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Lake Iroquois
Lake Iroquois
	This map shows the valley of the Mohawk River, through which Glacial Lake Iroquois crossed the mountains to the Hudson River Valley.
	Lake Iroquois
Location	North America
Group	Great Lakes
Coordinates	43°42′N 77°54′W / 43.7°N 77.9°W
Lake type	former lake
Etymology	Iroquois or Haudenosaunee (/ˈhoʊdənoʊˈʃoʊni/; "People of the Longhouse")
Primary inflows	Niagara River
Primary outflows	Mohawk River to the Hudson River
Basin countries	Canada; United States
Max. length	196 mi (315 km)
Max. width	57 mi (92 km)
Surface elevation	345 ft (105 m)
References	United States Geological Survey, George Otis Smith, Director; The Pleistocene of Indiana and Michigan and the History of the Great Lakes; Frank Leverett and Frank B. Taylor; Department of the Interior, Monographs of the United States Geological Survey; Volume LIII; Washington; Government Printing Office; 1915

Glacial Lake Iroquois was a prehistoric proglacial lake that existed at the end of the last ice age approximately 13,000 years ago.^[2]

Description

The lake was essentially an enlargement of the present Lake Ontario that formed because the St. Lawrence River downstream from the lake was blocked by the ice sheet near the present Thousand Islands. The level of the lake was approximately 30 m (~100 ft) above the present level of Lake Ontario.^[3]

The lake drained to the southeast, through a channel passing near present day Rome, New York. The Rome Sand Plains has several sand ridges that geologists think were formed at this time. The channel then followed the valley of the Mohawk River to the Hudson River.^[3]

The lake was fed by Early Lake Erie, as well as Glacial Lake Algonquin, an early partial manifestation of Lake Huron, that drained directly to Lake Iroquois across southern Ontario, along the southern edge of the ice sheet, bypassing Early Lake Erie.

The subsequent melting of the ice dam resulted in a sudden lowering of the lake to its present level, a potential trigger for the Younger Dryas episode.^[4]

Remnant shorelines

Two ancient shorelines in the Toronto area mark the existence of former glacial lakes. About 2 km inland from the shore, a ridge known as the Iroquois Shoreline can be discerned. The old shoreline runs west-east, running roughly parallel to Davenport Road just south of St. Clair Avenue West. Further east, the Scarborough Bluffs also formed part of the shoreline of the ancient lake.^[5] In Mississauga, the shoreline is found south of Dundas Street and most visible with hills found east and west of Mavis Road.^[6]

Another ancient shoreline exists between 2–4 km offshore of Toronto. It is known as the Toronto Scarp and formed the shore of Glacial Lake Warren or Admiralty Lake. From Bluffer's Park in Scarborough to just west of Hanlan's Point is an underwater bluff.^[7]

In Hamilton, Ontario the Burlington Heights represents a sand and gravel bar formed across the mouth of Cootes Paradise, at the western end of Glacial Lake Iroquois.

In New York, Ridge Road and New York State Route 104 run from west to east along a ridge of the old shoreline of Lake Iroquois.^[8]

References

^ Beauchamp, William Martin (1905). A History of the New York Iroquois. New York State Education Department. p. 165. Retrieved May 7, 2016.
^ Richard Foster Flint (2008). Glacial Geology and the Pleistocene Epoch. Read Books. ISBN 978-1-4437-2173-8.
^ ^a ^b Larson, Grahame; Schaetzl, Randall (2001). "Review: Origin and Evolution of the Great Lakes" (PDF). J. Great Lakes Res. 27 (4): 518–546. doi:10.1016/S0380-1330(01)70665-X. Archived from the original (PDF) on 2008-10-31. The work of Anderson and Lewis (1985) is the basis for these authors' views on the history of the postglacial water levels.
^ Donnelly, Jeffrey P.; Neal W. Driscoll; Elazar Uchupi; Lloyd D. Keigwin; William C. Schwab; E. Robert Thieler; Stephen A. Swift (February 2005). "Catastrophic meltwater discharge down the Hudson Valley: A potential trigger for the Intra-Allerød cold period". Geology. 33 (2): 89–92. Bibcode:2005Geo....33...89D. doi:10.1130/G21043.1.
^ Eyles, Nick (2002). Ontario Rocks: Three Billion Years of Environmental Change. Markham, Ontario: Fitzhenry & Whiteside. ISBN 9781550416190. OCLC 48940760. See chapter 17.
^ "Natural Areas Survey (NAS) Site: ER6" (PDF). mississauga.ca. Retrieved 2023-07-10.
^ "Nearshore Geology". City of Toronto TRC. n.d. Archived from the original on 26 February 2012. Retrieved 26 December 2009.
^ Tesmer, Irving H.; Bastedo, Jered C. (1981). Colossal cataract: the geologic history of Niagara Falls. SUNY Press. p. 48. ISBN 978-0-87395-522-5. Retrieved 2 February 2010.