Earth Surface Processes Unit 7 ReviewGlacial Processes and Landforms

Key Concepts and Terminology

• Glaciers form from the accumulation and compaction of snow over many years
• Glacial ice is a metamorphic rock composed of recrystallized snow
• Ablation refers to the loss of glacial ice through melting, sublimation, or calving
• The equilibrium line is the boundary where annual accumulation equals annual ablation
• Glacial mass balance is the difference between accumulation and ablation
• Positive mass balance occurs when accumulation exceeds ablation, causing glacial growth
• Negative mass balance occurs when ablation exceeds accumulation, causing glacial retreat

Formation and Types of Glaciers

• Glaciers form in areas where annual snowfall exceeds annual melting
• Snow accumulates and compacts into firn, then glacial ice over time
• Two main types of glaciers are alpine glaciers (valley glaciers) and continental glaciers (ice sheets)
• Alpine glaciers form in mountainous regions and flow downslope under the influence of gravity
  • Examples include the Mer de Glace in the French Alps and the Athabasca Glacier in the Canadian Rockies
• Continental glaciers are large ice masses that cover vast areas of land
  • Examples include the Greenland Ice Sheet and the Antarctic Ice Sheet
• Other types of glaciers include ice caps, ice fields, and cirque glaciers
• Glaciers can also be classified based on their thermal regime (temperate, polar, or subpolar)

Glacial Movement and Dynamics

• Glaciers move downslope due to the force of gravity and the pressure of the overlying ice
• Basal sliding occurs when meltwater lubricates the base of the glacier, allowing it to slide over the bedrock
• Internal deformation is the flow of ice within the glacier due to the weight of the overlying ice
  • The rate of internal deformation depends on factors such as ice thickness, temperature, and crystal orientation
• Glacial velocity varies spatially and temporally, with faster flow typically occurring in the center and during the melt season
• Crevasses are deep cracks in the glacial ice that form due to tensile stress
• Glacial surges are periodic rapid advances of glaciers, often caused by changes in basal conditions
• Ice streams are fast-moving channels of ice within an ice sheet, often bounded by slower-moving ice

Erosional Processes and Landforms

• Glacial erosion occurs through abrasion and plucking of the underlying bedrock
• Abrasion is the grinding of rock surfaces by debris-laden ice, creating smooth and polished surfaces (glacial polish)
• Plucking is the removal of large rock fragments by freezing and thawing of water in cracks and joints
• Cirques are amphitheater-shaped depressions carved by glacial erosion at the head of a valley
• Arêtes are sharp, knife-edge ridges formed by the erosion of two adjacent cirques
• Horns are pyramidal peaks created by the erosion of three or more cirques around a central peak (e.g., the Matterhorn)
• U-shaped valleys are characteristic of glacial erosion, with steep walls and a flat bottom
• Hanging valleys are tributary valleys that are left "hanging" above the main glacial valley due to differences in erosion rates
• Truncated spurs are the remnants of interlocking spurs that have been eroded by glacial action

Depositional Processes and Landforms

• Glacial deposition occurs when sediment is released from the ice through melting or lodgment
• Till is unsorted glacial sediment deposited directly by the ice
• Moraines are accumulations of till that form distinct landforms
  • Terminal moraines mark the maximum extent of a glacier
  • Lateral moraines form along the sides of a glacier
  • Medial moraines form where two glaciers merge
• Glaciofluvial deposits are formed by meltwater streams, such as outwash plains and eskers
• Glaciolacustrine deposits are formed in glacial lakes, such as varves (alternating layers of silt and clay)
• Erratics are large boulders transported by glaciers and deposited far from their source area
• Drumlins are elongated, streamlined hills formed by glacial deposition and shaping
• Kettle lakes form when buried ice blocks melt, leaving depressions in the landscape

Climate Change and Glacial Systems

• Glaciers are sensitive indicators of climate change, responding to variations in temperature and precipitation
• During glacial periods (ice ages), global temperatures are lower and glaciers expand
• During interglacial periods, global temperatures are higher and glaciers retreat
• The Pleistocene epoch (2.6 million to 11,700 years ago) was characterized by repeated glacial-interglacial cycles
• The Last Glacial Maximum (LGM) occurred around 21,000 years ago, when ice sheets covered much of North America and Europe
• Since the LGM, glaciers have been retreating due to natural and anthropogenic climate warming
• Glacial retreat has accelerated in recent decades due to human-induced climate change
• Melting glaciers contribute to sea-level rise and can impact water resources, ecosystems, and human activities

Field Techniques and Research Methods

• Glaciological fieldwork involves studying glaciers in their natural environment
• Ice coring involves drilling into glaciers to extract cylinders of ice for analysis
  • Ice cores provide valuable information about past climate, atmospheric composition, and glacial dynamics
• Ground-penetrating radar (GPR) is used to map the internal structure and thickness of glaciers
• GPS and remote sensing techniques (e.g., satellite imagery) are used to monitor glacial movement and changes in extent
• Mass balance measurements involve quantifying the amount of snow accumulation and ice loss over a given period
• Glacial geomorphology involves studying the landforms and sediments created by glacial processes
• Numerical modeling is used to simulate glacial dynamics and predict future changes
• Interdisciplinary approaches, combining geology, geography, physics, and climate science, are essential for understanding glacial systems

Real-World Applications and Case Studies

• Glaciers are important sources of freshwater for many regions, particularly during dry seasons
  • The Gangotri Glacier in the Himalayas is the source of the Ganges River, which supports millions of people in India and Bangladesh
• Glacial meltwater can be harnessed for hydroelectric power generation
  • The Grímsvötn Hydropower Project in Iceland uses meltwater from the Vatnajökull ice cap to generate electricity
• Glacial retreat can lead to the formation of glacial lakes, which pose risks of outburst floods (GLOFs)
  • The 1941 GLOF from Lake Palcacocha in Peru caused significant damage and loss of life in the city of Huaraz
• Glaciers are popular tourist attractions and support local economies through outdoor recreation activities
  • The Perito Moreno Glacier in Argentina is a major tourist destination, with walkways and boat tours allowing visitors to experience the glacier up close
• Studying glacial processes and landforms can help inform land-use planning and natural hazard assessment in glaciated regions
  • The Swiss Alps are a prime example of an area where glacial research is used to manage risks associated with glacial retreat, such as landslides and rockfalls
• Glacial deposits, such as sand and gravel, are important resources for construction and infrastructure projects
  • The Puget Sound region in Washington State, USA, relies heavily on glacial deposits for aggregate supply in the construction industry