12.2 Glacial and periglacial processes and landforms
3 min read•july 22, 2024
Glaciers are powerful forces of nature, shaping landscapes through erosion, transport, and deposition. They carve out distinctive landforms like cirques, U-shaped valleys, and fjords, leaving behind evidence of their presence long after they've retreated.
Alpine and continental glaciers create different features, but both have profound impacts on the land. Periglacial processes in cold regions further modify landscapes, forming unique patterns and structures in frozen ground.
Glacial Processes and Landforms
Processes of glacial action
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- occurs through abrasion where glaciers drag rock fragments across bedrock surfaces, grinding and polishing the surface
- Plucking happens when glaciers freeze to the bedrock, then as the glacier moves, it plucks out entire chunks of rock
- Glaciers transport eroded material either within the ice (englacial) or on top of the glacier (supraglacial)
- takes place when glaciers melt or retreat, leaving behind unsorted sediment called
- Glacial consists of various sized sediments ranging from clay to boulders
- is sorted sediment deposited by meltwater streams (eskers)
Formation of glacial landforms
- Cirques are bowl-shaped depressions carved by alpine glaciers at the head of a valley through frost wedging and plucking of the headwall
- Arêtes form as sharp, knife-like ridges separating adjacent cirques when two or more cirques erode headward towards each other
- Moraines are accumulations of glacial till deposited by glaciers in different locations
- Terminal moraines are deposited at the end of a glacier
- Lateral moraines are deposited along the sides of a glacier
- Medial moraines form when two glaciers merge and their lateral moraines combine in the middle
Alpine vs continental glaciation
- Alpine glaciation occurs in mountain valleys and creates distinct landforms
- U-shaped valleys have a characteristic U-shaped cross-section due to glacial erosion
- Hanging valleys are tributary valleys left elevated above the main because of differences in erosion rates
- Horns are pyramid-shaped peaks formed by the erosion of multiple cirques around a mountain (Matterhorn)
- Continental glaciation involves vast ice sheets covering large areas of continents and generates unique landforms
- Fjords are steep-sided, U-shaped valleys that have been inundated by seawater (Sognefjord)
- Drumlins are streamlined, oval-shaped hills formed by glacial deposition
- Eskers are long, winding ridges of glacial deposited by subglacial streams
Periglacial processes and features
- is ground that remains frozen for at least two consecutive years
- Continuous permafrost covers an entire area
- Discontinuous permafrost is intermittent and patchy
- forms geometric patterns on the ground surface in periglacial environments
- are polygonal patterns formed by the freezing and thawing of water in the ground
- are circular arrangements of stones caused by frost heave and sorting
- is the slow downslope movement of water-saturated sediment in periglacial environments due to the freezing and thawing of the active layer above permafrost
Glacial impact on landscapes
- are parallel scratches or grooves on bedrock surfaces caused by abrasion from glacial ice, indicating the direction of past glacial movement
- are large boulders transported by glaciers and deposited far from their origin, providing evidence of past glacial extent and transportation
- Glacial lakes form through various processes
- form when buried ice blocks melt, leaving depressions in the landscape
- ###-dammed_lakes_0### form when moraines block the drainage of a valley
- is the uplift of the Earth's crust after the removal of the weight of glacial ice, resulting in raised shorelines and changes in sea level
Key Terms to Review (35)
Cirque: A cirque is a bowl-shaped, steep-walled depression found at the head of a glacial valley, formed by the erosion of rock and soil by glacial activity. These unique landforms are created as glaciers carve out the landscape, leaving behind a distinct shape that often contains a small lake or tarn at its base. Cirques are significant in understanding glacial processes and can indicate past climatic conditions when glaciers were more widespread.
Continental glacier: A continental glacier is a massive body of ice that covers extensive areas of land, typically found in polar regions and capable of altering the landscape through its movement and melting. These glaciers are much larger than alpine glaciers and flow outward from their thickest part, which is usually situated in the center. Their presence shapes various landforms and impacts local ecosystems.
