3.4 Glaciers and Ice Ages
7 min read•august 14, 2024
Glaciers, massive bodies of ice that persist year-round, shape Earth's surface through erosion and deposition. From alpine glaciers in mountains to continental ice sheets, these icy giants carve landscapes and leave behind distinctive landforms, influencing our planet's geography.
Ice ages, driven by orbital variations and changes in atmospheric composition, have profound effects on Earth's climate and ecosystems. By studying past glacial periods, scientists gain insights into Earth's climate system, helping us understand and predict future climate change.
Glaciers and their types
Types of glaciers
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- Alpine glaciers are found in mountainous regions and include:
- glaciers, which form in bowl-shaped depressions on mountainsides
- Valley glaciers, which flow down pre-existing river valleys
- Piedmont glaciers, which form when valley glaciers spill out onto flatter plains at the base of mountains
- Continental glaciers, also known as ice sheets, are much larger than alpine glaciers and can cover vast areas of land
- Examples include the present-day ice sheets in Antarctica and Greenland, which cover entire continents
Characteristics and formation of glaciers
- Glaciers are massive bodies of ice that persist year-round and flow under their own weight due to gravity
- forms from the accumulation and compaction of snow over many years
- As snow accumulates, it compresses the underlying layers, transforming them into dense, crystalline ice
- Glaciers move downslope or outward from their source region due to gravity and the pressure of the overlying ice
- The movement of glaciers is slow, typically ranging from a few centimeters to a few meters per day
- The speed of glacial movement depends on factors such as the thickness of the ice, the steepness of the slope, and the temperature of the ice
Glacial erosion and deposition
Processes of glacial erosion
- involves the glacier freezing onto bedrock and removing large chunks of rock as it moves downslope
- Water seeps into cracks in the bedrock and freezes, expanding and loosening the rock
- As the glacier moves, it plucks out the loosened rock fragments, leaving behind jagged, irregular surfaces
- occurs when rocks and debris embedded in the base of the glacier scrape and polish the bedrock beneath
- The embedded rocks act like sandpaper, creating smooth surfaces and parallel scratches called striations
- Glacial abrasion can also produce grooves, chattermarks, and polished surfaces on the bedrock
- happens when water seeps into cracks in the bedrock, freezes, and expands, causing the rock to break apart
- This process is also known as or
- Repeated cycles of freezing and thawing can significantly weaken and fragment the bedrock, making it more susceptible to erosion
Glacial deposition and landforms
- occurs when the glacier melts and releases the sediment it has been carrying, creating various landforms
- The size and shape of the deposited sediment depend on factors such as the glacier's velocity, the amount of meltwater, and the underlying topography
- are ridges of glacially deposited sediment, classified based on their location relative to the glacier
- Lateral moraines form along the sides of the glacier, while medial moraines form where two glaciers merge
- Terminal moraines are deposited at the end of the glacier, marking its maximum extent
- Drumlins are elongated, teardrop-shaped hills composed of (unsorted sediment)
- They are formed beneath the glacier and are aligned with the direction of ice flow
- Drumlins can range in size from a few meters to several kilometers in length
- Eskers are long, winding ridges of sand and gravel deposited by meltwater streams flowing beneath or within the glacier
- They can extend for several kilometers and are often used as natural roadbeds in glaciated regions
Landforms of glacial activity
Erosional landforms
- Cirques are bowl-shaped depressions carved into mountainsides by the erosive action of glaciers
- They often feature a steep headwall and a flat or overdeepened floor, where a small lake (tarn) may form after the glacier has melted
- Cirques are the starting points for alpine glaciers and can enlarge over time through continued
- Arêtes are sharp, narrow ridges formed when two cirques erode back-to-back
- They are characterized by steep, knife-like edges and can be challenging to traverse
- Examples of arêtes include the Matterhorn in the Alps and the Garden Wall in Glacier National Park, Montana
- Horns are steep, pyramid-shaped peaks resulting from the erosion of multiple cirques
- They form when three or more cirques erode the sides of a mountain, leaving a distinctive pointed peak
- The Matterhorn in the Alps is a classic example of a glacial
- U-shaped valleys are created by the erosive power of valley glaciers, which widen and deepen pre-existing river valleys
- They are characterized by steep, parallel walls and a flat, wide floor, in contrast to the V-shaped profiles of river-carved valleys
- Yosemite Valley in California is a well-known example of a U-shaped glacial valley
- Hanging valleys are tributary valleys left "hanging" above the main glacial valley due to the more rapid erosion of the main glacier
