The Geological Story of Pinhook Bog

Thousands of years ago, mighty glaciers advanced and receded across the Midwest. They carved the rolling hills of moraines, ground stone into sand, and eventually melted and formed the great lakes. Pinhook Bog was formed when a piece of these icy giants broke free and melted right here in what is today northwest Indiana. Its waters created a lake whose bed was sealed tightly with clay-like “glacial till,” the sediment left behind by the receding glaciers. With no springs, rivers, or streams to replenish the lake, rainfall or melting snow became the only available sources of fresh water. In these stagnant conditions, organic matter decomposed here over thousands of years and slowly filled the lake, depleting the oxygen and making the water highly acidic. This in turn slowed the process of decay and rendered the bog a prehistoric time capsule, preserving pollen and other relics deep in these murky waters. In time, the bog will fill completely and become solid ground.