13.1 Glacier Formation and Types
6 min read•july 30, 2024
Glaciers, massive ice bodies formed over centuries, shape our planet's landscapes. They require specific conditions to develop, including cold temperatures and abundant snowfall. Understanding glacier formation and types is crucial for grasping their impact on Earth's surface.
Alpine and continental glaciers are the two main types, each with unique characteristics. Alpine glaciers carve mountain valleys, while continental ice sheets cover vast landmasses. These icy giants play a vital role in Earth's climate system and water cycle.
Glacier Formation Conditions
Climatic Requirements
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- Glaciers form in areas where annual snowfall exceeds annual snowmelt, leading to a persistent of snow and ice over many years
- Glacier formation requires consistently cold temperatures, typically below freezing for most of the year, to prevent significant melting of accumulated snow and ice
- Sufficient precipitation in the form of snow is necessary to build up the mass of the glacier over time, with the amount varying depending on factors such as latitude, elevation, and local climate conditions
Geographic Factors
- Glaciers are more likely to form at high latitudes or high elevations where temperatures remain cold throughout the year, such as in polar regions (Arctic, Antarctic) or mountainous areas (Alps, Himalayas, Andes)
- Topography plays a role in glacier formation, with high-altitude basins, valleys, and plateaus providing favorable conditions for snow accumulation and ice buildup
- The orientation of mountain slopes can influence glacier formation, with north-facing slopes in the Northern Hemisphere and south-facing slopes in the Southern Hemisphere receiving less direct sunlight, promoting cooler temperatures and reduced melting
Alpine vs Continental Glaciers
Alpine Glaciers
- Alpine glaciers, also known as valley glaciers, form in mountainous regions and are confined by the topography of the surrounding valleys and slopes
- Alpine glaciers are typically smaller in size compared to continental glaciers, with lengths ranging from a few hundred meters to several kilometers (Mer de Glace, France; Pasterze Glacier, Austria)
- The movement of alpine glaciers is influenced by the steepness of the terrain, with gravity causing them to flow downslope through valleys and basins
- Alpine glaciers often have a distinct accumulation zone at higher elevations and an zone at lower elevations, separated by the equilibrium line
- Examples of alpine glaciers include the Aletsch Glacier in Switzerland, the Baltoro Glacier in Pakistan, and the Malaspina Glacier in Alaska
Continental Glaciers
- Continental glaciers, also called ice sheets, are large masses of ice that cover vast areas of land, often spanning hundreds of thousands of square kilometers
- The two main continental glaciers in the world today are the Antarctic Ice Sheet and the Greenland Ice Sheet, which cover most of their respective landmasses
- Continental glaciers are not constrained by surrounding topography and can flow outward in all directions from a central dome or divide
- The immense weight and thickness of continental glaciers cause them to depress the underlying land surface, forming basins and altering the landscape on a large scale
- Continental glaciers can be several kilometers thick at their center and gradually thin out towards the edges, where they may terminate in ice shelves or calve into the ocean (Ross Ice Shelf, Filchner-Ronne Ice Shelf)
- During past glacial periods, continental glaciers covered much larger areas, including parts of North America (Laurentide Ice Sheet) and Europe (Fennoscandian Ice Sheet)
Snow Accumulation and Metamorphism
Accumulation and Mass Balance
- The process of glacier formation begins with the accumulation of snow in areas where snowfall exceeds snowmelt, leading to a positive mass balance
- Accumulation occurs primarily through direct snowfall, but can also include other processes such as wind-blown snow, avalanches, and hoarfrost formation
- The rate of snow accumulation varies depending on factors such as latitude, elevation, and local climate conditions, with higher accumulation rates generally occurring in maritime climates and at higher elevations
Snow Metamorphism
- Over time, the accumulated snow undergoes a process called metamorphism, which transforms the snow into denser, more compact ice
- Metamorphism occurs due to the pressure exerted by the weight of overlying snow, causing individual snow crystals to deform, break down, and recrystallize into larger, more tightly packed ice grains
- As the snow compacts and recrystallizes, air spaces between the grains are reduced, increasing the density of the snow and eventually turning it into solid glacial ice
- The transformation of snow into glacial ice through metamorphism typically takes several years to several decades, depending on factors such as the amount of annual snowfall, temperature, and the presence of meltwater
- Firn is an intermediate stage in the metamorphism process, characterized by partially compacted snow that has survived at least one summer melt season but has not yet fully transformed into glacial ice
- Firn has a density between that of fresh snow and glacial ice, typically ranging from 400 to 830 kg/m³
