Landscape near Hilly Grove on Manitoulin Island

(Photo: Landscape around Hilly Grove, Manitoulin Island. Photo by Vanessa Farnsworth.)

Located in Lake Huron, Manitoulin Island has a complex geologic history that dates back billions of years.

The island is part of the Canadian Shield, one of the oldest and most stable geological regions in the world and was formed over a billion years ago by a combination of volcanic activity and tectonic shifts that led to the creation of ancient granite and gneiss rocks that together form the island's foundation.

During the Paleozoic era (540 to 250 million years ago), Manitoulin lay beneath a shallow sea and, as the centuries passed, sedimentation began to form a thick layer of limestone and dolomite, which gave rise to some of the island's most spectacular rock formations. These sedimentary rocks offer a glimpse into the region's ancient past, allowing us to see evidence of the marine life that once flourished in that long vanished sea.

Fast forward to the Mesozoic era (250 to 66 million years ago) and much of the overlying sedimentary rock had eroded, exposing older Precambrian rocks, which remain visible as outcrops and cliffs throughout the island. Later, during the last ice age, the island was covered by glaciers, which carved out the many lakes, rivers, and valleys that dot the landscape. When those glaciers melted, many caves and sinkholes were created that can be explored to this day.

Occasional earthquakes and other geologic events have continued to shape Manitoulin's landscape. The island's many hiking trails and natural areas provide opportunities to explore the island's geologic history. From the ancient Precambrian rocks to the towering limestone cliffs and the glacially carved landscapes, Manitoulin Island offers a unique and fascinating glimpse into northern Ontario's geologic history.