Glacial Lake Iroquois was a prehistoric proglacial lake that existed at the end of the last ice age approximately 13,000 years ago. 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.
The Lake drained to the southeast, through a channel passing near present day Rome, New York. The channel then followed the valley of the Mohawk River to the Hudson River.
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, and setting off the Younger Dryas episode.
The prehistoric shoreline, marked by a ridge known as the Iroquois Shoreline, can be discerned in places around Lake Ontario. This can be seen, for instance, in Toronto paralleling Davenport Road near Spadina Avenue, and also nearby in Scarborough, Ontario, where the prehistoric shoreline takes the form of earthen cliffs at the modern lakeshore (called the Scarborough Bluffs).
The lake was carved out of soft, weak Silurian rocks by the Wisconsonian ice age glacier, which expanded the preglacial Ontarian River valley of approximately the same orientation. The material that was pushed southward was piled in central and western New York in the form of drumlins, kames, and moraines, which reorganized entire drainage systems. As the glacier retreated from New York, it still dammed the present St. Lawrence valley, so that the lake was at a higher level. This state is known as Lake Iroquois. During that time the lake drained through present-day Syracuse, New York into the Mohawk River. The old shoreline that was created during this lake stage can be easily recognized by the (now dry) beaches and wave-cut hills 10 to 25 miles (15 to 40 km) south of the present shoreline.
When the glacier finally melted from the St. Lawrence valley, the outlet was below sea level, and the lake became for a short time a bay of the ocean. Gradually the land rebounded from the release of the weight of about 6,500 feet (2000 m) of ice that had been stacked on it. It is still rebounding about 12 inches (30 cm) per century in the St. Lawrence area. Since the ice left that area last, that is the area where the most rapid rebound still is occurring. This means that the lake bed is gradually tilting southward, inundating the south shore and turning river valleys into bays. Both north and south shores have shoreline erosion, but the tilting amplifies this effect on the south shore, causing loss to property owners.
The Wisconsin or Wisconsinian was the last major advance of continental glaciers in North America. This glaciation is made of three glacial maximums (commonly called ice ages) separated by interglacial periods (such as the one we are living in). These ice ages are called (from oldest to youngest); Tahoe, Tenaya and Tioga. The Tahoe reached its maximum extent perhaps about 70,000 years ago. Little is known about the Tenaya. The Tioga was the least severe and last of the Wisconsinan group. It began about 30,000 years ago, reached its greatest advance 20,000 years ago, and ended about 10,000 years ago. At the height of glaciation the Bering land bridge permitted migration of mammals and humans to North America from Siberia
It radically altered the geography of North America north of the Ohio River. At the height of the Wisconsin glaciation, ice covered most of Canada, the Upper Midwest, and New England, as well as parts of Montana and Washington. On Kelleys Island in Lake Erie or in New York's Central Park, the grooves left by these glaciers can be easily observed. In southwestern Saskatchewan and southeastern Alberta a suture zone between the Laurentide and Cordilleran ice sheets formed the Cypress Hills, which is the northernmost point in North America that remained south of the continental ice sheets.
The Great Lakes are the result of glacial scour and pooling of meltwater at the rim of the receding ice. When the enormous mass of the continental ice sheet retreated, the Great Lakes began gradually moving south due to isostatic rebound of the north shore. Niagara Falls is also a product of the glaciation, as is the course of the Ohio River, which largely supplanted the prior Teays River.
In its retreat, the Wisconsin glaciation left terminal moraines that form Long Island, Nantucket and Cape Cod, and the Oak Ridges Moraine in south central Ontario, Canada. The drumlins and eskers formed at its melting edge are landmarks of the Lower Connecticut River Valley.
