Mount Cheops Cirque Glacier: Response of a Small Debris Covered Glacier to Climate Change
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Mount Cheops Cirque Glacier: Response of a Small Debris Covered Glacier to Climate Change S.J. Rubin V00197024 Geography 477, Field Studies in Physical Geography, University of Victoria. (E-mail: [email protected]) ABSTRACT Global climate change is evident in the alpine regions of British Columbia, effects of which were observed and explored during field school investigations of a microclimate cirque glacier on Mount Cheops in Glacier National Park of Canada. Rapidly receding glaciers are becoming an important water resource concern for British Columbia. We are beginning to understand that our water supply is not inexhaustible, similar to that realization regarding BC’s timber resources in the late twentieth century. Water is vital not only as a resource for human use; changes in glacial hydrological systems are also changing patterns of vegetation and wildlife that are adapted to alpine conditions. A hydrological survey was conducted to estimate the contribution of the Cheops glacial melt waters into the Connaught Creek drainage system, by comparing discharges at various locations along the valley bottom and within the cirque. Simple observations, such as water clarity and discharge fluctuations during the day, help to provide insight into the glacial hydrological system. Another particular consideration is the effect of debris cover in helping to preserve glacial ice, which was observed on more than half of the Mount Cheops glacier. Using a series of air photos, a temporal assessment of the Cheops glacier is made possible. There have been very few studies on small glaciers in the area, and the ones that have been done, including this one, are limited by being conducted in one location at one time. This project seeks to understand the significance of small glaciers and their role as water resources, and how debris cover slows the retreat rate of some glaciers. There is no inventory of the small glaciers that are disappearing, and basically no baseline study to build our knowledge upon. This paper will illustrate the importance of continued studies and monitoring of these crucial water resources, which are threatened by increasing global air temperatures, and other climate change variables. Keywords Cirque glacier; debris cover; microclimate; climate change BACKGROUND LOCATION Mount Cheops is located at the summit of Rogers Pass within Glacier National Park of Canada in the Selkirk Mountain range. The park is approximately 48 kilometers east of Revelstoke. Mount Cheops is accessed via the Balu Pass trail, with the trailhead at the Rogers Pass Visitor Center on the Trans-Canada Highway. The Selkirk Mountains are a prime example of interior rainforest, receiving approximately 2000mm of precipitation per year (Parks Canada). Compared with our 800mm on the coast in Victoria, we see that Glacier National park is very wet or very snowy all year round. The study site in the north Figure 1, Topographic map of Rogers Pass cirque of Mount Cheops is challenging to access, and includes bushwhacking a short distance through nearly impenetrable aspen groves, followed by scrambling up a steep boulder field until reaching the terminal moraine and beyond. SIGNIFICANCE OF CHEOPS ICE IN THE SELKIRKS The Selkirk Range and surrounding mountainous regions are extensively glaciated. There are a few large glaciers and ice fields, such as the Illecillewaet Nevé, but there are a vast amount of small patches of glacier ice. This is due primarily to the influence of microclimates produced in mountainous areas. The main requirement to produce a small microclimate glacier is a large north facing headwall, creating nearly constant shade on the slope below. The headwall also helps build deeper snowpack in the winter, because it is too steep for snow to stick to, creating avalanche accumulation on the slope below. These two factors Figure 2, False colour satellite image of the northern have helped to create the small SelKirk Mountains, blue is glacier ice. glacier on Mount Cheops, and many other glaciers in the region, and around the world. In this false colour image, compare the amount of large blue areas with the small blue areas. It can be argued that the accrued influence of all the small glaciers combine into a very important water resource. If the influence of the Mount Cheops glacier were studied on it’s own, it would be insignificant, so this study assumes that the Mount Cheops cirque glacier is representative of a type of glacier that is very common in the region, and that type of glacier’s combined abundance is a significant resource. The Cheops glacier is very small, about 1/1031 the surface area of the Illecillewaet Nevé, yet the Cheops glacial discharge is 1/8th of the Illecillewaet discharge measure during field school. It is also important to note the altitude of tongue of each glacier; the