7.4 Pleistocene glaciations and their impact on landscapes
5 min read•july 30, 2024
Pleistocene glaciations reshaped Earth's surface, leaving lasting marks on landscapes worldwide. Massive ice sheets advanced and retreated multiple times, driven by and climate feedbacks, carving valleys, depositing sediments, and altering sea levels.
These glacial cycles profoundly impacted global climate and ecosystems. The resulting landforms, from U-shaped valleys to drumlins and moraines, continue to influence modern topography, hydrology, and ecology, shaping the world we inhabit today.
Pleistocene Glaciations: Causes and Extent
Milankovitch Cycles and Climate Feedback
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- spanned from approximately 2.6 million to 11,700 years ago characterized by multiple
- Milankovitch cycles drove these climate fluctuations through variations in Earth's orbital parameters
- Orbital eccentricity changes Earth's distance from the sun over a 100,000-year cycle
- Axial tilt varies between 22.1° and 24.5° over a 41,000-year cycle affecting seasonal contrasts
- Precession alters the orientation of Earth's axis over a 26,000-year cycle influencing which hemisphere faces the sun at perihelion
- mechanisms amplified orbital forcing effects
- Atmospheric CO2 concentrations decreased during glacial periods (180 ppm) and increased during interglacials (280 ppm)
- Albedo effects from expanded reflected more solar radiation reinforcing cooling trends
Glacial-Interglacial Cycles and Global Ice Extent
- occurred around 26,500 to 19,000 years ago marking peak ice sheet extent
- Glacial-interglacial cycles typically lasted about 100,000 years
- Interglacial periods were shorter lasting approximately 10,000-30,000 years
- Pleistocene glaciations affected both hemispheres globally
- North America ice sheets covered much of Canada and northern United States (Laurentide and Cordilleran ice sheets)
- European ice sheets extended over Scandinavia and parts of the British Isles ()
- Asian ice sheets covered parts of Siberia and the Tibetan Plateau
- expanded to the edge of the continental shelf
- Mountain glaciers grew worldwide (Alps, Andes, Himalayas)
Ice Sheets and Their Influence
Major Pleistocene Ice Sheets
- dominated North America
- Covered much of Canada and northern United States
- Reached maximum thickness of about 3-4 km
- Extended as far south as New York and the Ohio River Valley
- Fennoscandian Ice Sheet covered northern Europe
- Spread over Scandinavia and parts of the British Isles
- Attained maximum thickness of about 3 km
- Reached as far south as Germany and Poland
- Antarctic Ice Sheet expanded during glacial periods
- Extended to the edge of the continental shelf
- Increased in volume by approximately 50%
- Merged with expanded sea ice creating a larger ice-covered area
Impacts on Sea Level and Climate
- Global sea levels fluctuated by approximately 120-130 meters between glacial and interglacial periods
- Water transferred between ice sheets and oceans
- Exposed continental shelves during glacial lowstands (Beringia land bridge)
- Ice sheets caused significant isostatic depression of Earth's crust
- Post-glacial rebound continues to affect landscapes today (Hudson Bay rising at 1 cm/year)
- Ice sheets influenced global atmospheric circulation patterns
- Created high-pressure systems over their surfaces altering wind patterns
- Shifted jet stream positions affecting regional climates worldwide
- Strengthened temperature gradients between equator and poles
- of extensive ice cover contributed to global cooling
- Created positive feedback loop reinforcing glacial conditions
- Reflected up to 90% of incoming solar radiation compared to 10-20% for ice-free land
Pleistocene Landforms and Features
Ice-Marginal and Depositional Landforms
- Terminal moraines mark maximum ice sheet extent
- Long Island formed by of Laurentide Ice Sheet
- Recessional moraines indicate pauses or minor advances during overall ice retreat
- Kettle in Wisconsin formed by multiple ice lobes
- Drumlins reveal ice flow direction
- Streamlined hills composed of
- Often found in fields or swarms (Thousand Islands region of New York)
- represent paths of subglacial meltwater channels
- Sinuous ridges of
- Can extend for hundreds of kilometers (Thelon Esker in Canada)
- forms in ice-marginal areas
- Kettles lakes develop in depressions left by melting ice blocks
- Kames are mounds of deposited by meltwater
Proglacial and Erosional Features
- Proglacial lakes formed along ice margins
- Glacial Lake Agassiz in North America covered over 440,000 km²
- Often drained catastrophically as ice retreated (Missoula Floods)
- Glacial erratics trace ice flow paths
- Large boulders transported by ice used to determine provenance
- Plymouth Rock in Massachusetts is a famous
- U-shaped valleys characteristic of alpine glaciation
