Glaciers

UNIT 3

Glaciers & the Ice Age

Most of the surface of Minnesota was shaped by glaciers, large sheets of ice covering land that are thousands of feet thick. Many years ago, during a time called the Ice Age, parts of the world became very cold. Heavy snow fell, and it was so cold in the northern part of the North American continent that much of the snow never melted. As the snow grew deeper from year to year, it turned to ice, forming large glaciers. After a while, these glaciers started moving southward.

Four of these great ice masses spread over Minnesota at four different times. After each advance of ice, warmer weather melted the glaciers. Then cold weather would cause another glacier to form. The last of these huge ice masses melted and disappeared from Minnesota about 10,000 years ago.

glacier: a moving sheet of ice thousands of feet thick

Ice Age: a long period of time when temperatures are very cold and glaciers cover large parts of the earth

How Glaciers Changed Minnesota

As the glaciers moved slowly over the land, they leveled off hills and mountains and ground up many rocks into fine soil. The ice carried along this soil mixed with loose rocks. When the ice melted, this material was left behind. It is called glacial drift and is hundreds of feet thick in some parts of Minnesota.

Thanks to the glaciers that once covered our state, one of Minnesota's largest economies is farming. By rounding off hills and dropping fine soil, the glaciers made large parts of Minnesota into level farmlands with rich soil. In other places, however, large rocks were left behind by the melting glaciers. These rocks had to be removed before the land could be farmed which posed a challenge to people that established farms in these areas. The glaciers also made some land in Minnesota too steep or swampy for farming.

Summers in Minnesota are also busy times for vacationers heading north to retreat to a family lake cabin. Just like our rich farm fields can be attributed to the glaciers, cabin country was also formed by the glaciers! Most of the lakes in Minnesota were formed by glaciers. The heavy glaciers dug shallow holes in the glacial drift. As the ice melted, these hollows filled up with water and became lakes. Some of the lakes dried up, leaving level flat land with rich soil. The Red River Valley, for example, was once the bottom of a huge glacial lake called Lake Agassiz.

glacial drift: rock and soil left behind by glaciers

glacial lake: very large lakes left behind by the glaciers

Lake Agassiz: one of the largest glacial lakes in Minnesota

< Large glacial lakes left behind by the melting glaciers covered large parts of North America. Lake Agassiz covered the northwest portion of Minnesota. When it dried up, it left behind the rich soil in the Red River Valley

While most parts of Minnesota were covered by glaciers and buried under glacial deposits, the southeast corner of Minnesota that has escaped the crushing of the glaciers. Millions of years of uninterrupted erosion have spectacularly carved out the landscape of the Driftless Area, creating 150+ bluffs and narrow valleys. This landscape stands out in sharp contrast to the flatter glaciated areas which surround it.

driftless area: portion of Minnesota that was not covered by glaciers; located in southeastern Minnesota

Gifts of the Glaciers

GOOD TOPSOIL

One of the benefits the glaciers gave Minnesota is the good topsoil carried down from Canada. We do not know for sure what kind of soil we would have if the glaciers were never in our state.

WATER HIGHWAY

The glaciers also gave us the Great Lakes. These lakes serve as a great waterway that we use to carry the products of our industries and mines to many parts of the country.

MOISTURE

The glaciers also gave Minnesota its lakes. These lakes account for hundreds of thousands of acres--Minnesota actually has more shoreline than the state of California!

The lakes not only give us beauty and opportunities for swimming, fishing, and boating, they also supply water for crops and drinking.

NEGATIVE EFFECTS OF GLACIERS

The glaciers gave us many benefits but at some cost. They made a waste land out of part of Minnesota which is not bare rock or swamp land. They covered our iron ore and perhaps other minerals with glacial drift. Much of the drift left behind is poor soil with much gravel and stones. It is only useful for growing trees.

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