Lake Bonneville remnant is Great Salt Lake Periglacial near ice environments

Lake bonneville remnant is great salt lake

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Lake Bonneville (remnant is Great Salt Lake) - Periglacial (near-ice) environments are unique - Characterized by year-round frozen ground (permafrost) - Freeze-thaw cycles generate unusual patterned ground Pleistocene ice ages - Young (<2.6 Ma) glacial remnants are abundant - Northern North America - Scandinavia and Europe - Siberia - Landscapes in these regions are clearly glacial Pleistocene life and climate - All climate and vegetation belts were shifted southward - The tundra limit was 48 degrees N. Today, it is above 68 degrees N - Vegetation evidence is preserved as pollen found in bogs - Pleistocene fauna were well adapted - Mammals included now-extinct giants:
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- Giant beaver - Giant ground sloth - Mammoths and mastodons - Modern humans proliferated Timing of the Pleistocene Ice Age - In North America, multiple Pleistocene glacial advances are recognized. Youngest to oldest: - Wisconsinan - Illinoian - Pre-illinoian - Ice ages separated by interglacials intervals - Oxygen isotopes suggest twenty or more glaciations throughout Earth's history - Higer 18 O/ 16 O = colder - Lower 18 O/ 16 O = warmer - The “original four” ice ages may simply have been the largest Earlier glaciations - Glaciations have occurred before in Earth's history - They are indicated by fossil tills and striated bedrock: - Pleistocene (since 2.5 Ma ago) - Permian - Ordovician - Late Proterozoic - tillites at equatorial latitudes suggest an ice-covered world (“Snowball Earth”) Causes of glaciation - Long-term causes - set the stage for ice ages - Plate tectonics - control factors that influence glaciation - Distribution of continents toward high latitudes - Sea-level flux by mid-ocean-ridge volume changes - Oceanic currents - Atmospheric chemistry - Changes in greenhouse gas concentrations - Carbon dioxide - Methane - Global average temperature today: 14 degrees celsius - Short-term causes - govern advances and retreats - Milankovitch hypothesis - climate variation over 100 to 300 ka predicted by cyclic changes in orbital geometry - The shape of Earth’s orbit varies (100,00 year cyclicity) - Tilt of Earth’s axis varies from 22.5 to 24.5 (41,000 years) - Precession - earth’s axis wobbles like a top (23,000 years) - Milankovitch cycle drive global climate and glacial cycles
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- Stage 1: average temperature drops, glaciers are born - Stage 2: glaciers grow, albedo causes further cooling - Stage 3: temperatures warm, glaciers shrink, interglacial begins Will there be another glaciation? - We are living in an interglacial. Ice will return! But when? - Recent interglacials have lasted 10,000 years - But, it has been 11,000 years since the last deglaciation - A cool period (1300-1850) resulted in the Little Ice Age - We may have forestalled the next glaciation…. How? - During the last 150 years, temperatures have risen and most mountain glaciers have dramatically retreated - Earth’s climate could now be in “super-interglacial” period - This current interglacial might be in extension because of human-induced warming
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  • Fall '09
  • ALFONSOMUCCI
  • Glacier, valley glacier, Glacial Lake Agassiz

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