- Yosemite Valley in California sculpted by Pleistocene glaciers
- Fjords formed by glacial erosion of coastal valleys
- Sognefjord in Norway extends over 200 km inland
- Cirques developed at the heads of alpine glaciers
- Tuckerman Ravine on Mount Washington in New Hampshire
Long-Term Impact of Glaciations
Landscape and Hydrological Changes
- Glacial deposits and landforms continue to influence modern topography
- Drumlins affect local drainage patterns and soil distributions
- Eskers serve as important aquifers in formerly glaciated regions
- causes differential uplift of formerly glaciated areas
- Affects coastlines creating raised beaches (Gulf of Bothnia)
- Tilts lake basins altering drainage patterns (Great Lakes)
- Pleistocene glaciations significantly altered river systems
- Created misfit streams flowing in oversized valleys
- Changed drainage patterns forming new watersheds
- Formed large-scale features like the Great Lakes basin
Geological and Ecological Impacts
- Distribution of glacial features informs reconstructions
- Extent of moraines and erratics map former ice sheet boundaries
- from proglacial lakes record climate fluctuations
- Glacial sediments form important aquifers
- Ogallala Aquifer in central US partly composed of glacial outwash
- Erosion and deposition created economically important resources
- Sand and gravel deposits mined for construction materials
- Glacial till provides fertile soils for agriculture (American Midwest)
- Pleistocene glaciations influenced modern biogeography
- Created refugia for species during glacial periods (Driftless Area in Wisconsin)
- Facilitated species migrations across exposed land bridges
- Shaped distribution of flora and fauna in post-glacial landscapes
- Led to development of unique ecosystems (Great Lakes coastal wetlands)
Key Terms to Review (32)
Albedo effect: The albedo effect refers to the measure of reflectivity of a surface, specifically how much sunlight is reflected back into space without being absorbed. Surfaces with high albedo, like ice and snow, reflect most of the sunlight, while darker surfaces, like oceans or forests, absorb more heat. This concept is critical in understanding climate dynamics, especially in relation to glaciation and periglacial systems.
Antarctic ice sheet: The Antarctic ice sheet is a vast expanse of ice covering the continent of Antarctica, comprising the largest single mass of ice on Earth. This massive ice sheet plays a crucial role in regulating global sea levels and climate, particularly during periods of glaciation, such as the Pleistocene epoch, impacting landscapes through processes like erosion and sediment deposition as it advances and retreats.
Cirque: A cirque is a bowl-shaped, amphitheater-like depression formed by glacial erosion at the head of a glacier. These unique landforms are typically characterized by steep, rocky walls and are often filled with a lake or snow. Cirques are significant because they serve as important indicators of past glacial activity and help illustrate the powerful processes of glacial erosion and landscape transformation.
Climate feedback: Climate feedback refers to processes that can amplify or diminish the effects of climate changes, particularly in relation to temperature. These feedback loops are crucial in understanding how different components of the Earth's system interact and influence one another, ultimately affecting global climate dynamics. During periods like the Pleistocene glaciations, various feedback mechanisms played significant roles in shaping both the extent of ice cover and the resulting alterations in landscapes.
Cordilleran ice sheet: The cordilleran ice sheet was a significant glacial formation during the Pleistocene epoch that covered much of the western region of North America, including parts of Canada and the northern United States. This massive ice sheet played a crucial role in shaping the landscape, influencing geological features, hydrology, and ecosystems across the region as it advanced and retreated during glacial cycles.
Drumlin: A drumlin is a streamlined, elongated hill formed by glacial deposits, typically composed of till, that occurs in a landscape shaped by past glacial activity. These features are often found in groups, indicating the direction of glacial movement and serving as important indicators of the dynamics of ice sheets and the sedimentary processes involved in glacial environments.
Eskers: Eskers are long, winding ridges of stratified sand and gravel that form beneath glaciers, primarily during the melting phase of a glacial period. These features are the result of sediment deposition by meltwater streams flowing through tunnels within the ice, leading to distinctive landforms that can stretch for several kilometers. The study of eskers provides insight into past glacial movements and the hydrological processes associated with Pleistocene glaciations.