Illecillewaet Glacier terminus was at approximately 1975 meters above sea level this summer, compared to the Cheops tongue at about 1800 meters. The effects of microclimate at the Cheops glacier sheds light on this discrepancy. The disproportionate surface area to runoff is likely due to the difference in exposure of glacial ice to direct sunlight. The Cheops glacier is mostly in the shade and covered by insulating debris, leaving it susceptible to melt, due to warm air temperatures. The Illecillewaet Nevé, however, is entirely exposed to direct insolation, and is therefore susceptible to sublimation, or a direct phase change from solid ice to water vapour. This is a direct rational for believing that small microclimate glaciers are an important source of freshwater for river headwaters: they melt more than they evaporate, unlike the bigger glaciers in the region. MICROCLIMATE The Mount Cheops cirque glacier is greatly influenced by a unique geomorphic and climatic system. The temperature range in the region is very prone to lots of freeze/thaw cycles, which is essential for the weathering processes involved in cirque formation. “Cirques are often preferentially oriented according to the direction of solar radiation” (Graf, 1976). “Cirques result from two separate groups of processes: 1. Mechanical weathering and mass wasting, and 2. Erosion by cirque glaciers” (Ritter et al., 2002). The north side of the mountain has a very steep exposed rock headwall that descends from the summit down to a cirque valley that is occupied by the small glacier. The layout of this valley is consistent with descriptions of cirque formation and morphology. The large northern facing wall provides permanent shade on most of the glacier, with only a small portion of debris-covered ice extending far enough from the wall to receive direct sunlight at midday during the summer months. The headwall serves two functions in Figure 3, Base of last winter's avalanche cone on top of older deposits. the balance of the glacier; lots of snow falls on the wall, but it is too steep for snow to cling to during the winter months, avalanches deposit the snow from the wall down on the surface of the glacier, creating a large cone of snow at the edge of the headwall. The other function that the headwall serves is a source for debris cover. Alpine areas are subject to a strong freeze-thaw cycle, creating very extensive mechanical weathering in the area. The headwall is eroding almost constantly, and provides an enormous amount of debris to cover and preserve the glacier ice. DEBRIS COVER The Cheops cirque glacier is significantly influenced by the presence of debris cover. The debris is primarily composed of large angular boulders, but Figure 4, Debris cover high on the glacier, 450 meters below the head wall. there are areas of ice covered with fine silty sediments. There is an enormous amount blocky debris cover over a large area, creating landforms typical of rock glaciers. These landforms include arcuate ridges of debris and hummocky ablation moraines, which are consistent with findings at other rock glaciers, such as the Wenkchemna glacier in the Rocky Mountains (Gardner, 1977). The Cheops rock glacier feature is ice-cored, “containing subsurface ice with a superficial coating of rock fragments (up to several meters thick)… The coarse block layer may act as a thermal filter to protect the permanently frozen ice core if snow cover is thin or absent” (Ritter et al., 2002; Humlum, 1997). Gardner’s Wenkchemna paper also suggests that debris cover is responsible for creating a lag time in glacial activity relative to non-debris covered Figure 5, HummocKy ablation moraines indicate rocK glacier stagnation. glaciers in the region. The Wenkchemna glacier, for example, was estimated to lag 70 years behind other glaciers reaction time to climatic change. METHODS SITE SELECTION The Cheops cirque glacier was selected as a safe site to explore over the coarse of two daytrips. Other glaciers in the area are more difficult to access, and would have limited the amount of time at the site for observations. The Cheops cirque is located about 2 km from the Glacier Compound, and the Balu Pass trail allows close access to the site. The trail is along Connaught Creek, and accessing the cirque is easiest at the confluence of the cirque drainage creek into Connaught Creek. The drainage from the glacier descends a steep block field, with its loose and wet rocks, it is a dangerous area to travel through. A thin, active glacier is located in the cirque along the steep headwall, with ice extending over 1 km down slope from the wall. There was nearly constant rockfall all over the headwall, posing a hazard while exploring on the glacier. The Cheops cirque glacier proved to be a dynamic landscape, with changes noticed just between the two days. One change, for example, was the collapse of a snow bridge that was present over a crevasse on the first day, but was gone on the second day.