- They often feature waterfalls, as the tributary streams cascade down to meet the main valley floor
- Bridal Veil Falls in Yosemite National Park is an example of a waterfall formed by a
Depositional landforms
- Moraines are ridges of glacially deposited sediment, classified as lateral, medial, or terminal based on their location relative to the glacier
- Lateral moraines form along the sides of the glacier, while medial moraines form where two glaciers merge
- Terminal moraines are deposited at the end of the glacier, marking its maximum extent
- The Outer Lands of Cape Cod, Massachusetts, are an example of a complex
- Drumlins are elongated, teardrop-shaped hills composed of glacial , formed beneath the glacier and aligned with the direction of ice flow
- They can range in size from a few meters to several kilometers in length
- The Field in Wisconsin is a well-known example, featuring thousands of drumlins formed during the last ice age
- Eskers are long, winding ridges of sand and gravel deposited by meltwater streams flowing beneath or within the glacier
- They can extend for several kilometers and are often used as natural roadbeds in glaciated regions
- The Denali Highway in Alaska follows the path of a large formed by glacial meltwater
Causes and effects of ice ages
Causes of ice ages
- Variations in Earth's orbit () are a primary driver of ice ages
- refers to the shape of Earth's orbit, which varies from nearly circular to more elliptical over a 100,000-year cycle
- is the tilt of Earth's axis, which varies between 22.1° and 24.5° over a 41,000-year cycle
- is the wobble of Earth's axis, which affects the timing of seasons over a 26,000-year cycle
- Changes in atmospheric composition, particularly reduced greenhouse gas concentrations, can contribute to cooling and the onset of ice ages
- Lower levels of carbon dioxide and methane in the atmosphere allow more heat to escape Earth's surface, leading to global cooling
- Variations in solar output, such as decreased solar activity during the Maunder Minimum (1645-1715), can also influence Earth's climate and potentially contribute to cooling
Effects of ice ages
- During glacial periods, sea levels drop due to water being locked up in ice sheets, exposing land bridges and altering global ocean circulation patterns
- The Bering Land Bridge, which connected Asia and North America during the last ice age, allowed for the migration of humans and other species between the continents
- Ice ages have significant effects on Earth's climate, ecosystems, and biodiversity
- Colder temperatures and reduced precipitation during glacial periods lead to the expansion of grasslands and tundra biomes, while forests contract
- Many species adapt to the changing conditions through evolutionary processes, while others may face extinction due to habitat loss or competition
- Positive feedback mechanisms, such as the ice-albedo feedback, can amplify the cooling effect during an ice age
- As ice sheets expand, they reflect more of the sun's energy back into space (higher albedo), further cooling the planet
- This feedback loop can intensify and prolong the cooling trend, until other factors (e.g., increasing greenhouse gases) eventually offset the cooling and lead to warming
Studying past ice ages
- The , which began about 2.6 million years ago and ended 11,700 years ago, is characterized by multiple glacial-interglacial cycles
- During this time, Earth experienced several major glacial periods, interspersed with warmer interglacial periods
- The most recent glacial period, known as the , occurred about 26,500 to 19,000 years ago
- Scientists study past ice ages using a variety of methods, including:
- Analysis of ice cores, which provide a record of past atmospheric composition and temperature
- Examination of glacial landforms and sediments, which offer insights into the extent and dynamics of past glaciations
- Study of fossil records, which reveal how ecosystems and species responded to changing climate conditions
- Understanding past ice ages helps scientists better comprehend Earth's climate system and predict future climate change
- By studying the causes, effects, and cyclical nature of past glaciations, researchers can improve climate models and anticipate the potential impacts of current and future climate change on our planet
Key Terms to Review (40)
Abrasion: Abrasion is the process of wearing away material through friction and impact, primarily caused by natural forces such as water, wind, and ice. This action leads to the smoothing and shaping of various surfaces and landscapes, contributing to the formation of distinct landforms over time. Abrasion plays a crucial role in shaping geological features, influencing sediment transport, and modifying environments across various ecosystems.
Alpine Glacier: An alpine glacier is a type of glacier that forms in mountainous regions, typically confined within a valley or cirque. These glaciers flow down from higher elevations, sculpting the landscape and contributing to various geological processes. They are key indicators of climate change and play a significant role in understanding past glacial periods during ice ages.