Creep: Creep refers to the slow, gradual movement of soil or rock down a slope under the influence of gravity. This process can be influenced by various factors, including temperature fluctuations, moisture levels, and the freeze-thaw cycle. It plays a significant role in shaping landforms in both glacial and aeolian environments, affecting the stability and morphology of landscapes over time.
Drumlin: A drumlin is a streamlined, elongated hill formed by glacial activity, consisting of compacted till that has been shaped as glaciers move over it. These landforms are typically found in clusters and indicate the direction of past ice flow, providing insights into glacial movements and dynamics. Drumlins are significant in understanding glacial and periglacial processes as they reveal the interactions between ice sheets and the underlying landscape.
Esker: An esker is a long, narrow ridge of gravel and sand that is formed by the deposition of sediment from a stream running beneath a glacier. These features are significant in understanding glacial and periglacial processes, as they provide insights into the dynamics of glacial movement and meltwater flow. Eskers often indicate the paths that glacial meltwater took, highlighting how glaciers shape the landscape through their movements and the sediment they transport.
Fjord: A fjord is a deep, narrow inlet of the sea, typically surrounded by steep cliffs or slopes, formed by the submergence of a glaciated valley. These stunning geological features are often found in coastal areas that were shaped by glacial activity, where glaciers carved out valleys that later flooded due to rising sea levels. Fjords are significant as they showcase the processes of glacial erosion and provide insights into past climatic conditions.
Glacial deposition: Glacial deposition refers to the process by which materials, such as rocks and sediments, are dropped or laid down by a glacier as it moves and melts. This process is a key component of glacial dynamics, where the movement of ice transports various materials, shaping the landscape and forming distinctive landforms like moraines, drumlins, and outwash plains.
Glacial erosion: Glacial erosion is the process by which glaciers wear away the landscape as they move, sculpting the land through the grinding action of ice and the transportation of debris. This process is a major factor in shaping valleys, mountains, and other landforms, revealing the powerful impact glaciers have had on Earth's surface throughout geological history. The interaction between glacial movement and geological features results in distinct landforms that illustrate the dynamic nature of Earth's landscape evolution.
Glacial erratics: Glacial erratics are large boulders that have been transported and deposited by glaciers, often found far from their original source. These rocks can vary in size and composition and serve as important indicators of past glacial activity, helping to reconstruct the movement and extent of ancient ice sheets.
Glacial outwash: Glacial outwash refers to the sediment deposited by meltwater from a glacier, typically forming broad, flat plains or valleys downstream of the glacier. This sediment can include a mix of sand, gravel, and silt, resulting from the erosion and transport processes of glacial ice. The presence of glacial outwash is key to understanding glacial processes and the landscape changes they create.
Glacial retreat: Glacial retreat refers to the process where a glacier loses mass, resulting in its backward movement or reduction in size over time. This phenomenon occurs when the rate of ice melting and sublimation exceeds the accumulation of snow and ice, often driven by climate change, warming temperatures, or changes in precipitation patterns. Glacial retreat is crucial for understanding glacial dynamics and the broader implications for landforms and ecosystems shaped by glacial activity.
Glacial Striations: Glacial striations are scratches or grooves carved into the bedrock by the movement of glaciers as they advance and retreat. These features are created when embedded rocks in the base of a glacier scrape against the underlying rock surface, leaving behind distinctive marks that indicate the direction of glacial flow. The presence of glacial striations is an important clue in understanding past glacial activity and helps geologists interpret ancient climates and landscapes.
Glacial till: Glacial till is an unsorted mixture of sediment that has been deposited directly by a glacier as it melts. This sediment can include a variety of particle sizes, from fine silt to large boulders, reflecting the materials that were eroded from the landscape as the glacier advanced. The presence of glacial till provides important clues about the movement and melting patterns of glaciers and plays a critical role in the formation of various landforms created by glacial and periglacial processes.
