This EarthCache was placed under the guidelines of the National Park Service and is on public property. No physical cache has been placed. This is a US Fee Area so to access this area you are expected to pay that fee or be a holder of a park pass. A side note – this earthcache is found along the Going-to-the-Sun Road. This road is closed typically from mid-October to early July, but that changes from year to year depending on snowfall, plowing, and weather conditions. Please check the conditions of the park and for any closures or postings at Current Conditions - Glacier National Park (U.S. National Park Service) (nps.gov) or Road, Trail & Campground Status - Glacier National Park (U.S. National Park Service) (nps.gov) for the most up to date information. In no way are individuals permitted into closed areas to access this geocache.
Please be advised that besides the geocache being located inside a fee area, during peak months there may be other requirements for entrance, like vehicle reservations.
Waterton-Glacier International Peace Park and World Heritage Site spans the northern Rocky Mountains along the United States-Canada border. The combined site includes snow capped mountains, high-altitude lakes, and rivers fed by glaciers. The landscape features glacial landforms, well-preserved fossils, striking rock formations, and other geological formations of significant aesthetic value. In the United States, one of Glacier National Park’s major highlights is the Going-to-the-Sun Road. This earthcache is located on Going-to-the-Sun Road, at the Jackson Glacier Overlook. You can see Jackson Glacier from the parking area, or hike towards it along the trail to Gunsight Lake, which begins at Jackson Glacier Overlook. There is parking available on either side of ground zero.
Glaciation
The defining geological event in shaping this landscape began with a global cooling trend approximately 2 million years ago. The Pleistocene Ice Age saw large ice sheets repeatedly advance and retreat throughout the temperate regions of North America until about 10,000 years ago. In the area that would become Waterton-Glacier International Peace Park, ice advanced and retreated until probably melting completely about 12,000 years ago. During the ice advances, the lower valleys were filled with glaciers and only the very tops of the higher peaks were visible. The "rivers of ice" sculpted the mountains and valleys into a variety of landforms associated with major alpine and valley glacial action.
Even though the Pleistocene Ice Age glaciers are gone, the results of their passing are evident on the landscape. Massive u-shaped valleys, numerous cirque lakes or tarns, horns, cols, moraines, and aretes are but a few of the glacially carved landforms that contribute to the beauty of Waterton-Glacier International Peace Park.
Present-day glaciers at the park date back 7,000 years and reached their maximum extent at the end of the Little Ice Age, which extended from 1770 to 1850.
Formation of a Cirque
Glacial cirques are distinctive amphitheater-shaped hollows found in mountain ranges worldwide, formed through the gradual processes of glacial erosion. Typically situated high on mountainsides, these cirques are partially enclosed on three sides by steep cliffs, with the highest cliff often referred to as the headwall. The fourth side, known as the lip or threshold, is where the glacier flowed away from the cirque. Over time, cirques may contain tarns—lakes formed by debris or moraine damming the basin—or may be occupied by a small glacier, known as a "cirque glacier," that forms within the cirque basin from a previous glacier.
Cirque and alpine glaciers originate high in the mountains, where they begin to flow downslope. From their high elevation origins, these glaciers may flow into ice falls, valley glaciers, or terminate within the mountains. In the Northern Hemisphere, this typically happens on the north-east slope of mountains, where the snow will be better protected from wind and the sun’s heat. Once filled with snow, the hollows begin to slowly enlarge by nivation – erosion of the ground around and under snow, primarily caused by alternate freezing and thawing. The snow in the hollow is slowly compacted by further snowfalls and – following phases of differing densities called neve and firn – eventually becomes glacial ice. This ice then deepens and widens the cirque through various erosion mechanisms.
The deepening of a cirque occurs primarily through abrasion and plucking. Abrasion happens when the glacier’s basal ice—formed by melting and refreezing at the ice-bed interface—grinds against the bedrock. This basal ice has a thin layer of water between the ice and the bedrock, allowing for basal sliding, which helps the glacier move more easily. As the glacier moves, it can pick up and carry debris, which enhances its erosive power. Plucking involves the glacier breaking off and removing chunks of bedrock from beneath, as cracks in the rock are expanded by the ice. Subglacial erosion is further promoted by meltwater, which flows through crevasses in the glacier and between the bedrock. These include the bergschrund (a deep crevasse at the head of the glacier that separates the moving ice from the snowfield at the head of the cirque), the randkluft (the gap between the glacier and the headwall), and other crevasses often caused by tension from different parts of the glacier moving at different speeds. This meltwater increases erosion by aiding subglacial plucking and abrasion, as well as contributing to freeze-thaw erosion. These combined processes gradually shape and enlarge the cirque, contributing to its characteristic bowl-like form.