Arête: An arête is a sharp, narrow ridge of rock that forms between two valleys or glacial troughs, typically found in mountainous regions shaped by glacial erosion. These formations result from the process where glaciers carve out the surrounding landscape, leading to the steep, jagged edges characteristic of an arête. They are often prominent features in alpine terrains and can be quite dramatic in appearance, serving as a testament to the powerful forces of ice and rock in shaping Earth’s surface.
Cirque: A cirque is a bowl-shaped depression formed by glacial erosion, typically found at the head of a glacier. It is characterized by steep, often rocky walls and a flat bottom, where the ice has sculpted the landscape over time. Cirques serve as important indicators of past glacial activity and are often associated with other glacial features such as aretes and tarns.
Cirque glacier: A cirque glacier is a type of glacier that forms in a bowl-shaped depression on the side of a mountain, known as a cirque. These glaciers are often the result of snow accumulation and compaction in these depressions, which leads to the movement of ice down the slope due to gravity. Cirque glaciers are crucial indicators of climate change and glacial processes, playing a significant role in shaping mountain landscapes.
Climate Oscillation: Climate oscillation refers to periodic fluctuations in climate patterns that can affect global temperatures, precipitation, and atmospheric conditions over various timescales. These oscillations can influence ice ages, glacial periods, and interglacial periods, playing a significant role in shaping Earth’s climate history.
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 mountain ranges. These glaciers can extend over thousands of square kilometers and play a significant role in shaping the Earth's landscape through processes like erosion and sediment deposition. They are distinct from alpine glaciers, which form in mountainous areas and flow down valleys.
Drumlin: A drumlin is a streamlined, elongated hill formed by the movement of glacial ice. These landforms are typically composed of glacial till and are oriented in the direction of ice flow, often found in clusters known as drumlin fields. Understanding drumlins helps in recognizing past glacial activity and the dynamics of ice sheets during ice ages.
Eccentricity: Eccentricity is a measure of how much an orbit deviates from being circular, quantified by a value ranging from 0 to 1. In the context of Earth's orbit around the Sun, it plays a crucial role in understanding the variations in solar radiation received by the planet, which can influence climatic patterns and the advancement or retreat of glaciers during ice ages.
Esker: An esker is a long, winding ridge of stratified sand and gravel that forms from sediment deposited by meltwater streams flowing beneath a glacier. These features are remnants of glacial activity and provide important insights into past ice movement and landscape evolution, illustrating how glaciers shape the earth's surface during periods of glaciation.
Freeze-thaw action: Freeze-thaw action is a geological process where water infiltrates cracks in rocks, freezes, and expands, causing the rock to fracture further. This repeated cycle of freezing and thawing weakens the rock structure over time, contributing to physical weathering and erosion, especially in environments affected by glaciers and ice ages.
Frost Wedging: Frost wedging is a geological process where water seeps into cracks in rocks, and upon freezing, expands to exert pressure on the surrounding rock, leading to the fragmentation of the rock. This natural phenomenon is significant in the context of weathering, erosion, and landscape formation, particularly in cold climates where freezing and thawing cycles are frequent. Frost wedging plays a crucial role in breaking down larger rock masses into smaller pieces, which can then be transported by glaciers and contribute to the shaping of landforms during ice ages.
Glacial Deposition: Glacial deposition refers to the process by which glaciers leave behind sediment and landforms as they advance and retreat. This occurs when glaciers melt or calve, releasing material such as rocks, dirt, and other debris that were carried along in the ice. The resulting deposits can create distinct landforms and landscapes, showcasing the dynamic nature of glacial activity and its impact on the Earth's surface.
Glacial Erosion: Glacial erosion is the process by which glaciers wear away and sculpt the land as they move. This occurs through mechanisms like abrasion, where rocks and sediments trapped within the ice scrape against the bedrock, and plucking, where ice pulls away pieces of rock as it advances. The resulting landforms provide insights into past climate conditions and the powerful forces shaping Earth's surface.
Glacial Ice: Glacial ice is the dense, compacted form of ice that forms from the accumulation and compaction of snow over long periods, resulting in a solid mass that flows under the influence of gravity. This unique ice is essential for the formation of glaciers and plays a significant role in Earth's climate and hydrological systems. As glaciers move and shape landscapes, glacial ice serves as an indicator of climate change, with its mass and extent reflecting environmental conditions.