Gps surveying: GPS surveying is a technique that uses Global Positioning System technology to determine precise locations on the Earth's surface. This method is especially useful in mapping and monitoring landforms, including those shaped by glacial and periglacial processes, providing critical data for understanding the dynamics of these environments.
Hanging Valley: A hanging valley is a small valley that is elevated above the main valley floor, often formed by the action of glaciers. These valleys typically end in steep cliffs or waterfalls and are a result of differential erosion where the tributary glacier erodes less than the main glacier, leaving the tributary valley hanging above the main one. This unique landform highlights the powerful processes of glaciation and landscape evolution.
Holocene Epoch: The Holocene Epoch is the current geological epoch that began approximately 11,700 years ago, following the last glacial period. It represents a time of significant climatic stability and warming, allowing for the flourishing of human civilizations and diverse ecosystems. The Holocene is characterized by notable changes in earth processes, including glacial and periglacial activities, which have shaped landscapes and landforms we see today.
Horn: A horn is a sharp, pyramid-shaped peak that is formed by the erosion of three or more glaciers converging at a mountain summit. This geological feature is often characterized by its steep, jagged ridges and pointed summit, creating a dramatic and iconic landscape often found in glaciated mountain ranges. Horns are significant because they highlight the powerful processes of glacial erosion and showcase the impact of climate on mountainous terrains.
Ice core analysis: Ice core analysis is a scientific method that involves extracting cylindrical samples from ice sheets or glaciers to study past climate conditions and atmospheric composition. This process reveals valuable data about historical climate changes, greenhouse gas concentrations, and volcanic activity, which helps scientists understand the Earth's climatic history and predict future trends.
Ice wedge polygons: Ice wedge polygons are distinctive landforms found in periglacial regions, characterized by the presence of ice wedges that form in the ground, creating a network of cracks and patterns resembling polygons. These features develop as a result of freeze-thaw cycles, where repeated freezing causes the ground to crack, and subsequent thawing leads to the accumulation of ice within those cracks, ultimately leading to the formation of these polygonal shapes.
Isostatic Rebound: Isostatic rebound is the process of Earth's crust rising after the weight of ice sheets or glaciers has been removed. When glaciers melt, the land that was compressed by the immense weight starts to slowly rise back to its equilibrium state. This phenomenon not only illustrates the dynamic nature of the Earth's surface but also has a significant impact on landscape features and sea levels in glacial and periglacial environments.
Kettle lakes: Kettle lakes are depressions that form in glacial landscapes, created by the melting of large ice blocks left behind by retreating glaciers. These lakes are typically round or oval-shaped and vary in size, often filled with water after the surrounding glacier melts. The formation of kettle lakes is a significant aspect of glacial processes, showcasing how glaciers shape the landscape and contribute to the development of unique landforms.
Moraine: A moraine is an accumulation of debris and sediment that has been transported and deposited by a glacier. These landforms are significant because they provide insight into past glacial activity and can indicate the direction of glacier movement. Moraines can vary in size and shape, with some forming long ridges while others create irregular hills, showcasing the powerful impact glaciers have on shaping the landscape.
Moraine-dammed lakes: Moraine-dammed lakes are bodies of water that form when glaciers deposit debris, known as moraines, which act as natural barriers to block the flow of meltwater. These lakes typically develop in glacial valleys and can provide insight into past glacial activity, as well as influence local ecosystems and hydrology. Understanding these lakes helps connect glacial processes with landscape evolution and sediment dynamics.
Outwash: Outwash refers to the sediment that is transported and deposited by meltwater streams flowing from a glacier. This process occurs as glaciers melt and produce large volumes of water that carry away fine sediments, resulting in the formation of distinctive landforms. Outwash is typically found in glacial landscapes, where it plays a crucial role in shaping the surrounding terrain and influencing the local ecosystem.
