Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
by Taran Wakatani
The Great Lakes
The Great Lakes are a collection of five freshwater lakes in the northeastern
North America. The lakes names, Huron, Ontario, Michigan, Erie and Superior, can
also be abbreviated as HOMES. Together they contain twenty-one percent of
earth’s freshwater and form the largest group of freshwater lakes in the world
with 6 quadrillion gallons of fresh water. It
took a lot of time for nature to craft what today is the Great Lakes.
Great Lakes Basin (the Great Lakes and the surrounding area) began to form about
two billion years ago – almost two-thirds the age of the earth. During this
period, major volcanic activity and geologic stresses formed the mountain
systems of North America, and after significant erosion, several depressions in
the ground were carved. Some two billion years later the surrounding seas
continuously flooded the area, further eroding the landscape and leaving a lot
of water behind as they went away.
More recently, about two million years ago, it was glaciers that advanced over and back across the land. The glaciers were upwards of 6,500 feet thick and further depressed the Great Lakes Basin. When the glaciers finally retreated and melted approximately 15,000 years ago, massive quantities of water were left behind. It is these glacier waters that form the Great Lake today.
Many glacial features are still visible on the Great Lakes Basin today in the form of "glacial drift," groups of sand, silt, clay and other unorganized debris deposited by a glacier. Moraines, till plains, drumlins, and eskers are some of the most common features that remain.
94,250 square miles of water for all five lakes, there have been major
development on the shores of these lakes. Touching eight states in the U.S. and
Ontario in Canada, it made an excellent site for the transportation of goods.
There are over 120 cities on these shores and some of the biggest cities in the
region. Some of the biggest are Buffalo, Cleveland, Toledo, Bay City, Chicago,
Green Bay, Milwaukee, Toronto and Traverse City. It is estimated that there are
over 35 million people living in this area. It was the primary route used by
early explorers of North America, and was a major reason for the great
industrial growth of the Midwest throughout the 19th and 20th century.
The history of shipping practices in the Great Lakes begins in 1825, when the
Erie Canal was used to carry settlers west and to carry freight east. The St.
Lawrence Seaway was completed in 1959 and allowed ocean vessels access to the
Great Lakes for shipping purposes. Over 200 million tons of cargo are shipped
every year through the Great Lakes. The three main cargoes are iron ore, coal,
and grain. But it also promotes many jobs for the industry. According to the
comprehensive study, "The Economic Impacts of the Great Lakes-St. Lawrence
Seaway System," more than 225,000 good-paying jobs are dependent upon commercial
maritime activity in the geographic area that stretches over 2,300 miles between
Duluth-Superior and Montreal. The majority of these jobs–more than 128,000–are
in the United States.
In addition to creating necessary jobs, the Seaway system generates billions of
dollars in income and revenues annually in both the U.S. and Canada. The new
study found that maritime activity on the waterway supported $34 billion in
business revenue, $14 billion in personal income, and $4.6 billion in federal,
state, provincial, and local tax revenue. It also 250 species of fish.
The Great Lakes provide drinking water for 40 million people and 56 billion
gallons of water per day for municipal, agricultural, and industrial use. But it
also adds some of the best fishing in North America.
Commercial and sport fisheries are important industries in the Great Lakes region. Commercial fishing began in about 1820 and has increased ever since. About 65 million pounds of fish per year are harvested from the lakes, contributing more than $4 billion to the Great Lakes economy. Primary commercial catches include whitefish, smelt, walleye, and perch, while sport anglers prefer salmon, steelhead, walleye, lake trout, perch and bass; although there are over 250 species of fish in the Great Lakes. The lakes do have some effect on the local climate though.
Lake effect is bad news for people who dislike the snow. Lake-effect snow is produced during cooler atmospheric conditions when cold winds move across long expanses of warmer lake water, providing energy and picking up water vapor, which freezes and is deposited on the leeward shores. The same effect also occurs over bodies of salt water, when it is termed ocean-effect or bay-effect snow. The effect is enhanced when the moving air mass is uplifted by the orographic influence of higher elevations on the downwind shores. This uplifting can produce narrow but very intense bands of precipitation, which deposit at a rate of many inches of snow each hour, often resulting in copious snowfall totals.