Glacial landform: Glacial landforms are natural features created by the movement and erosion of glaciers over time. These landforms include a variety of shapes and structures, such as valleys, moraines, and cirques, which reveal the powerful impact glaciers have on the landscape during periods of glaciation. Understanding glacial landforms is essential for comprehending how ice ages have shaped Earth's topography and influenced ecosystems.
Glacial Retreat: Glacial retreat refers to the process where glaciers lose mass and recede in response to changes in climate, specifically increasing temperatures. This phenomenon is a clear indicator of climate change and reflects the balance between accumulation of snow and ice and melting processes. As temperatures rise, glaciers melt faster than they can replenish, leading to significant impacts on landscapes, sea levels, and ecosystems.
Glacial Till: Glacial till is the unsorted and unstratified sediment deposited directly by a glacier as it advances and retreats. This material, which includes a mixture of clay, silt, sand, gravel, and boulders, showcases the diverse geological history shaped by glacial movements during ice ages. The unique composition of glacial till can provide important insights into past climate conditions and the processes that shaped the Earth's surface.
Gps monitoring: GPS monitoring refers to the use of Global Positioning System technology to track and analyze the movement and location of objects or phenomena over time. This technology allows scientists to gather precise data on glaciers, including their movement, melting rates, and changes in mass, providing crucial insights into climate change and its effects on Earth’s cryosphere.
Hanging Valley: A hanging valley is a geological formation that occurs when a smaller valley cuts into a larger valley, typically formed by glacial erosion. This results in a valley that is elevated above the main valley floor, often featuring steep cliffs and sometimes waterfalls where streams flow from the hanging valley down to the main valley. These valleys showcase the powerful effects of glacial activity during ice ages, illustrating how glaciers carve out landscapes in distinctive ways.
Horn: In the context of glaciers and ice ages, a horn is a sharp, pyramid-shaped peak that is formed when multiple glaciers erode a mountain from several sides. This intense erosion creates a pointed summit, often surrounded by steep ridges. Horns are a striking feature of glacial landscapes and serve as indicators of past glacial activity.
Ice Age Theory: Ice Age Theory refers to the scientific understanding of the periods in Earth's history when large parts of the planet were covered by glaciers and ice sheets, significantly altering climate, sea levels, and ecosystems. This theory explains the causes and consequences of these glacial periods, including factors such as changes in Earth's orbit, volcanic activity, and variations in solar radiation. Understanding this theory is crucial for grasping how glaciers shape landscapes and influence climate patterns over geological time scales.
Ice core sampling: Ice core sampling is a scientific technique used to extract long cylindrical sections of ice from glaciers and ice sheets, allowing researchers to analyze past climate conditions and atmospheric compositions. This method reveals valuable information about Earth's climate history, including temperature fluctuations and greenhouse gas levels, by preserving air bubbles and particulates trapped in the ice layers over thousands of years.
Ice wedging: Ice wedging is a physical weathering process where water seeps into cracks in rocks, freezes, and expands, causing the rock to break apart. This process is crucial in shaping landscapes, especially in colder climates where repeated freeze-thaw cycles occur, leading to significant geological changes over time.
Last glacial maximum: The last glacial maximum (LGM) refers to the period during the last Ice Age when ice sheets reached their greatest extent, approximately 26,500 years ago. This time was characterized by significantly lower global temperatures and widespread glaciation, profoundly impacting Earth's climate, ecosystems, and human populations. The LGM was a critical point in Earth's history, influencing the distribution of flora and fauna as well as human migration patterns.
Lateral moraine: A lateral moraine is a ridge of debris deposited alongside a glacier, formed from the accumulation of rock, soil, and other material that has been eroded from the valley walls. These features are significant in understanding glacier movement and the processes that shape mountainous landscapes. Lateral moraines can provide insights into past glacial activity and are often used as indicators of the glacier's extent at various times during its advance and retreat.
Medial moraine: A medial moraine is a ridge of debris that forms in the middle of a glacier, created when two glaciers merge and their lateral moraines combine. This feature indicates the path of glacial movement and showcases the accumulation of sediment transported by the ice. Medial moraines are important for understanding glacier dynamics and landscape evolution during ice ages.
Milankovitch Cycles: Milankovitch cycles are long-term variations in Earth's orbit and axial tilt that affect climate patterns over thousands of years. These cycles, driven by gravitational interactions with other celestial bodies, play a crucial role in the timing and intensity of ice ages, influencing the advance and retreat of glaciers across the planet.
