The Great Lakes Information Network (GLIN) is
a partnership that provides one place online for people to find
information relating to the binational Great Lakes-St. Lawrence
region of North America.
The mighty glaciers that shaped the Great Lakes have
long since disappeared, but the lakes continue to change
In Canada's north lie hundreds of thousands of lakes
deep, cold and so dear that an ordinary camera from a canoe can photograph
a fish 15 metres below the surface. In the prairies, the lakes can be
saline-so saline that brine shrimp are raised commercially. In the west,
lakes nestle in the mountains, drained by the heroic rivers that have
guided the country's destiny.
So much of Canada is dominated by waterscapes. They
are the lifeblood of agriculture and the historic routes of exploration
and development. Around them have grown up our centres of industrial
and political power. Their waters harbour the power to sculpt the bordering
lands. Yet for many of us waterscapes are "just there", little
more than background to holiday photos.
And what about the water itself? Boringly common, sometimes
a nuisance, but absolutely vital: without water our planet would be
uninhabitable. So we sink wells to tap it, build reservoirs to contain
it, devise channels, aqueducts and pipelines to carry it, erect bridges
over it, and harness it for agricultural and industrial developments.
Water also provides a focus for our play. We swim in it, sail upon it,
and frolic on the beaches it has created.
In our part of the world, water is common property,
rarely bought or sold at anything resembling its real worth. It is land,
not water that we value-that we work, bargain and fight to own. We are
terrestrial animals, dipping out toes and hoisting our umbrellas. Water
seems unimportant compared with other resources-except in times of drought
or flood, when it becomes so scarce or so abundant as to threaten our
property and our lives.
Beyond any doubt, the dominant fresh-waterscape in Canada
is that group of lakes known as the Great Lakes-the Laurentian Great
Lakes to be precise. For there are about 250 other "great"
lakes in the world-lakes with a surface area of over 500 square kilometres.
Many of them are in Canada. In fact, even discounting the Laurentian
Great Lakes, which we share with the United States, Canada can claim
about a third of all "great" lakes in the world. But this
chain of five that stretches from the St. Lawrence River valley into
the heart of the continent makes most of the others seem tiny by comparison.
On any one day the Great Lakes contain about one-fifth of the world's
surface freshwater supply. About 37 million people live in this corridor.
But though our lives are centred around these lakes, we seldom ask how
they came to be.
A Shared Lineage
More than half of the world's great lakes he north of
40 N latitude, occupying the areas that were severely glaciated during
the Great Ice Age, the Pleistocene. The glaciers around the poles and
in mountainous areas are remnants of ice that blanketed much of the
world, including most of Canada and the northern United States, within
the last two million years. Four major periods of glaciation, separated
by three interglacial periods, occurred in this time.
Little is known of the earliest events of the Pleistocene
epoch. A few sites along the shores of the present great lakes-such
as Scarborough Bluffs on Lake Ontario provide some information about
the third and last interglacial period. The evidence suggests that there
were large lakes in the Ontario and Erie basins during this time. But
we can only speculate as to the origin of the basins that contained
these and the present lakes. The history of the Great Lakes can be filled
in with some degree of certainty only for the fourth and final glacial
period, the Wisconsin.
The Wisconsin Heritage
When the Wisconsin period began, about 70,000 years
ago, the Great Lakes region was once again buried under thick, expanding
glaciers. Moving as a result of a complex process known as solid flow,
the ice picked up particles of day, sand, gravel and boulders as it
went. The glaciers "sandpapered" the bedrock, reshaped valleys
and moulded soils to form drumlins, just as previous glaciers had done.
