13.2 Glacial erosion and depositional features
4 min read•july 24, 2024
Glaciers are powerful agents of erosion, shaping landscapes through processes like and . These icy giants carve out distinctive features in mountainous regions, from bowl-shaped to knife-edge and pyramid-like .
As glaciers move, they deposit material, creating various landforms. , , and are just a few examples of the diverse terrain left behind. These glacial deposits provide clues about past ice movements and climate changes.
Glacial Erosion Processes
Glacial erosion processes
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- Abrasion
- Rock fragments embedded in glacial ice scrape against bedrock creating smooth, polished surfaces (glacial polish)
- Produces fine-grained sediment called rock flour giving glacial meltwater its characteristic milky appearance
- Striations form parallel grooves in bedrock indicating direction
- Plucking
- Glaciers freeze onto loose rock fragments and tear them away as ice moves downslope
- Meltwater refreezes in cracks and crevices expanding and loosening rocks (frost wedging)
- Results in angular, jagged rock fragments transported within or on top of glacier
- Glacial quarrying
- Large-scale removal of bedrock blocks by glacier
- Occurs in areas of weakness in bedrock (joints, faults)
- Creates steep-sided valleys and fjords
- Meltwater erosion
- Streams flowing on, within, or beneath glacier erode rock and sediment
- Forms subglacial channels and potholes
- Contributes to formation of eskers and
Alpine glacier erosional landforms
- Cirques
- Bowl-shaped depressions carved into mountainsides by freeze-thaw weathering and plucking
- Often contain small lakes called tarns after glacial retreat
- Accumulation zone where snow collects and compresses into glacial ice
- Arêtes
- Sharp, knife-edge ridges between adjacent cirques formed by erosion of two glaciers flowing in opposite directions
- Can form when cirque headwalls erode back to meet
- Examples include Crib Goch in Snowdonia and Striding Edge in the Lake District
- Horns
- Pyramid-shaped peaks formed when three or more cirques erode towards a central point
- Created by the intersection of multiple arêtes
- Famous examples include Matterhorn (Switzerland) and K2 (Pakistan/China border)
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- Formed as glaciers deepen and widen pre-existing V-shaped river valleys
- Characterized by steep sides and flat bottoms
- Examples include Yosemite Valley (California) and Lauterbrunnen Valley (Switzerland)
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- Smaller tributary valleys left "hanging" above main glacial valley
- Form when main glacier erodes more deeply than tributary glaciers
- Often result in waterfalls where tributary streams enter main valley (Bridalveil Fall in Yosemite)
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- Deep, straight valleys carved by glaciers, often below sea level
- Can become fjords when flooded by seawater after glacial retreat
- Examples include Sognefjord (Norway) and Milford Sound (New Zealand)
Glacial depositional features
- Moraines
- Ridges or mounds of unsorted glacial debris (till) deposited directly by glacier
- Terminal moraines mark farthest extent of glacier advance
- Lateral moraines form along sides of glaciers
- Medial moraines result from merging of two lateral moraines when glaciers converge
- Ground moraines are flat or gently undulating layers of till deposited as glacier retreats
- Eskers
- Long, winding ridges of stratified sand and gravel formed by streams flowing through tunnels beneath or within glaciers
- Can extend for many kilometers and reach heights of 100 meters
- Provide important habitat and travel routes in otherwise flat landscapes
- Drumlins
- Elongated hills composed of glacial till with streamlined shape and blunt end facing direction of ice flow
- Often occur in groups called drumlin fields
- Examples include drumlins in upstate New York and County Down, Ireland
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- Large boulders transported by glaciers and deposited far from their source
- Can be used to trace glacier movement and determine ice flow direction
- Plymouth Rock (Massachusetts) is a famous glacial erratic
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- Formed when buried ice blocks melt, leaving depressions that fill with water
- Often found in outwash plains or end moraine complexes
- Examples include lakes in Minnesota (Land of 10,000 Lakes) and Finland
- Kames
- Irregular mounds of stratified sand and gravel deposited by meltwater at glacier margin
- Often associated with kettles in "kame and kettle" topography
- Provide important aquifers in glaciated regions
Alpine vs continental glacier landforms
- Alpine glacier landforms
- Typically found in mountainous regions at high elevations or latitudes
- Create features like cirques, arêtes, and horns through erosion of mountain peaks
- U-shaped valleys and hanging valleys characterize lower elevations
- Lateral and terminal moraines common at valley mouths
- Continental glacier landforms
- Affect much larger areas, often entire regions or continents
- Create extensive till plains and outwash plains covering vast areas
- Form drumlins, eskers, and kettle lakes across low-relief landscapes
- Produce large end moraines marking former ice sheet boundaries (Great Lakes region)
- Shared features
- Both types create striations and grooves on bedrock indicating ice flow direction
- Erratics (large transported boulders) deposited by both alpine and continental glaciers
- Glacial lakes form in landscapes shaped by either type (proglacial, kettle, finger lakes)
- Scale differences
- Alpine glaciers create localized, dramatic topography in mountain ranges
- Continental glaciers shape entire regions, creating subtle but extensive landforms
- Continental glaciers generally produce larger versions of some alpine glacier features (moraines, outwash plains)
Key Terms to Review (25)
Abrasion: Abrasion is the process of wearing away material from a surface through friction and impact, often caused by the movement of particles. It plays a crucial role in shaping landscapes by removing soil and rock, and contributes to the formation of various geological features over time.
