Case Studies
GL02, Glacial Landforms
Snowdonia (factors influencing landforms, landform interrelationships, change over time)
Case study facts: North Wales. Corrie = Cwm Idwal, Glacial Trough = Nant Ffrancon, Arete = Y Gribin, Ribbon Lake = Llyn Ogwen.
Factors influencing landforms:
Climate: temperature and precipitation control glacial formation, with colder climates promoting glacier accumulation and reducing meting, allowing glaciers to persist and erode landscape over longer periods of time. Loch Lomond stadial (11,500 years), colder conditions allowed valley glaciers to accumulate more mass.
Aspect: North and East facing slopes in Northern hemisphere receive less sunlight, which promotes greater snow retention, forming glaciers. Microclimates are also effected due to this. North facing corries are therefore more common (Cwm Idwal).
Geology: More resistant rocks are able to resist erosion, forming steep, rugged features, while softer rocks erode more easily leading to deeper troughs and ribbon lakes. Well jointed and faulted rocks are more easily eroded by plucking.
Landform interrelationships:
Cwm Idwal (corrie) feeds main glacier. corrie was accumulation zone, and ice flowing out becomes thicker, deepening the valley floor, and widening the valley into U shape.
U shaped valley and truncating spurs: valley glacier cut straight through interlocking spurs.
Roche moutonnees show ice movement and direction
Moraines are able to record glacier retreat
Change over time:
Minutes - rockfall might occur on aretes, in corries, and on the sides of pyramidal peaks.
Months - seasonal change to climate can speed up chemical and biological weathering. More ice can mean glacial advance in Winter.
Years - glacial erosion and deposition can create distinctive landscapes
100’s of Years - long term climate change can cause changes between valley glaciers and ice sheets.
1000’s of Years - rock structure and location can be changed by long term tectonic uplift and movement.
Laurentide Ice Sheet (factors influencing landforms, landform interrelationships, change over time)
Case Study Facts: Land of 10,000 lakes (actually 11,842). Tectonically tilted rock (alternates between weaker and softer rock, leading to differential erosion.
Factors influencing landforms:
Aspect: Determines directions of lobes, as cannot travel uphill. Minnesota high altitude, climate will be cooler, supporting extensive ice sheet rather than individual valley glaciers.
Climate: Last 150,000 years, temperatures averaged 8-9 degrees cooler than current interglacial. This allowed expansion of ice sheet from north. Lake Agassiz and Glacial River Warren - climate warming lead to widescale melting of the ice sheet, which created the proglacial lakes. Eventually flowed into sea through River Warren. Weight of ice being lifted at end of glacial period caused isostatic rebound.
Geology: Rate of erosion is dependent on resistance, particularly in the north east Arrowhead region, as the ellipsoidal basin is particularly deep here, due to less resistant shales. North Minnesota is part of the Laurentian Shield, so is underlain by alternating bands of resistant, igneous rock (granite), and weaker, sedimentary rock .
Landform interrelationships:
Drumlins and till sheets: glaciers smooth out till sheets into a Drumlin shape with pressure.
Ellipsoidal basin, and Lakes: great lakes are a highly eroded part of the basin, area of high erosion underneath the glacier, and the lowest area are now presently filled with water. Smaller lakes found in the less resistant shales in the arrowhead region of Minnesota in the north east. Kettle lakes are found within the basin, when part of ice sheet breaks off.
Scoured mountains and ellipsoidal basin: found in arrowhead in NE Minnesota, and caused by the heavy erosional impact of the ice sheet. The mountains and scoured mountain tops increase erosion upon the ellipsoidal basin by abrasion.
Change over time:
Minutes - mass movements on moraine complex and drumlns
Months - seasonal changes can lead to glacial retreats and advances, changing meltwater availability which can impact esker formation
Years - changes in level of Lake Agassiz, before and after draining events
100s of years - formation of lake agassiz, as retreat of Laurentide ice sheet
1000s of years - long term climate change (stadials and interstadials). Tectonic changes and isostatic rebound from glacial weight of ice sheet.
GL04, Human Activity in glaciated and periglacial landscapes
Prudhoe Bay (reasons for oil drilling, and impacts on the landscape)
Case study facts: Periglacial area (permafrost). 250 miles north of Arctic circle. North slope is very northernly part in America. Pipeline is 1,300km long.
Reasons for oil extraction: US has huge demand for oil (consumes 19.96 million barrels of petroleum products per day), due to dependence on fossil fuels, high carbon life styles, and a large population. Self-sufficiency is growing in importance, as energy dependency on different countries increases reliance, and can lead to negative diplomatic relations.
Impacts on landform and landscape: East of Prudhoe is Arctic National Wildlife Refuge, which could contain over 16 million barrels of oil, however, key carving ground for Caribou, and abundance of wildlife. Removal of vegetation decreases insulation, and can cause ground to collapse. Ognips and Alas lakes, as ice cores melt. Solifluction lobes created, as heat produced can cause permafrost melt, and longer period of melt for active layer. this increases movement, and uneven sinking in the ground. This can also cause mass movement, as wet soil moves downslope.
Impacts on flows of material: Permafrost is thawed as construction of infrastructure increases the input of thermal energy into the ground. Gravel, to insulate buildings, has come from nearby rivers, meaning less sediment can increase the erosion of the river. Urban heat island effect. Flaring (keeping flame alight), bad for environment, releases oil and gas into environment.
Impacts on flows of energy: Release and burning of gas releases large amounts of CO2, and higher levels of this contribute to global warming, further enhancing the greenhouse effect. Urban Heat Island effect, as urbanisation of area due to need for workers to live somewhere [town of Barrow, grown from 300 to 4600 in 100 years; mean temperatures on average 2.2 degrees higher than the surrounding rural areas]
Grande Dixence Dam (reasons for the dam, and impacts on the landscape)
Case Study Facts: Glaciated valley. Located in southwest Switzerland, at head of glacial valley called Val des Dix. Highest gravity dam in the world. Hydroelectric power makes up 62% of Swiss energy generation.
Reasons for dam: High demand from Switzerland for HEP, domestic supply of energy so not reliant on other countries, carbon neutral once built, doesn’t require production of fuels. Glacial landscape has high relief and high altitude, meaning limited human activity that had to be moved to create reservoir in valley. Steep sides of U shaped valley good for reservoir.
Impacts on landscapes and landforms: Built up sediment reduced flow of Borgne river, has led to higher concentration of pollutants from agricultural and domestic sources. Lack of discharge leads to some river channels practically drying up in Summer. Half of previous sediment flows into Lake Geneva. Sudden flooding decreases tourism.
Impacts on flows of material: Sediment builds up in reservoir as a result of low energy of water (and therefore it is deposited). Glacial meltwater flows are severely restricted and controlled, limiting formation of Glacial meltwater streams. Increased channel erosion.
Impacts on flows of energy: Energy is stored as GPE in reservoir, when dam is opened, GPE converted to KE, as flows down slopes. Due to transfer of energy, water becomes more erosive beyond the dam.