During the final retreat of the Laurentide Ice Sheet, ice blocked the St. Lawrence valley causing meltwater to flood the Lake Ontario basin and create glacial Lake Iroquois. Distinctive features of the Lake Iroquois shoreline are its prominent shorebluff, and large sand and gravel bars deposited in the Don and Humber river valleys. Downtown Toronto was submerged and is built on the old lake bottom. The Lake Iroquois shoreline also forms the headwaters for smaller streams such as Petticoat and Highland creeks. Sand and gravel deposited along the shore of Lake Iroquois were mined for construction and clay from the former lake bottom was used to make bricks.
About 12 000 years ago, glacial Lake Iroquois formed a shoreline around the Lake Ontario basin while glacial Lake Algonquin formed its shoreline around the Lake Simcoe basin.
Former aggregate pits and landfills along Lake Iroquois shoreline.
Historically, the natural shore of Lake Ontario was at Front Street. Since the 1850s the Toronto shoreline has been extended almost 1 kilometre into the harbour by dumping millions of tonnes of fill. This originally provided land for industry and shipping. Now this land is used for condominiums, hotels, and parks. More recently, filling has occurred to reduce shoreline erosion and to build parks and marinas such as Bluffer's Park and Ontario Place.
Filling since 1850 has created lots of new land in the Toronto harbour area.
Some time between thirteen and twelve thousand years ago, the ice disappeared from the Lake Ontario basin and the lake waters which had had to use southern and western outlets at a higher level, found an outlet into the Hudson River near Rome, New York. As this was higher than today's St. Lawrence outlet, a high level lake we know as Lake Iroquois formed.
The crustal block that underlies most of The Province of Quebec and north-eastern Ontario,together with the eastern end of Lake Ontario and the St. Lawrence valley had been under as much as 2 km of ice for over 100,000 years and thus had been pushed hundreds on metres down into the mantle. The western end of the lake was freed from the ice several thousand years earlier than the eastern end, and probably had only been under the ice sheet for a small part of the Wisconsinan iceage. As a result it rebounded first, tilting that end of the Lake Ontario basin up at the time of Lake Iroquois (and for some time after). The eastern end of Lake Ontario and the St. Lawrence valley, having been depressed more, have rebounded more; thus the present in level of the Lake Iroquois shoreline varies from 55 metres above sea level near the Humber to 68 metres at the east end of Scarborough.
Into that cold glacial lake flowed a number of streams which are now tributaries of the Don River, including Castle Frank Brook, Yellow Creek and Mud Creek. See above map of the Toronto shoreline 12,000 years ago. All of downtown below Davenport Road was under the icy waters of Lake Iroquois. Much of Leaside was covered by a shallow bay, some times referred to as a lagoon, because it was cut off from the lake by a sand bar along today's Danforth Ave.
For the last two million years or so, large parts of the northern hemisphere, all of Antarctica and many mountain chains on other continents have been covered and recovered by ice sheets. The surface of most of Canada has been shaped by the advancing and retreating of these glaciers. Most of Great Lakes' basins of and other Canadian lakes both large and small were carved out by the moving ice. Soil and rocks were scooped off the Canadian Shield and deposited over southern parts such as Toronto.
Many causes have been suggested for the Pleistocene Glaciation and others earlier in our planet's history including: changes in solar flux; changes in the shape of Earth's orbit & the tilt its axis; the massing of the continents and deep oceanic currents. Probably it was a combination of several such influences.
North America's continental ice sheet apparently started in Labrador or Ungava then spread south in the east and west in the north. Other ice sheets grew from the coalescing of mountain glaciers in the west and in the Arctic. We may be closer to new continental ice sheets than we think. There are many such ice fields in that area. What would it take for these small ice fields to join and grow into a glacier covering Labrador and Quebec? Whenever a combination of cold climate and sufficient precipitation in the form of snow occurs, as it has several times in the past few million years and in the more distant past, continental glaciers form and grow.
To log this earthcache you will need to complete the following.
1.Take a picture of yourself with the Lake in the background and post it with your log.
2.Measure the elevation of the lake and email it to me, how do you think the elevation has changed in the past 100 years?