Physical Processes
Glaciation
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Glaciation is the shaping of landscapes by moving ice, through two distinct erosional mechanisms: abrasion, in which rock and debris embedded in a glacier's base grind the bedrock beneath it, and plucking, in which the ice pulls loose entire blocks of fractured rock. As glaciers advance and retreat they carve distinctive landforms, and the sediment they carry is deposited as moraines when the ice melts.
Facts
Process Type TimescaleGlacial advance and retreat play out over centuries to millennia; the ice itself typically flows at a rate of centimeters to a few meters per day. 1 First Proposed YearLouis Agassiz proposed that the Earth had undergone a past ice age, presenting the theory (developed with Karl Schimper) to the Swiss Society for Natural Research at Neuchatel on 24 July 1837. Scientific Consensus YearThe ice age theory was fully accepted by scientists on an international scale during the second half of the 1870s, following the work of James Croll; 1875 is recorded here as a representative midpoint of that span, not a single defining event. Cross-Tradition Connections
Demonstrated By
An active ice sheet presently carrying out glacial erosion and deposition at continental scale.
Shaped
Sources
1. U.S. National Park Service
U.S. National Park ServiceHow Glaciers Change the LandscapeQuote, How Glaciers Change the Landscape
Glaciers can sculpt and carve landscapes by eroding the land beneath them and by depositing sediment.
1. U.S. National Park Service
U.S. National Park ServiceDemonstrated By: The Antarctic Ice SheetView the Source 2. Louis Agassiz (Wikipedia)
Wikimedia FoundationIce age sectionQuote, Ice age section
In 1837, Agassiz proposed that the Earth had been subjected to a past ice age.
3. Ice Age (Wikipedia)
Wikimedia FoundationHistory of research sectionQuote, History of research section
This happened on an international scale in the second half of the 1870s, following the work of James Croll
The Formation of the Great Lakes (Wisconsin Sea Grant)
Wisconsin Sea Grant, University of Wisconsin-MadisonShaped: The Great Lakes, How They Were MadeQuote, Shaped: The Great Lakes, How They Were Made
Thousands of years ago, the melting mile-thick glaciers of the Wisconsin Ice Age left the North American continent a magnificent gift: five fantastic freshwater seas collectively known today as the Great Lakes.
U-Shaped Valleys, Fjords, and Hanging Valleys (U.S. National Park Service)
U.S. National Park ServiceShaped: The Alps, U-Shaped Valleys sectionQuote, Shaped: The Alps, U-Shaped Valleys section
Valley glaciers carve U-shaped valleys, as opposed to the V-shaped valleys carved by rivers.
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