Glacial Geology Overview

Glacial geology is important in Illinois' most recent geologic past, the Quaternary Period (also called the Ice Age), during which continental glaciers repeatedly plowed across the state eroding and redistributing material and creating new landforms. Today, Illinois is experiencing an interglacial episode, a relatively quiescent and warm interval of the Quaternary Period that allows the soil to form and crops to grow. Quaternary geology encompasses both the cold and warm intervals and the glacial and nonglacial processes of the past 2 million years.

Why We Study Glacial and Quaternary Geology

The landscape of Illinois is the product of its most recent past, the Quaternary Period, roughly the last 2 to 2.5 million years. This period of geologic time, in which we live today, has been characterized by alternating glacial and interglacial episodes reflecting Earth's climate flip-flops between cooler and warmer intervals. During the Quaternary Period, over 90% of Illinois was glaciated, and the remaining 10% of the state was affected by glacier meltwater, dust storms, and a climate more frigid than that of today.

Even though in terms of geologic time these Quaternary glacial episodes were relatively short-lived, their impact on Illinois' landscape, natural environment, and economy cannot be overemphasized. The glaciers delivered new geologic materials to Illinois providing a rich base for soil, water, and plant and animal communities-resources that nurture life and sustain society. These materials, up to 500 feet thick and averaging about 100 feet thick across the glaciated part of Illinois, are those on which we live-construct our buildings, grow our crops, pump much of our drinking water, extract sand, gravel, and fill for our roads, and bury our trash. Their variation enriches the diversity of the forests, prairies, and wildlife habitats we enjoy. These materials flesh out the bedrock surface, creating a smoother and more undulating topography that tells the story of Illinois' most recent geologic past.

Because the Quaternary materials on which we reside are at the same time both a vital and vulnerable part of the well-being of Illinois residents, mapping their distribution and characterizing their properties so that we can wisely use and protect them is an important part of the Survey's mission. The Quaternary Geology Section was created to study and map these earth materials.

Maximum Extent of Glacier Ice in North America

Today glacier ice covers about 10% of Earth's land surface, but in the recent geologic past, it covered over 30% of Earth's land surface. The photo above shows the maximum extent of glacier ice in North America during the last glacial maximum about 20,000 radiocarbon years ago. The globe is on display at the Visitor's Center for the Chippewa Moraine Ice Age National Scientific Reserve, New Auburn, WI.