Fennoscandian Ice Sheet: The Fennoscandian Ice Sheet was a massive ice sheet that covered much of northern Europe, particularly present-day Finland, Sweden, Norway, and parts of northwest Russia during the last glacial period, known as the Weichselian glaciation. It played a crucial role in shaping the landscapes of the region through processes such as erosion, deposition, and the creation of distinct geological features.
Fjord: A fjord is a long, deep, narrow inlet of the sea between high cliffs or steep slopes, typically formed by the submergence of a glaciated valley. Fjords are often characterized by their unique geological formations and the processes that shape them, including glacial erosion and sea-level changes. These striking features provide insight into the interactions between land and water, and the impact of glacial movements on landscapes over time.
Glacial erratic: A glacial erratic is a boulder or large rock that has been transported and deposited by a glacier, often found far from its source location. These erratics can vary in size and composition and are crucial for understanding the movement of glaciers and their impact on the landscape. By studying glacial erratics, scientists can gain insights into past glaciation events and how they shaped the terrain we see today.
Glacial till: Glacial till is unsorted and unstratified sediment deposited directly by a glacier as it advances or retreats. This type of sediment consists of a mix of rock fragments, clay, silt, sand, and boulders, varying greatly in size and composition. The presence of glacial till provides important clues about past glacial movements and the conditions under which they formed.
Glacial-interglacial cycles: Glacial-interglacial cycles refer to the natural fluctuations in Earth's climate that lead to periods of glacial expansion and retreat, significantly influencing global temperatures and sea levels. These cycles are driven by factors such as changes in Earth's orbit, solar radiation, and greenhouse gas concentrations, which play a crucial role in shaping landscapes and ecosystems over thousands of years.
Glaciofluvial sediment: Glaciofluvial sediment refers to materials transported and deposited by meltwater from glaciers. These sediments are typically a mix of various particle sizes, ranging from fine silt to large boulders, shaped by the glacial processes of erosion and transportation. The deposition of glaciofluvial sediment plays a crucial role in shaping landforms and influencing hydrology in areas previously covered by ice during past glaciations.
Ice cover: Ice cover refers to the area of the Earth's surface that is covered by ice, including glaciers, ice caps, and sea ice. This term is crucial for understanding how Pleistocene glaciations shaped landscapes, as extensive ice cover during this period influenced erosion, deposition, and the formation of various landforms.
Interglacial period: An interglacial period is a warm phase that occurs between glacial periods, characterized by a significant reduction in ice coverage on Earth. During these times, global temperatures rise, leading to changes in ecosystems, sea levels, and atmospheric conditions. Interglacial periods are crucial for understanding past climate patterns and the resulting impacts on landscapes and biodiversity.
Isostatic Rebound: Isostatic rebound refers to the process where the Earth's crust rises after being compressed by the weight of ice sheets or other heavy loads. This adjustment occurs after the melting of ice or the removal of weight, allowing the crust to gradually regain its equilibrium. This phenomenon is crucial in understanding landscape changes and geological processes following glaciations, erosion, and shifts in sea levels.
Kame and kettle topography: Kame and kettle topography is a distinctive landform created by the melting of glacial ice, resulting in a landscape characterized by irregular hills (kames) and depressions (kettles). This type of topography develops as sediment accumulates around glacial features, and when the ice melts, it leaves behind these mounds and pits that can vary widely in size and shape. These landforms are significant as they illustrate the dynamic processes of glaciation and its impact on shaping the Earth's surface.
Kettle lake: A kettle lake is a body of water that forms in depressions left behind by melting glaciers. These lakes are typically round or oval-shaped and can vary greatly in size. They play an important role in shaping local ecosystems, as they often provide habitats for various plant and animal species, while also influencing groundwater recharge and surface water dynamics.
Last glacial maximum: The last glacial maximum (LGM) refers to the most recent period during the last Ice Age when ice sheets were at their greatest extent, occurring around 26,500 years ago. This event significantly influenced global climate patterns, sea levels, and landscapes, leaving lasting impacts on the Earth’s surface processes and environments that are still observable today.