- The presence of a firn layer is important for the survival of glaciers, as it helps to insulate the underlying ice and reduce surface melting
Glacier Zones
Accumulation Zone
- The accumulation zone is the upper part of a glacier where annual snowfall exceeds annual snowmelt, resulting in a net gain of snow and ice mass
- The accumulation zone is typically located at higher elevations where temperatures are colder, allowing for the preservation and buildup of snow
- The boundary between the accumulation zone and the ablation zone is called the equilibrium line, which represents the point where annual accumulation equals annual ablation
- Snow accumulation in this zone occurs through direct snowfall, wind-blown snow, and avalanches, which gradually compacts and transforms into glacial ice through metamorphism
- The accumulation zone is essential for maintaining the mass balance of a glacier, as it provides the necessary input of snow and ice to offset losses in the ablation zone
Ablation Zone
- The ablation zone is the lower part of a glacier where annual snowmelt and ice loss (ablation) exceed annual snowfall, resulting in a net loss of glacial mass
- Ablation processes in this zone include melting, sublimation, and calving (the breaking off of ice chunks at the glacier's terminus)
- The ablation zone is typically located at lower elevations where temperatures are warmer, promoting increased melting and ice loss
- Surface meltwater in the ablation zone can form supraglacial streams and rivers, which may eventually flow into moulins (vertical shafts) or crevasses, transporting water to the base of the glacier
- The size and extent of the ablation zone can vary depending on factors such as climate, elevation, and the glacier's overall mass balance, with a larger ablation zone indicating a negative mass balance and potential glacier retreat
Glacier Terminus
- The terminus, also known as the snout or toe, is the lowest end of a glacier where the ice stops and melts or calves into water (for tidewater glaciers)
- The position of the terminus can advance or retreat over time, depending on the balance between accumulation and ablation processes in the glacier system
- A retreating terminus indicates that ablation is exceeding accumulation, resulting in a net loss of glacial mass, while an advancing terminus suggests the opposite
- The terminus of a land-terminating glacier may be marked by a distinct ice cliff, where the glacier ends abruptly and melts, forming a proglacial lake or stream
- Tidewater glaciers, which terminate in the ocean, often have a calving front at their terminus, where large chunks of ice break off and form icebergs (Jakobshavn Glacier, Greenland; Hubbard Glacier, Alaska)
- The behavior and dynamics of the glacier terminus can provide important insights into the overall health and stability of the glacier, as well as its response to changing climatic conditions
Key Terms to Review (18)
Ablation: Ablation refers to the process of removal or reduction of material from the surface of a glacier, primarily through melting, sublimation, and calving. This process plays a crucial role in the dynamics of glaciers, influencing their mass balance and overall health. Understanding ablation is key to grasping how glaciers respond to climate change and how they interact with their surrounding environment.
Accumulation: Accumulation refers to the process by which snow and ice build up over time, contributing to the growth of glaciers. This occurs when more snow falls in a given area than melts or sublimates away during warmer seasons. Accumulation is a critical component in the lifecycle of glaciers, influencing their mass balance and overall dynamics, as it directly affects how glaciers advance or retreat in response to climate conditions.
Basal slip: Basal slip refers to the movement of a glacier sliding over its bedrock due to the melting of ice at the base caused by pressure and temperature changes. This process plays a significant role in the dynamics of glacier flow, as it allows glaciers to advance and retreat, shaped by environmental factors such as temperature and pressure. Understanding basal slip is essential for recognizing how glaciers interact with their underlying terrain and contribute to landscape formation.
Continental glacier: A continental glacier is a massive, thick sheet of ice that covers vast areas of land, primarily found in polar regions and high-altitude areas. Unlike alpine glaciers, which are smaller and confined to mountainous regions, continental glaciers can extend over thousands of square kilometers, influencing landscapes through processes such as erosion and deposition. These glaciers play a crucial role in the Earth's climate system and the hydrological cycle, reflecting significant changes in temperature and precipitation patterns.
Crevasse: A crevasse is a deep fissure or crack that forms in the surface of a glacier, resulting from the movement and stress within the ice. These features are significant indicators of glacier dynamics and are often found in areas where glaciers flow over uneven terrain, causing the ice to stretch and fracture. Crevasses can vary in depth and width, playing a crucial role in understanding glacier formation and behavior.