Patterned ground: Patterned ground refers to a distinctive arrangement of stones and soil on the surface of the ground that typically occurs in periglacial environments. This phenomenon arises due to freeze-thaw cycles that cause soil and rock to shift, creating unique geometric patterns such as circles, polygons, or stripes. These formations indicate past climatic conditions and are often associated with the processes of frost heave and solifluction.
Permafrost: Permafrost is a layer of permanently frozen ground that typically occurs in polar regions and high mountain areas, remaining at or below 0°C (32°F) for at least two consecutive years. This unique geological feature significantly influences the surrounding environment, affecting soil composition, vegetation patterns, and hydrology. The presence of permafrost also has important implications for climate change, as its thawing can release greenhouse gases like methane into the atmosphere.
Pleistocene Epoch: The Pleistocene Epoch, spanning from about 2.6 million to 11,700 years ago, is characterized by repeated glaciations and significant climate fluctuations. This epoch played a crucial role in shaping the Earth's surface through extensive glacial and periglacial processes, leading to unique landforms and influencing the development of various ecosystems.
Remote sensing: Remote sensing is the process of acquiring information about objects or areas from a distance, typically using satellite or aerial imagery. This technique allows scientists to collect data on various geological features, including landforms, mineral deposits, and tectonic structures, without direct contact. By analyzing these images and data, researchers can interpret and understand the Earth's surface and processes more effectively.
Solifluction: Solifluction is the gradual, slow movement of saturated soil down a slope, often occurring in periglacial regions where freeze-thaw cycles are prevalent. This process results from the melting of ice in the active layer during warmer months, causing the overlying saturated material to flow slowly under the influence of gravity. Solifluction plays a significant role in shaping landforms in cold climates and can contribute to the development of features like solifluction lobes and terraces.
Stone circles: Stone circles are prehistoric structures made up of standing stones arranged in a circular pattern. These ancient constructions are often associated with ceremonial and astronomical functions, reflecting the cultural practices of the societies that built them. Stone circles are commonly found in areas affected by glacial and periglacial processes, where the landscape has been shaped by ice movement and freeze-thaw cycles, contributing to their preservation and significance in understanding human interaction with the environment.
Surge: In glaciology, a surge refers to a rapid and often dramatic movement of a glacier, where it advances significantly over a short period. This phenomenon is characterized by a sudden increase in the glacier's flow rate, which can be caused by various factors such as changes in subglacial water pressure or the melting of ice. The effects of a surge can lead to the formation of distinct landforms and can significantly alter the landscape.
Thermokarst: Thermokarst refers to the irregular topography that develops in permafrost regions when ground ice melts, causing the ground to subside and form depressions, mounds, and unique landforms. This phenomenon is primarily driven by climate change and the warming of the Arctic, leading to the thawing of permafrost, which in turn disrupts the landscape and ecosystem dynamics in these areas.
Till: Till is a type of unsorted glacial sediment that is deposited directly by the ice as it melts. It consists of a mix of various-sized particles, including clay, silt, sand, gravel, and larger boulders, which are all jumbled together. The presence of till helps to characterize areas affected by glaciation and is crucial for understanding the processes and landforms shaped by glaciers.
U-shaped valley: A U-shaped valley is a distinct landform created by the erosive action of glaciers, characterized by its wide, rounded bottom and steep sides. This unique shape results from the intense scraping and carving of the landscape as a glacier moves through a pre-existing V-shaped valley, transforming it into a broader and flatter basin. These valleys are often associated with other glacial features such as moraines and fjords, highlighting the powerful role glaciers play in shaping the earth's surface.
Valley glacier: A valley glacier is a type of glacier that forms in mountainous areas and flows down valleys, typically following the pre-existing topography of the landscape. These glaciers can carve out U-shaped valleys, create cirques, and deposit glacial till, significantly shaping the surrounding geography. Valley glaciers are crucial in understanding glacial processes and their impacts on landforms, as they demonstrate the dynamic nature of ice movement and erosion.