree-Ring Dates for the Maximum Little Ice Age Advance of Kaskawulsh Glacier, St. Elias Mountains, Canada: Arctic, v. 59, no. 1, p. 14-20.


     Donjek Glacier  

    Donjek Glacier periodically dams the Donjek River producing glacial lakes such as the one shown here. Catastrophic drainage of these lakes is a hazard to the Alaska Highway, located 50 km downstream. Photo taken August 2, 2007.

    The St. Elias Mountains in southwestern Yukon are heavily glacierized. Glaciers pose a number of hazards. Crevasses, icefalls, ice avalanches, calving and loose and unstable moraines are significant hazards to recreationalists traveling across or near glaciers. In mountainous terrain, glaciers gradually erode away the bases of valley sides, making them steeper and more prone to large landslides that may travel several kilometers, such as the 2007 Mt. Steele landslide.

    Surging glaciers move up to one hundred times faster than normal for short periods every few decades. Surging glaciers can advance across rivers, damming temporary glacial lakes that eventually drain in sudden outburst floods or jokulaups. Over 100 glaciers in the St. Elias Mountains are classified as surging glaciers. Lowell Glacier and Tweedsmuir Glacier are two well known surging glaciers that flow into the Alsek River valley.

    Yukon Geological Survey collaborated with the U.S. Geological Survey, University of Ottawa and Parks Canada from 2010 to 2012 to monitor glacier dynamics (surging, retreat and calving activity) and baseline climatic conditions at the terminus of Lowell Glacier. YGS installed an automatic weather station, webcam and time lapse camera on a ridge above the southern flank of the glacier in 2010. This equipment operated until 2012. Links to related data are provided below

    Lowell Glacier

    Lowell Glacier is a large glacier located in Kluane National Park. It is approximately 70 km long and averages 5 km wide. The glacier terminates in Lowell Lake at approximately 500 m elevation, and about 60 km southwest of Haines Junction. The Alsek River flows into Lowell Lake from the north and exits the south end of the lake.

    Glacier surges are short periods of rapid glacier advance, likely caused by sudden changes in hydrological conditions beneath a glacier. Surging activity typically lasts for a year or two and occurs every decade or two. Lowell Glacier most recently surged in 2009-2010. Prior to that, Lowell Glacier surged in 1998-1999, 1983-1984, 1968-1970 and 1948-1950.

    At least five times in the past 3,000 years, Lowell Glacier has surged as far as Goatherd Mountain, damming the Alsek River and impounding a large lake that extended up the Alsek River valley to Haines Junction and into the Dezadeash River valley. This lake is referred to as “Neoglacial Lake Alsek”. The last time Neoglacial Lake Alsek formed was around 1850, at the end of the Little Ice Age. Neoglacial Lake Alsek also formed at least 3 times between about 1500 and 1800 A.D., and once more between 800 and 2900 years ago (Clague & Rampton, 1981). The largest of these lakes extended over 100 km, and reached depths of 200 m, making it possibly the largest Neoglacial lake in North America.

    Based on 1975-1979 discharge levels for Alsek River, it is estimated that once the Lowell Glacier dammed the Alsek River, the lake would have taken a year to reach Haines Junction, and over 5 years to reach its maximum extent. Eventually the glacier dams failed and each of the lakes drained catastrophically down the Alsek River into the Pacific Ocean at Dry Bay, Alaska. The floods produced giant ripples that are still visible in the Alsek River valley.

    Other evidence that provides a glimpse into the Neoglacial Lake Alsek history includes: staircase sets of raised beaches (visible from the Alaska Highway near Bear Creek), wave cut benches, driftwood layers along beaches, lichen density and size along river terraces, sequences of former lake sediments and buried soils, and the presence of ice-rafted erratics. A carved wooden paddle over 2 m in length was also found in the Alsek Valley (Clague & Rampton, 1981).

    Before the onset of the most recent (2009-2010) surge, the distance between the glacier terminus and the base of Goatherd Mountain on the opposite side of Lowell Lake was about 4 km. By late spring 2010, the glacier terminus had advanced up to 2.5 km past its pre-2009 position to within about 1 km of the base of Goatherd Mountain. Lowell Lake was choked with calved ice and made passage for Alsek River rafters a challenge.

    Even if the next surge causes the Lowell Glacier to reach Goatherd Mountain and dam the Alsek River, the lake will not likely flood Haines Junction. This is because the Lowell Glacier has thinned so much in the last century that it can not form a high enough dam to create a lake that would extend as far as Haines Junction.

    Yukon Geological Survey is currently collaborating with the U.S. Geological Survey, University of Ottawa and Parks Canada to continue monitoring long-term glacier dynamics (surging, retreat and calving activity) and baseline climatic conditions at the terminus of Lowell Glacier. In 2010, YGS installed an automatic weather station, webcam and time lapse camera on a ridge above the southern flank of the glacier. Links to these data are provided below.

    This time lapse video spans the time period: May 31 to August 6, 2010


    Tweedsmuir Glacier











    Tweedsmuir Glacier viewed from the location of the web camera installed to monitor the surge in 2007. Alsek River flows from right to left in foreground. Photo taken September 16, 2009.

    The terminus of Tweedsmuir Glacier is located 60 km further downstream on the Alsek River from Lowell Glacier. Between late 2007 and late 2008, Tweedsmuir Glacier surged at least 1.25 km. The glacier came within only a few hundred metres of blocking the Alsek River and threatened to block the Alsek River immediately above Turnback Canyon. If this had occurred, a lake on the order of 100 m deep would have been dammed which would have had major public safety implications for both Alsek River rafters and Alaskan residents in Dry Bay. The last time the Tweedsmuir Glacier surged to a similar position was in 1973 and 1974.

    In 2007 and 2008, YGS collaborated with the US Geological Survey to monitor the surge and maintain an early warning system consisting of a web camera which transmitted several images of the ice front per day via satellite. The camera was dismantled in September 2009.

    USGS – Tweedsmuir Glacier Surge
    Chris Larsen, University of Alaska Fairbanks - photos and laser altimetry surveys
    • Tobin, C., 2009. Galloping glacier reaches critical time juncture. Whitehorse Daily Star, Jan. 12, 2009.
    • CBC, 2008. Scientists keep close eye on surging Canadian glacier. CBC News, Dec. 30, 2008.
    • Rozell, N., 2007. Tweedsmuir Glacier surges toward the Alsek. Alaska Science Forum, Article #1878, Oct. 24, 2007.