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 formed due to the St. Lawrence River being blocked downstream by an ice sheet near the present Thousand Islands. 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. Glacial Lake Iroquois 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.
In Toronto, Ontario this ridge can be seen paralleling Davenport Road near Spadina Avenue. In Scarboiriugh, Ontario it can be seen where the prehistoric shoreline takes the form of earthen cliffs at the modern lakeshore (called the Scarborough Bluffs). In New York, Ridge Road and parts of Route 104 sit atop the ridge.
Intent:
The purpose of this Earthcache is to illustrate the difference in size of the current Lake Ontario and former Lake Iroquois. As you travel from the starting location to the final location, you will be traveling through the former glacial lake bottom.
Formation:
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.
Sometime 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 Ice age. 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.
With thanks:
This is a sister cache to “Great Lakes – Lake Iroquois” (http://coord.info/GC127DY) in Toronto by TnT. And much thanks to TnT for collating the information.
More information:
http://en.wikipedia.org/wiki/Glacial_Lake_Iroquois
http://www.lostrivers.ca/points/Lake_Iroquois.htm
https://abitmoredetail.wordpress.com/tag/glacial-lake-iroquois/
http://www.whoi.edu/oceanus/feature/the-great-flood-of-new-york
http://www.niagarafrontier.com/origins.html#e
http://www.rasny.org/geostory/glacigeo.htm
To claim this find, you must gather some information.
- At the Posted coordinates, what is your staring elevation on top of Ridge Road
- At the Final coordinates what is your ending elevation on Washington Street
- How many miles is Ridge Road from the present shoreline
- Calculate your average drop per mile
- Estimate the current lake level
Please send me the above information. You may log the claim right away, but please send me the above information in a timely manner or I will delete your log.
- Optional: Upload a photo of the lake at the time of your visit. It would be interesting to document the changing lake over time.
Note: There is a small pocket park at the final coordinates. There are a few placards depicting some local history. On one of the placards is a map of several buildings and the shoreline as it appeared over 150 years ago. Notice how much shoreline has been eroded over the past 150 years.