Introduction
This area north of Lebanon, Indiana illustrates the flatness of the glaciated portion of Indiana. The glacial till yields the most productive soils for growing crops, in this case for Gutwein Gourmet popcorn. A layer of till 50-100 feet thick covers Paleozoic bedrock eroded flat by glacial activity. Humans have artificially flattened the landscape further by removing trees and tilling the area to a uniform elevation for agricultural activity.
As you leave Indianapolis and drive north to Lafayette or Fort Wayne, you will notice something very un-striking about the landscape: its flatness. In fact, the highest points within view in this part of the state are often interstate overpasses! So why the flatness? Why not rolling hills like Bloomington or Brown County? The reason lies in glacial activity, or the movement of ice across this landscape about 10,000+ years ago. This module and activity will introduce you to glacial geology and explore the remnants of the last Ice Age in Indiana.
Reading
BEFORE continuing this overview, please read the following pages in your lab book:
Pages 197-199: Please read all of this text to familiarize yourself with continental glaciation processes and landforms. You will investigate these processes and landforms in your activities for this lab.
Page 205: Read the introduction to this section to understand what a glacier and how glaciers have changed over geologic time.
Page 210: Read the information under Glacial Mass Balance to understand how scientists determine whether a glacier is advancing or retreating.
Page 216: Read this page to review the landforms associated with continental glaciation.
Glaciers
A glacier is a moving body of ice that forms on land from the accumulation and compaction of snow. Glacier formation begins when accumulated snow is compacted until most of the air pockets between the snow crystals are gone. Glaciers form and grow when accumulations of snow exceed melting during summer months. We don’t have glaciers in Indiana today, because on average our summer temperatures are way above freezing. Glaciers move by internal deformation, or flow. This is similar to squirting toothpaste on an angled surface, it will gradually move down the surface the more you squeeze out. With glaciers, the weight of snow and ice in the accumulation zone forces the ice to move downhill.
Glaciers can be classified as alpine or continental. Alpine glaciers occur in mountainous regions, you have probably seen these if you have visited Glacier National Park or Mount Rainier. Alpine glaciers are relatively small and are confined to valleys surrounded by bedrock highlands. In contrast, a continental glacier is one that covers a very large area and is generally unconfined. The ice sheet over modern Greenland is an example of a continental glacier.