Moraines: Moraines are accumulations of debris and sediment that are deposited by glaciers as they advance and retreat. These formations are key indicators of glacial activity, often taking the shape of ridges or mounds that reflect the glacier's movement. Understanding moraines helps to reveal the history of ice ages, climate change, and landscape evolution over time.
Obliquity: Obliquity refers to the angle of tilt of a planet's rotational axis relative to its orbital plane around the sun. For Earth, this angle varies over time between approximately 22.1 degrees and 24.5 degrees due to gravitational interactions with other celestial bodies. This axial tilt influences climate patterns, particularly in relation to the formation and melting of glaciers, making it a crucial factor in understanding ice ages and glacial cycles.
Outwash: Outwash refers to sediment that has been transported away from a glacier by meltwater. This process occurs as glaciers retreat and melt, allowing streams of water to carry away materials such as sand, silt, and gravel, which are deposited in layered formations known as outwash plains. The characteristics of outwash deposits are crucial for understanding past glacial activity and the shaping of landscapes during ice ages.
Piedmont Glacier: A piedmont glacier is a type of glacier that forms when a valley glacier spills out of its valley and spreads out onto a lowland area, typically where it meets a larger body of water or an open plain. This unique formation occurs as the glacier's flow is no longer constrained by valley walls, allowing it to expand laterally and cover a broader area, creating distinctive landforms such as lobes and ridges. Piedmont glaciers are significant as they provide insights into glacial dynamics and the interactions between ice and the surrounding environment.
Pleistocene Epoch: The Pleistocene Epoch is a geological period that lasted from about 2.6 million to 11,700 years ago, characterized by repeated glaciations and significant climate changes. It played a crucial role in shaping the Earth's landscape and ecosystems, as massive ice sheets expanded and retreated, influencing sea levels and the distribution of flora and fauna.
Plucking: Plucking is the geological process where glaciers erode the underlying bedrock by freezing onto it and then pulling it away as they move. This process significantly contributes to the shaping of landscapes, creating features such as U-shaped valleys and jagged mountain peaks, which are characteristic of glacial regions. As glaciers advance, they can carry large volumes of rock debris, transforming both the glacier itself and the land it traverses.
Precession: Precession is the gradual shift in the orientation of an astronomical body's rotational axis, primarily influenced by gravitational forces exerted by other celestial bodies. This phenomenon plays a crucial role in long-term climate patterns, particularly affecting the Earth's climate by altering the distribution of sunlight on the planet, which can lead to ice ages and interglacial periods.
Sea level rise: Sea level rise refers to the increasing height of the ocean's surface, primarily caused by two main factors: the melting of glaciers and polar ice, and the thermal expansion of seawater as it warms. This phenomenon has significant implications for coastal regions, marine ecosystems, and global climate patterns, affecting everything from habitat loss to increased flooding in vulnerable areas.
Terminal moraine: A terminal moraine is a pile of debris, primarily composed of rocks and sediments, that accumulates at the furthest point of a glacier's advance. This geological feature marks the maximum extent of glacial movement and is formed as glaciers push and deposit material from the land they traverse. Terminal moraines provide crucial evidence of past glacial activity and can help scientists understand the dynamics of glacial movement during ice ages.
Till: Till is a type of unsorted glacial sediment that is deposited directly by glacial ice as it melts. This material is composed of a mix of clay, silt, sand, and larger rock fragments, and it provides important evidence of past glacial activity. The characteristics of till help scientists understand the processes and movements of glaciers during ice ages, revealing how glaciers shaped the landscape and contributed to soil formation in various regions.
U-Shaped Valley: A U-shaped valley is a distinctive landform characterized by its broad, flat floor and steep, glacially carved sides, resembling the letter 'U'. These valleys are typically formed by the erosion caused by moving glaciers, which carve out the landscape as they advance and retreat. The U-shape is a result of the powerful grinding action of ice against the valley walls and floor, creating a smooth, wide-bottomed profile that differentiates it from V-shaped valleys created by river erosion.
Valley glacier: A valley glacier is a type of glacier that flows down a mountain valley, often originating from an ice field or a larger ice mass. These glaciers are typically confined to the valley walls and are shaped by the landscape, carving out U-shaped valleys as they advance. Their movement and melting can significantly influence the surrounding environment and contribute to the processes of erosion and sediment transport.