Glaciation and its Effects on Landscapes-Approaching-02
Looking at a topographical map of the US reveals a diverse landscape from mountains to wetlands. All of these features owe their creation to Earth’s geological events. One very impactful geological event that helped to transform Earth’s surface was the last Ice Age. The last Ice Age during the Pleistocene Epoch was actually not one single Ice Age. It was a series of glacial periods with warming periods in between. During these dramatic times of climate change, Earth was subject to both physical and chemical processes. These processes are what shaped our planet’s surface.
Imagine you are standing on a farm, far from any town in Central Illinois. What do you think you might see? Cows, pigs, perhaps a few chickens, and a lot of row crops? Now imagine ice, over a mile thick, sitting on top of this landscape. That’s how it would have been during the glacial advances of the last Ice Age.
Glacier Formation
Glaciers are masses of flowing ice. In the winter months, precipitation falls as snow or frozen rain. The accumulation of frozen precipitation builds up throughout the winter months. In the northern and southern-most latitudes, summers are very short. In times of stable global temperatures, the snow that has fallen in the winter melts during the long summer days. During an ice age, global temperatures are several degrees cooler. All the snow and ice that accumulates during the winter may not melt during the summer. The difference between how much accumulates and how much melts may be subtle. It may be only an inch or so per year. Year after year, the snow that does not melt becomes thicker and thicker.
Inch by inch, the snow starts to build up, first, over hundreds, and then, over thousands of years. Over time, these layers of snow compact and turn into ice. The ice grows thicker and thicker. Its weight causes to it to spread out. It is this action that causes the ice sheets, or glaciers, to ‘move’ or advance. Starting near the poles, the glaciers were forced southward. A few of these giant lobes of ice made it as far south as Illinois.