Moraines, which are accumulations of glacial debris, also play a crucial role in cirques. As a glacier advances and retreats, it deposits debris along its margins and at the end of its flow path, forming terminal moraines, lateral moraines, and medial moraines. These features can dam tarns, mark the extent of the glacier’s advance, and help shape the cirque’s landscape by outlining the glacier's past positions and movements.
Jackson Glacier
From ground zero, you are able to view the Jackson Glacier, about 5.5 miles across the valley. Jackson Glacier was much larger during the middle of the 19th century, when it and Blackfoot Glacier to the east were one continuous ice body. Together they had a total surface area of more than three square miles. At that time, a tongue of the Jackson Glacier extended beyond the steep bedrock slope and into the forest below. The ice’s present position is a result of glacial retreat that started around 1860, as indicated by the age of the oldest trees now growing in the area once occupied by ice.
Repeat photography is a valuable tool for studying how glaciers in the park have retreated over the last century. Repeat photographs of the Jackson Glacier show the dramatic change the glacier has undergone since 1911. Initially, retreat rates appear to have been relatively slow, less than 25 feet per year until about 1910, when they seem to have increased. Once the glacier had retreated to the bedrock slope, during the mid-to-late 1920s, retreat became quite rapid. Not only did the glacier lose mass by melting, but large sections broke off and slid down the bedding surface, which was lubricated by melt water. The period of rapid retreat corresponds to a period of warmer summer temperatures and decreased precipitation in this region.
Questions:
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Describe how a glacier cirque is formed.
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What evidence of erosion are visible in the landscape? How has this glacier shaped the area?
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Do you believe that Jackson Glacier is the original glacier that formed this cirque? Why or why not?
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There is a display here with information on Jackson Glacier. Between 1966 and 2015, what percentage of Jackson Glacier melted?
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Optional: Take a photo of yourself or a “stand-in” (hat, GPS, etc.) with Jackson Glacier in the background.
Bibliography
Bendle, Jacob. "Cirques." AntarcticGlaciers.org. Bethan Davies. Last modified May 10, 2020. Accessed August 28, 2024. http://www.antarcticglaciers.org/glacial-geology/glacial-landforms/glacial-erosional-landforms/cirques/.
Bendle, Jacob. "Subglacial erosion." AntarcticGlaciers.org. Bethan Davies. Accessed August 28, 2024. https://www.antarcticglaciers.org/glacial-geology/glacial-landforms/glacial-erosional-landforms/subglacial-erosion/.
"Cirque." In Wikipedia. Accessed August 29, 2024. https://en.wikipedia.org/wiki/Cirque.
DooFi. Glacial Tarn Formation. Photograph. Wikipedia, May 18, 2008. Accessed August 29, 2024. https://en.wikipedia.org/wiki/File:Glacial_Tarn_Formation_EN.svg.
Elrod, M. J., L. McKeon, and Northern Rocky Mountain Science Center. Jackson Glacier in 1912 and 2009. 2009. Photograph. USGS Photographic Collection.
National Park Service. "Cirque and Alpine Glaciers." National Park Service. Last modified February 9, 2018. Accessed August 29, 2024. https://www.nps.gov/articles/cirqueandalpineglaciers.htm.
National Park Service. "How Glaciers Change the Landscape." National Park Service. Last modified February 9, 2018. Accessed August 28, 2024. https://www.nps.gov/articles/howglacierchangethelandscape.htm.
Phillips, Eleyne. "Glossary of Glacier Terminology." USGS. U.S. Geological Survey. Last modified January 12, 2013. Accessed August 28, 2024. https://pubs.usgs.gov/of/2004/1216/text.html.
Raup, Omer B., et al. Geology along Going-to-the-Sun Road, Glacier National Park, Montana. 2nd ed., Tucson, AZ, Glacier National Park Conservancy, 2018.