Glacial Lake Iroquois was a prehistoric

proglacial lake In geology, a proglacial lake is a lake formed either by the damming action of a moraine during the retreat of a melting glacier, a glacial ice dam, or by meltwater trapped against an ice sheet due to isostatic depression of the crust around th ...

that existed at the end of the last

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gre ...

approximately 13,000 years ago. The lake was essentially an enlargement of the present

Lake Ontario Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north, west, and southwest by the Canadian province of Ontario, and on the south and east by the U.S. state of New York. The Canada–United States border ...

that formed because the

St. Lawrence River The St. Lawrence River (french: Fleuve Saint-Laurent, ) is a large river in the middle latitudes of North America. Its headwaters begin flowing from Lake Ontario in a (roughly) northeasterly direction, into the Gulf of St. Lawrence, connecting ...

downstream from the lake was blocked by the ice sheet near the present

Thousand Islands The Thousand Islands (french: Mille-Îles) constitute a North American archipelago of 1,864 islands that straddles the Canada–US border in the Saint Lawrence River as it emerges from the northeast corner of Lake Ontario. They stretch for abo ...

. The level of the lake was approximately 30 m (~100 ft) above the present level of Lake Ontario. The work of Anderson and Lewis (1985) is the basis for these authors' views on the history of the postglacial water levels. Glacial lakes

The lake drained to the southeast, through a channel passing near present day

Rome, New York Rome is a city in Oneida County, New York, United States, located in the central part of the state. The population was 32,127 at the 2020 census. Rome is one of two principal cities in the Utica–Rome Metropolitan Statistical Area, which li ...

. The

Rome Sand Plains Rome Sand Plains is a pine barrens about west of the city center of Rome in Oneida County in central New York. It consists of a mosaic of sand dunes rising about above low peat bogs that lie between the dunes. The barrens are covered with mix ...

has several sand ridges that geologists think were formed at this time. The channel then followed the valley of the

Mohawk River The Mohawk River is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed October 3, 2011 river in the U.S. state of New York. It is the largest tributary of the Hudson River. The Mohawk f ...

to the

Hudson River The Hudson River is a river that flows from north to south primarily through eastern New York. It originates in the Adirondack Mountains of Upstate New York and flows southward through the Hudson Valley to the New York Harbor between N ...

. The lake was fed by

Early Lake Erie Early Lake Erie was a prehistoric proglacial lake that existed at the end of the last ice age approximately 13,000 years ago. The early Erie fed waters to Glacial Lake Iroquois. The ancient lake was similar in size to the current lake during glaci ...

, as well as

Glacial Lake Algonquin Lake Algonquin was a prehistoric proglacial lake that existed in east-central North America at the time of the last ice age. Parts of the former lake are now Lake Huron, Georgian Bay, Lake Superior, Lake Michigan, Lake Nipigon, and Lake Nipissing ...

, an early partial manifestation of Lake Huron, that drained directly to Lake Iroquois across southern

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central C ...

, 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 The Younger Dryas (c. 12,900 to 11,700 years BP) was a return to glacial conditions which temporarily reversed the gradual climatic warming after the Last Glacial Maximum (LGM, c. 27,000 to 20,000 years BP). The Younger Dryas was the last stag ...

episode.

Remnant shorelines

Two ancient shorelines in the

Toronto Toronto ( ; or ) is the capital city of the Canadian province of Ontario. With a recorded population of 2,794,356 in 2021, it is the most populous city in Canada and the fourth most populous city in North America. The city is the anch ...

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 Davenport Road is an east–west arterial road in Toronto, Ontario, Canada. It is believed to follow an old native trail along the foot of the scarp of the old shoreline of glacial Lake Iroquois. It currently runs from Yonge Street in the eas ...

just south of St. Clair Avenue West. Further east, the

Scarborough Bluffs The Scarborough Bluffs, also known as The Bluffs, is an escarpment in the Scarborough district of Toronto, Ontario, Canada. There are nine parks along the bluffs, with Bluffers Park being the only one with a beach. Forming much of the eastern ...

also formed part of the shoreline of the ancient lake. In Mississauga, the shoreline is found south of Dundas Street and most visible with hills found east and west of Mavis Road. 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. In New York, Ridge Road and

New York State Route 104 New York State Route 104 (NY 104) is a east–west state highway in Upstate New York in the United States. It spans six counties and enters the vicinity of four cities—Niagara Falls, Lockport, Rochester, and Oswego—as it follow ...

run from west to east along a ridge of the old shoreline of Lake Iroquois.

References

External links

History of Lake Iroquois
showing map of the lake
Deglaciation of the Central St. Lawrence Lowland
{{DEFAULTSORT:Iroquois, Lake Natural history of Ontario Proglacial lakes Geology of New York (state) Glacial lakes of Canada

Remnant shorelines

See also

References

External links