Antarctic Ice Sheet: The Antarctic Ice Sheet is the largest single mass of ice on Earth, covering about 14 million square kilometers, primarily located on the continent of Antarctica. It plays a crucial role in regulating global sea levels and climate patterns and has a significant impact on glacial erosion and depositional features, as well as historical climate changes during glacial periods.
Arêtes: Arêtes are sharp, narrow ridges formed by glacial erosion, typically found in mountainous regions. They occur when two glaciers erode adjacent valleys, creating steep sides that culminate in a sharp ridge. This unique feature is often a dramatic result of the differential erosion that occurs between the glacier's movement and the surrounding landscape.
Basal sliding: Basal sliding is the process by which a glacier moves over its bed due to the melting of ice at the base, allowing the glacier to slide over the underlying substrate. This movement is influenced by factors like pressure, temperature, and the presence of meltwater, which reduces friction and enables glaciers to flow more easily. Understanding basal sliding is crucial because it plays a significant role in glacial dynamics and contributes to erosion and the formation of various landforms.
Cirques: Cirques are bowl-shaped depressions formed by glacial erosion, typically found at the head of a glacier. They are characterized by steep walls and often contain a small lake called a tarn. These features are significant as they showcase the powerful erosional capabilities of glaciers and can provide insight into past climatic conditions, including those during major glaciation events.
Cryosphere: The cryosphere refers to the frozen water part of the Earth's system, which includes glaciers, ice caps, sea ice, and permafrost. This critical component plays a significant role in regulating global climate and sea levels, while also impacting various glacial erosion and depositional features that shape landscapes. Understanding the cryosphere is essential for recognizing its effects on ecosystems, weather patterns, and human activities in polar and alpine regions.
Drumlins: Drumlins are elongated hills or ridges formed by the movement of glacial ice, typically consisting of compacted glacial till. These features are often found in clusters and can provide insights into the direction of ice flow, showcasing the effects of glacial erosion and deposition on the landscape. Understanding drumlins is crucial for studying past glaciations, particularly during the Pleistocene epoch, as they reflect the dynamic relationship between glaciers and the environment.
Erratics: Erratics are large boulders or rock fragments that have been transported from their original location by glacial activity and deposited in an area where the rock type is different from the surrounding geology. These features are significant as they provide clues about past glacial movements, helping to reconstruct ancient ice flow patterns and understand the dynamics of glacial erosion and deposition.
Eskers: Eskers are long, winding ridges of sand and gravel that are formed by the deposition of sediment from meltwater streams flowing beneath a glacier. These features are significant as they reveal the movement and melting patterns of glaciers, providing insight into past glacial activity. The shape and structure of eskers can also offer clues about the hydrological processes occurring during glacial periods.
Glacial striations: Glacial striations are long, thin grooves or scratches that are formed on bedrock by the movement of glaciers as they flow over the surface. These markings provide valuable evidence of past glacial activity and help scientists understand the direction of glacier movement and the history of ice ages.
Glacial Troughs: Glacial troughs are U-shaped valleys formed by the erosional activity of glaciers as they flow through mountainous regions. These troughs are characterized by steep sides and a broad, flat floor, resulting from the glacier's ability to carve out the landscape as it moves, reshaping it significantly. The formation of glacial troughs is closely linked to other glacial features such as cirques, hanging valleys, and fjords, all of which illustrate the power of glacial erosion in sculpting landforms.
Glaciation: Glaciation refers to the process during which large areas of the Earth's surface become covered by glaciers and ice sheets, significantly shaping the landscape and influencing climate. This process has occurred repeatedly throughout Earth's history, marked by periods of extensive ice coverage followed by warmer interglacial periods. Glaciation not only affects landforms and ecosystems but also plays a crucial role in understanding the geologic time scale and past climatic changes.