Laurentide Ice Sheet: The Laurentide Ice Sheet was a massive ice sheet that covered a significant portion of North America during the last glacial maximum of the Pleistocene Epoch, approximately 26,000 years ago. This ice sheet played a crucial role in shaping the landscapes of Canada and parts of the northern United States through processes like erosion, sediment deposition, and glacial landform creation.
Milankovitch cycles: Milankovitch cycles refer to the long-term variations in the Earth's orbit and axial tilt that influence climate patterns over thousands of years. These cycles are driven by changes in the Earth's eccentricity, axial tilt, and precession, which collectively affect the distribution and intensity of sunlight received by the Earth, playing a critical role in the timing and intensity of glacial and interglacial periods during the Pleistocene.
Moraine: A moraine is a landform created from the accumulation of debris, primarily composed of rocks and sediments, that has been transported and deposited by glaciers. Moraines serve as important indicators of past glacial activity and are essential in understanding how glaciers interact with the landscape, shaping it through both erosion and deposition processes.
Outwash plain: An outwash plain is a flat, sediment-rich area formed by the deposition of materials transported by meltwater from glaciers. These plains are characterized by layers of sand and gravel that have been washed out from the glacier and spread out over the surrounding landscape. The outwash plain is an important landform that showcases the processes of glacial deposition, playing a significant role in shaping the environment during and after glaciation events.
Paleoclimate: Paleoclimate refers to the climate conditions of the Earth during previous geological eras, determined through various forms of evidence such as ice cores, sediment layers, and fossil records. Understanding paleoclimate helps scientists to reconstruct past environments and climate changes, providing insights into how Earth's climate system operates and responds to natural processes over time.
Paleoecology: Paleoecology is the study of ancient ecosystems and the interactions between organisms and their environments over geological time. This field helps us understand how past climates, landscapes, and living organisms have changed and influenced each other, particularly in relation to significant events like glaciations.
Pleistocene Epoch: The Pleistocene Epoch, lasting from about 2.6 million to 11,700 years ago, is marked by repeated glacial cycles and significant climate changes that shaped Earth's surface and ecosystems. It is characterized by the advance and retreat of massive ice sheets, leading to the formation of various landforms and influencing biodiversity, habitats, and human evolution.
Proglacial lake: A proglacial lake is a body of water that forms in front of a glacier, typically created by the melting of glacial ice and the accumulation of water as the glacier retreats. These lakes can significantly influence the surrounding landscape, including sediment deposition patterns and the formation of landforms such as deltas and outwash plains, especially during periods of Pleistocene glaciations.
Recessional Moraine: A recessional moraine is an accumulation of debris and sediment that forms at the edge of a glacier as it retreats, marking the position of the glacier during periods of temporary stability. This geological feature provides insight into the history of glacial movement and climate changes, as it indicates where a glacier paused during its overall retreat. Recessional moraines are often found in sequences that help reconstruct past glacial extents and contribute to the understanding of the landscape evolution shaped by Pleistocene glaciations.
Sediment cores: Sediment cores are cylindrical sections of sediment that are extracted from the ground or underwater to study past environmental conditions. These cores provide a chronological record of sediment deposition, allowing scientists to analyze layers for changes in climate, geology, and biological activity over time. By examining sediment cores, researchers can uncover the impacts of historical events such as Pleistocene glaciations on landscapes and ecosystems.
Stratified drift: Stratified drift refers to sediment that has been deposited by glacial meltwater in distinct layers or strata. This type of deposit often contains a mix of materials, including sand, gravel, and silt, which are sorted by the flow of the water as it transports the sediment away from the glacier. The arrangement and composition of stratified drift can reveal important information about the glacial history and the environments that existed during and after glaciation.
Terminal moraine: A terminal moraine is a type of glacial landform that forms at the edge of a glacier, consisting of debris and sediment that has been pushed forward by the moving ice. These features are significant indicators of past glacial activity and mark the furthest advance of a glacier. Terminal moraines often create ridges and mounds in the landscape, serving as evidence of the glacier's maximum extent during periods of glaciation.
U-shaped valley: A U-shaped valley is a distinctive landform created by glacial erosion, characterized by its wide, flat floor and steep, straight sides resembling the letter 'U'. This shape is formed as glaciers move through valleys, carving out the landscape and deepening the valley floor while widening its cross-section. U-shaped valleys often showcase features such as hanging valleys, cirques, and fjords, all indicative of significant glacial activity.