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Unlock your guides7.4 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)
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