Glaciology: Glaciology is the scientific study of glaciers and ice sheets, focusing on their formation, movement, and impact on the environment. This field explores how glaciers shape landscapes through processes like erosion and deposition, revealing insights into past climates and future changes in our planet's climate system.
Greenland Ice Sheet: The Greenland Ice Sheet is a massive body of ice covering roughly 1.7 million square kilometers, making it the second-largest ice sheet in the world after Antarctica. It plays a crucial role in understanding glacial processes and climate change, as its melting contributes significantly to global sea-level rise and reflects past climate conditions.
Hanging Valleys: Hanging valleys are elevated valleys that typically occur at the mouths of tributary glaciers, which are higher than the main valley floor formed by a larger glacier. These valleys often present steep cliffs where the tributary glaciers have retreated, leading to picturesque waterfalls as water flows from the hanging valley into the main valley below. They illustrate the erosional processes of glaciers and their impact on landscape formation.
Holocene: The Holocene is the current geological epoch that began approximately 11,700 years ago after the last major ice age, marking a significant period of climate stability and the development of human civilizations. It follows the Pleistocene epoch and is characterized by the warming of the Earth, leading to rising sea levels and the flourishing of flora and fauna, which greatly influenced human settlement and activities.
Horns: Horns are sharp, pyramid-like peaks that form in mountainous regions due to the erosion caused by glaciers. They are typically formed when multiple glaciers carve away at a mountain, leading to the creation of steep ridges and pointed summits. Horns are a striking feature of glacial landscapes, often standing out prominently against surrounding topography and showcasing the power of glacial erosion.
Ice flow: Ice flow refers to the movement of glacier ice, driven primarily by gravity and influenced by the physical properties of the ice and underlying terrain. This movement plays a crucial role in shaping the landscape through processes such as glacial erosion and deposition, leading to the formation of various landforms like moraines and drumlins.
Kames: Kames are irregularly shaped hills or mounds formed by glacial deposition, specifically by the accumulation of sand and gravel. They typically occur in regions once covered by glaciers and are the result of meltwater streams depositing sediment as the glacier retreats. Kames are an important feature of the glacial landscape, often found alongside other glacial formations such as eskers and moraines, and they play a key role in understanding past glacial activity and sediment transport processes.
Kettle lakes: Kettle lakes are depressions or basins formed by the melting of glacial ice, which leaves behind blocks of ice that eventually melt and create a lake. These features are commonly associated with glacial environments and are significant indicators of past glacial activity, illustrating the processes of glacial erosion and deposition. Kettle lakes can vary in size and depth and often provide unique ecosystems and habitats for various flora and fauna.
Moraines: Moraines are accumulations of debris, such as soil and rock, that are transported and deposited by glaciers. They serve as important indicators of past glacial activity and play a key role in understanding the processes of glacial erosion and deposition. These landforms can vary in size and shape, providing insights into the dynamics of glacier movement and the climate conditions that influenced their formation.
Periglacial Processes: Periglacial processes refer to the geomorphological and climatic phenomena that occur in areas adjacent to glaciers and ice sheets, characterized by conditions just below freezing. These processes influence landforms and sediment transport in cold environments, often leading to features like patterned ground, frost action, and solifluction. Understanding periglacial processes helps to elucidate how landscapes evolve in response to freeze-thaw cycles and other climate-related factors.
Pleistocene: The Pleistocene is a geological epoch that lasted from about 2.6 million years ago to approximately 11,700 years ago, characterized by repeated glaciations and significant changes in climate and sea levels. This period saw the development of major ice sheets in the Northern Hemisphere and is marked by the emergence and evolution of various species, including early humans. The Pleistocene's glacial and interglacial cycles shaped much of today's landscape and influenced ecological patterns.
Plucking: Plucking is a glacial erosion process where a glacier picks up and removes rocks and sediment from the landscape as it moves. This occurs when the pressure of the ice causes it to melt at the base, allowing the glacier to grasp the underlying materials, which are then transported along with the ice. This process plays a crucial role in shaping landforms and is fundamental in understanding glacial erosion and depositional features.
U-shaped valleys: U-shaped valleys are elongated, trough-like landforms created by the erosive action of glaciers. These valleys are characterized by their steep sides and flat bottoms, which contrast with the V-shaped profiles of river valleys. They often serve as indicators of past glacial activity and play a significant role in understanding the dynamics of glacial erosion and landscape evolution.