Editing Great Lakes (section)

==Geology==
[[File:Glacial lakes.jpg|thumb|right|upright=1.5|A diagram of the formation of the Great Lakes]]
[[File:Champlain Sea 1.png|thumb|upright=1.5|The [[Champlain Sea]] - The best evidence of this former sea is the vast clay plain deposited along the [[Ottawa River|Ottawa]] and [[St. Lawrence River|St. Lawrence Rivers]].<ref>Chapman, L.J. and D.F. Putnam. 1984. ''The Physiography of Southern Ontario''. Third edition. Ontario Geological Survey, Special Volume No.2. Government of Ontario, Toronto.</ref> ]]
It has been estimated that the foundational geology that created the conditions shaping the present day upper Great Lakes was laid from 1.1 to 1.2&nbsp;billion years ago,<ref name="Grady" /><ref name=Schmus>{{cite journal |last1 = Van Schmus |first1 = W.R. |last2 = Hinze |first2 = W. J. |title = The Midcontinent Rift System |journal = Annual Review of Earth and Planetary Sciences |volume = 13 |issue = 1 |pages = 345–83 |date = May 1985 |url = https://kuscholarworks.ku.edu/dspace/bitstream/1808/104/1/fac6cit13.pdf |doi = 10.1146/annurev.ea.13.050185.002021 |access-date = October 6, 2008 |hdl = 1808/104 |bibcode = 1985AREPS..13..345V |hdl-access = free }}</ref> when two previously fused [[tectonic plates]] split apart and created the [[Midcontinent Rift System|Midcontinent Rift]], which crossed the [[Great Lakes Tectonic Zone]]. A valley was formed providing a basin that eventually became modern day Lake Superior. When a second fault line, the [[Saint Lawrence rift system|Saint Lawrence rift]], formed approximately 570&nbsp;million years ago,<ref name="Grady" /> the basis for Lakes Ontario and Erie was created, along with what would become the Saint Lawrence River.

The Great Lakes are estimated to have been formed at the end of the [[Last Glacial Period]] (the [[Wisconsin glaciation]] ended 10,000 to 12,000 years ago), when the [[Laurentide Ice Sheet]] receded.<ref name="CordellLightfoot2008"/> The retreat of the ice sheet left behind a large amount of meltwater ([[Lake Algonquin]], [[Lake Chicago]], [[Glacial Lake Iroquois]], and [[Champlain Sea]]) that filled up the basins that the glaciers had carved, thus creating the Great Lakes as they are today.<ref>{{cite journal |last1 = Larson |first1 = Grahame |last2 = Schaetzl |first2 = R. |title = Origin and evolution of the Great Lakes |journal = Journal of Great Lakes Research |volume = 27 |issue = 4 |pages = 518–546 |year = 2001 |url = http://www.geo.msu.edu/schaetzl/PDFs/Larson-Great_lakes.pdf |doi = 10.1016/S0380-1330(01)70665-X |bibcode = 2001JGLR...27..518L |access-date = March 4, 2009 |archive-url = https://web.archive.org/web/20081031073825/http://www.geo.msu.edu/schaetzl/PDFs/Larson-Great_lakes.pdf |archive-date = October 31, 2008 }}</ref> Because of the uneven nature of glacier [[erosion]], some higher hills became Great Lakes islands. The Niagara Escarpment follows the contour of the Great Lakes between New York and Wisconsin. Land below the glaciers [[Post-glacial rebound|"rebounded"]] as it was uncovered.<ref>{{cite web |url = http://greatlakesecho.org/2009/06/08/lake-levels-report-weighs-great-lakes-basins-glacial-legacy/ |title = Lake levels report weighs Great Lakes basin's glacial legacy |publisher = Great Lakes Echo |date = June 8, 2009 |access-date = February 19, 2011 }}</ref> Since the glaciers covered some areas longer than others, this glacial rebound occurred at different rates.