THE HISTORY OF THE KASKUWULSH GLACIER AND ITS TERMINAL LAKES.
In the early Holocene Epoch (12000 to 11500 yrs ago), when the climate of southwest Yukon was warmer than today, Kluane Lake discharged to the south towards the Alsek River. The Kaskawulsh Glacier achieved its maximum extent between ~1717 and the mid-1750s. During this Little Ice Age advance, sediment from the glacier deposited an outwash fan, which raised the base level of a river that formerly drained south from Kluane Lake, perhaps through much of the Holocene. By the middle of the eighteenth century, the glacier completely blocked this south-flowing river, initiating the north-flowing Slims River (now known as the A’ay Chu), which rapidly built a delta and floodplain into Kluane Lake. The lake rose about 12 m above the 2006 datum and flowed over a debris fan at the north end of the lake, rapidly returning the lake to its present level. Kaskawulsh Glacier began to retreat in the nineteenth century, with retreat accelerating in the late twentieth and early twenty-first centuries. Between 1956 and 2007, for example, the glacier retreated 655 m. Roe et al. recently developed a method to test a glacier’s retreat against the null hypothesis that retreat was due to natural climate variability. Applying this analysis to the Kaskawulsh Glacier, we find there is only a 0.5% chance that retreat over the past century—and by extension, the observed piracy—could have happened under a constant climate. We therefore conclude that retreat of Kaskawulsh Glacier is attributable to observed warming over the industrial era.
Slims River (also known as A’ay Chu) hydrographs show a clear reduction in river levels apparent in May 2016. Normal diurnal fluctuations ended with an abrupt four-day drop in river level commencing on 26 May 2016. Over the remainder of the summer of 2016, the level of Slims River was 0.7–1.0 m below the average for those days. The reduction of Slims River flow has had substantial effects at Kluane Lake. The lake had a record minimum water level in early May 2016, about 0.1 m below its previously recorded low in May 2015. By the time of its normal seasonal peak (early August), the lake was ~1.7 m below its long-term mean level and 1 m below its lowest recorded level for that time of year. The lowering of Kluane Lake in 2016 equates to a volumetric reduction of ~0.67 km3 relative to the historic average.
WHAT HAPPENED TO CAUSE THE RAPID PIRACY?
About 15 mm of rain fell at Haines Junction on 2 May 2016, but there was little other precipitation during the first half of 2016. It is therefore unlikely that rainfall contributed significantly to the mid-summer increase in Alsek River discharge. Meteorological records from Haines Junction and the Kaskawulsh Glacier nunatak indicate that mean daily temperatures during the period January–April 2016 were, respectively, 4.3 °C and 3.6 °C warmer than the 2007–2016 decadal means for the same three-month period, which itself was probably the warmest decade of the past century. At Haines Junction, which is 300 m lower than the glacier terminus, mean daily temperatures were above freezing almost continuously after mid-March, approximately one month earlier than the decadal mean. At the nunatak, which is 1,000 m higher than the terminus, the main period of above-freezing conditions started in early May, ~1.5 weeks earlier than normal, and air temperatures were unusually warm immediately before the drop in the level of Slims River. It thus seems likely that Kaskawulsh Glacier experienced unusually high surface melt in the spring of 2016, which lead to development of an ice-walled canyon and increased flow in Kaskawulsh and Alsek rivers. The ice-walled channel that was established across dead ice at the terminus of Kaskawulsh Glacier was rapidly enlarged by meltwater and localized collapse of the channel walls in the summer of 2016, resulting in the 17 m lowering of Slims Lake. Even if the current canyon walls were to collapse and temporarily block the flow of meltwater into Kaskawulsh Lake, the blockage could not pond water in Slims Lake to the level required to re-establish Slims River. Only a re-advance of Kaskawulsh Glacier could block the channel and refill Slims Lake, but this is very unlikely given recent and current climate trends. We therefore conclude that the drainage change is permanent.
The piracy of Slims River has five important downstream implications. First, the level of Kluane Lake has fallen and may fall further, potentially below its outlet at the north end of the lake. If this happens, Kluane Lake will become a closed basin. Second, the large supply of sediment to Kluane Lake from Slims River has ended, with unknown effects on the structure and chemistry of the lake and its ecosystems. For example, in summer 2016, massive afternoon dust storms occurred almost daily on the nearly abandoned Slims River floodplain due to the lower lake level, possibly altering nutrient fluxes to the lake. Third, Slims, Kaskawulsh and Alsek rivers must now all adjust to altered discharges. For example, as flow and sediment transport in Slims River have decreased greatly, channel stability there may increase, resulting in conversion from a braided to a wandering or meandering river planform. Increased flows in Kaskawulsh River may increase sediment conveyance and bank erosion. Fourth, large-scale changes to drainage basin geometry and re-routing of meltwater may introduce considerable changes to fish populations and habitat, including effects produced by the timing of flows. Fifth, assuming that Kaskawulsh Glacier continues to thin and recede, Kaskawulsh River may advance its drainage headward (northward) into the easily erodible Slims River valley fill and towards Kluane Lake, thereby capturing the discharge of the small mountain streams that previously joined Slims River. It is noteworthy that the present head of Kaskawulsh River is ~25 m below the current level of Kluane Lake and, as a consequence, there is gravitational potential to drive continued expansion of the Kaskawulsh River catchment towards the lake. Thus, over time, headward erosion could result in Kaskawulsh River reaching the south end of Kluane Lake and re-establishing its former southerly drainage to the Pacific Ocean.
To log this Earthcache, answer the following questions by observing your surroundings near parking and send your answers to Tim Bits .
1. State the date and time that you are visiting this Earthcache.
2. Is there a pond South of you? If there is, estimate how wide the pond is from your location to the South side. If there isn't, is there any vegetation in the depression immediately to the South of you?
3. Kuane Lake is North of you. Estimate how far the Lake is from Hwy 1.
4. Using your GPS, what is the elevation of the water level?
5. There is mention above of dust storms when it is windy. Describe if there is any dust in the air or not.
6. At the waypoint listed coordinates (the bridge) – provide your observation – if there is a flow, which direction is it flowing? Into (North) or out of (South) Lake Kluane?
You are more than welcome to provide a picture of your adventure today on the cache page. Feel free to log your find at your leisure but understand that if you don’t contact me with the answers to the above questions, your log will be deleted.
Information provided from paper published in the journal of Nature; https://www.nature.com/ngeo/journal/v10/n5/full/ngeo2932.html