The Wisconsin glaciers began to withdraw between 14,000
and 15,000 years ago, when the supply of ice brought to the front of
the glaciers no longer replaced what was lost to melting. As the glaciers
withdrew, they released vast quantities of meltwater, producing a variety
of topographical features. Eskers-ridges of riverbed material and gravel-were
formed. Meltwater discharge channels created and modified valleys, some
of which now harbour many of Ontario's rivers. Perhaps the most important
landforms, however, are moraines and kames, ridges and hills consisting
of mixtures of day, sand, gravel and boulders. These materials were
often deposited in contact with the ice and abandoned by the melting
glacier. Thus, the distribution of moraines and kames provides important
dues to the pattern of glacial retreat across southern Ontario.
While both the advance and the withdrawal of the Wisconsin
glaciers contributed to the shaping of the southern Ontario landscape,
the withdrawal alone was responsible for the waterscapes. Meltwaters
from the retreating glaciers formed the transitory lakes that were the
ancestors of the modem Great Lakes. The quantities of water involved
were enormous, so enormous that the outlets of the ancestral lakes could
not carry it all out of the basins. As a result, 99 percent of the waters
of the Great Lakes are today thought to be of glacial origin.
The evolution of the Great Lakes system began about
14,000 years ago and continues to this day. The ever-changing shape
of the lakes is the result of several factors: the retreat of the glaciers,
which at some time formed part of the shoreline in each of the basins;
the topography surrounding the lake, which controlled the outflow when
water levels shifted; and the gradual tilting of the earth's crust.
By about 10,000 years ago the glaciers had withdrawn from the Great
Lakes Basin; since then crustal tilting has been the major factor in
the evolution of the Great Lakes. It is still taking place today (see
Birth of the Great Lakes).
When Did We Arrive?
If we could transport ourselves back in time to the
last interglacial period, much of the landscape of the Great Lakes area
would be familiar. The depressions that now house the Great Lakes were
there and probably contained water; just as today's landscape is dominated
by the Great Lakes, the interglacial landscape was dominated by preglacial
great lakes. The rocky Precambrian Shield would be exposed much as it
is today, as would the Niagara Escarpment. As a result of previous glaciations,
we would see boulders and deposits of sand and gravel of the type that
now exist throughout the Great Lakes Basin. The Peterborough drumlin
field would not have existed, nor would other drumlin fields we can
see today, but different clusters might have formed in the same or other
areas. We would recognize the familiar erratics, those large, lonely
glacier-deposited boulders that now punctuate farmers' fields. The pattern
of the landscape would be different, but the elements would be the same
as today. There would, however, be one big difference-we would probably
be alone. There is no uncontroversial evidence of human occupation in
the Great Lakes Basin until after the last glaciation.
While it is not known for certain whether humans occupied
southern Ontario during the last interglacial period, there is good
evidence that a varied flora and fauna had developed in the climate,
which was warmer than today's. However, all living forms were obliterated
or chased out of the region with the advance of the Wisconsin glaciers.
Only their fossils remain. When southern Ontario again became free of
ice, a new biological environment was established.
When people came to the region from the south, approximately
10,200 to 11,500 years ago, they would have encountered spruce-pine
forests, many small lakes and probably one large proglacial lake (that
is, a lake in which ice forms part of the shore). The mean annual temperature
was -3 C or lower. Subsisting primarily by hunting, these early people
followed a seasonal cycle. In spring and summer, they camped on the
shore of the lakes, which would have provided rich opportunities for
hunting as well as for fishing and the gathering of edible plants. In
fall and winter, they moved inland to sheltered hunting areas, established
in smaller and more temporary campsites than those on the shore, which
were occupied over and over again.
We have little evidence for prehistoric human occupation
during the period between the earliest ancestral Great Lakes and about
10,200 years ago. Most of the evidence we do have comes from the shores
of the final stages of Lake Algonquin. If there were other, later sites
on the shores of low-level, post-Algonquin lakes, they are now deep
under water.
