Glaciation: Definition, Periods & Causes

Instructor: Christopher Sailus

Chris has an M.A. in history and taught university and high school history.

In this lesson, we explore glaciation. Referring to the movement and formation of glaciers, glaciation has played an important role in human history, including allowing for the implementation of one of humanity's most important practices.

Ice, Big and Small

Most people encounter ice on an everyday basis. If you live in southern California, chances are the only ice you ever encounter is the cube form that you place in your water every day, but those of us who live in America's northern states can assure you: ice is a natural part of the environment, whether you like it or not. Indeed, some of us spend countless hours scraping ice off our car windows every winter morning, or spend our weekends skating on the ice that seals in our northern lakes every year.

While northerners encounter naturally occurring ice outdoors, it's doubtful that any North Dakotans or Michiganders have ever seen ice's largest and most powerful formation: glaciers. Glaciers are sheetlike walls of ice that move incredibly slowly. Indeed, the fastest glacier today, the Jakobshavn Glacier in Greenland, moves only 20 meters per day!

The term glaciation refers to the movement and formation of these megalithic wintry features. Glaciation is important because, while slow, the actions of glaciers can affect ocean levels, ocean salinity, earth's reflectivity, and the overall climate over long periods of time. As such, they have played a pivotal role in human history.

Glaciation in History

The amount and size of glaciers have fluctuated wildly throughout the Earth's history, with periods of expansion and recession often lasting thousands of years. The most recent glacial period, and the one most important for human history, occurred over nearly 100,000 years in our relatively recent past.

Termed the Wisconsin glacial period in North America, the glaciers reached their largest extent about 18,000 years ago when large sheets of ice covered all of Canada, New England, Michigan, and large portions of other northern states.

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