Deposition: Deposition is the geological process in which materials, such as sediment, soil, and rocks, are laid down or accumulated in a new location after being transported by wind, water, or ice. This process is crucial for understanding how landscapes are shaped and altered over time, as it plays a key role in landform development and can significantly impact ecosystems and human activities.
Erosion: Erosion is the process by which soil and rock are removed from one location and transported to another by natural forces such as wind, water, and ice. This process plays a vital role in shaping landscapes and influencing various Earth systems through the movement of sediments and materials.
Glacial Budget: Glacial budget refers to the balance between the accumulation of snow and ice on a glacier and the loss of ice through melting, sublimation, and calving. This balance determines whether a glacier is advancing, retreating, or remaining stable, and is influenced by various factors such as climate, topography, and seasonal changes.
Ice flow dynamics: Ice flow dynamics refers to the study of how glaciers and ice sheets move and deform over time. This movement is influenced by gravity, temperature, and the physical properties of ice itself, as well as the underlying terrain and the presence of water at the base of the ice. Understanding ice flow dynamics is crucial for predicting glacier behavior, assessing climate change impacts, and interpreting glacial landforms.
Internal deformation: Internal deformation refers to the process by which a glacier undergoes changes in shape and structure due to the movement of its ice mass under pressure. This phenomenon occurs when the weight of the overlying ice causes the ice crystals within the glacier to deform, leading to flow and movement. It plays a crucial role in glacier dynamics, influencing how glaciers behave, their rate of movement, and ultimately, their contribution to landscape change.
Kettle lake: A kettle lake is a shallow, sediment-filled body of water formed by the melting of glacial ice. These lakes are typically found in regions previously covered by glaciers, and they can vary greatly in size and shape. Kettle lakes are an important feature of glacial landscapes, often indicating the retreat of glaciers and the processes of deposition and erosion that occur in these areas.
Little ice age: The little ice age refers to a period of cooler climate that lasted from approximately the 14th century to the mid-19th century, characterized by a significant decrease in temperatures in the Northern Hemisphere. This climatic phenomenon had profound effects on glacier formation and expansion, influencing glacial activity across many regions, as well as impacting agriculture and society during this time.
Moraine: A moraine is a landform created from the accumulation of debris and sediments that are deposited by a glacier as it moves and retreats. These formations can vary in size and shape, providing insights into past glacial activity. Moraines can be classified into different types based on their position relative to the glacier, such as terminal, lateral, and ground moraines, all of which play significant roles in understanding glacial landscapes.
Pleistocene Epoch: The Pleistocene Epoch is a geological time frame that lasted from about 2.6 million to 11,700 years ago, marked by repeated glaciations and significant changes in climate. During this period, large ice sheets covered substantial parts of North America, Europe, and Asia, shaping the landscape and influencing the formation of glaciers and various landforms. This epoch is critical for understanding Earth's climate history and the development of modern ecosystems.
Precipitation Patterns: Precipitation patterns refer to the spatial and temporal distribution of precipitation, including rainfall, snowfall, and other forms of moisture that fall from the atmosphere. Understanding these patterns is crucial because they influence various processes such as glacier formation, climate change, and ecosystem dynamics. Variations in precipitation patterns are shaped by factors like geography, atmospheric circulation, and climatic zones, making them vital to comprehending the behavior of glaciers and their types.
Serac: A serac is a large block or pillar of ice that forms on the surface of a glacier, typically found in areas where the glacier is steep or has undergone significant melting. These formations can be quite dramatic and unstable, often resulting from the process of differential melting and crevasse formation within the glacier. Seracs are important indicators of glacier dynamics and stability, reflecting the environmental conditions affecting glacial movement.
Temperature Gradient: A temperature gradient refers to the rate of temperature change in a specific direction over a given distance. In the context of glacier formation, this concept is crucial as it influences the physical properties of ice and snow, affecting processes such as melting, freezing, and the overall stability of glaciers. Understanding temperature gradients helps to explain variations in glacier behavior and formation, particularly in relation to altitude and climatic conditions.
Valley glacier: A valley glacier is a type of glacier that flows down a valley, typically between mountains, and is formed from accumulated snow and ice. These glaciers are often found in mountainous regions and can carve out U-shaped valleys as they move, shaping the landscape significantly. Valley glaciers can vary in size, but they are generally narrower than other types of glaciers, like ice sheets, and they are influenced by the topography of the terrain through which they flow.