During the period before horticulture was introduced,
the Great Lakes and the lower reaches of the rivers draining into them
continued to attract much of the habitation in the area. A map of major
native sites during the hunting and gathering periods would trace the
shape of the Great Lakes. The garbage middens from these sites typically
contain bones of deer, beaver, muskrat, and a variety of fish species,
especially those with strong seasonal inshore and river migrations such
as sturgeon, whitefish, yellow perch, suckers, and (in Lake Ontario)
Atlantic salmon. When horticulture became important to the natives in
the southern parts of the Great Lakes Basin, a little over 1,000 years
ago, the pattern of settlement along the lakeshores became less pronounced.
As reliance on the food sources provided by the lakes diminished, there
was a general move inland. Nevertheless, lake edges continued to serve
a temporary fishing camp locations.
The Naturalist's Heritage
The changing shorelines and fluctuating lake levels
not only affected prehistoric settlement patterns, they also played
a major role in producing some of the most fascinating natural features
of the lakes. Of special interest to naturalists are the marshes formed
at the mouths of rivers and streams draining into the lakes. These environments
are perhaps the most biologically productive ecosystems of the Great
Lakes Basin. They occur in drowned valleys, which are the result of
a two-step process. First, a valley is eroded by preglacial or interglacial
rivers that flow into a lake basin. Then as water levels rise, the valleys
are flooded. Humber Marsh west of Toronto, Duffin's Creek and Whitby
marshes east of Toronto, and Cootes Paradise in Hamilton Bay (all on
Lake Ontario) are examples of marshes in drowned valleys.
Also of interest are the sandbars, sandspits and crumbling
bluffs. Erosion not only destroys old shoreline sediments, it also plays
a crucial role in the formation of new features. Rainfall, water, wind
and ice all cause erosion, but wave action is the most important, especially
during periods of high water. The owners of cottages along the base
of Long Point, for example, can attest to the havoc produced by a single
storm. In the fall of 1986, scores of homes were damaged, many obliterated,
and several floated a kilometre from their foundations. Water levels
and wave damage are cyclic-climatologists refer to a roughly 15 to 20
year cycle in precipitation, with a resulting cycle of high and low
lake levels. This is apparently old news to the natives, who spoke of
lake water being "high for seven years and low for seven years."
If cottagers lament erosion, beach and sandspit lovers
should praise it. Wasaga Beach, Long Point, Point Pelee, Presqu'ile,
Sandbanks and Toronto Islands are just some of the sand accumulations
that exist only because of erosion, which provides sand from other locations
along the shore. Long Point, which leads migrating birds one-third of
the way across Lake Erie, has historically been an island more often
than a point. During high-water years, storms have breached it. Yet
it would not exist if the same storms did not extract sand from the
bluffs to the west and leave it for longshore currents to transport
to Long Point during calmer times.
The greatest attraction on the Great Lakes is Niagara
Falls. Ninety percent the discharge from four of the five Great Lakes
passes through this magnificent cataract, visited by tens of millions
of tourists annually. The Falls were formed when Lake Iroquois still
occupied the Ontario Basin. From their original position at the edge
of the Niagara Escarpment at Queenston, the Falls cut out the present
11 kilometre gorge over a period of about 12,000 years.
Many of us are probably inclined to think of the present
configuration of the Great Lakes as their natural and final state. But
the ongoing processes of shore erosion, crustal tilting and climatic
change will continue to alter their shape and size as long as the lakes
exist. Wastes and storms will always erode and reshape the shores. The
anticipated Greenhouse Effect may reapportion the world's budget of
water, altering water levels on the lakes. By looking at the forces
that created and shaped the Great Lakes, we are reminded that their
present form is but one stage in their ongoing development.
During his tenure as curator of geology at the Royal
Ontario Museum, Dr. Tovell participated in scientific cruises for the
Great Lakes Institute, University of Toronto, to learn more about the
history of the Great Lakes. He is a former director of the museum, a
former president of FON, and the author of The Great Lakes (ROM, 1979).
This article is reprinted with permission from SEASONS,
Autumn 1987
