Ontario is Getting Taller | SciShow

The Gist

The title promises to explain how Ontario is getting taller. The real answer is that ancient glaciers depressed the Earth's crust, and now that the ice is gone, the land is rebounding upward by 13 millimeters every year.

Quick Overview

Ontario is rising in elevation because of glacial isostatic rebound, a process where the Earth's crust springs back upward after the immense weight of the Laurentide Ice Sheet melts away. Ancient glaciers shaped the geography of North America and Europe by carving deep fjords, leaving behind massive beds of glacial till, depositing giant erratic boulders, and carving the Great Lakes. While Ontario rises, other regions like coastal areas and parts of the British Isles continue to sink as surrounding forebulges relax.

Key Points: About 27,000 years ago, ice sheets covered Canada, the United States, Iceland, and Scandinavia, fundamentally carving and changing the geology of the northern hemisphere. Fjords in Norway formed as ancient glaciers flowed down mountain valleys and carved steep U-shaped channels, leaving behind submerged valleys that plunge deep below sea level. Glacial till left behind by the Laurentide Ice Sheet created flat and fertile soil across the American Midwest rich in nutrients like phosphorus, potassium, and zinc. Large boulders called erratics were carried hundreds of kilometers away from their origins by glaciers and dropped in new locations, such as Waldo's Rock in Iowa. The Great Lakes and other water basins were carved out by the sheer weight of the Laurentide Ice Sheet and filled with meltwater when the ice retreated. Glacial isostatic rebound causes parts of Ontario, Canada, to rise by 13 millimeters every year as the land springs back from the weight of former ice sheets. The Driftless Area in Wisconsin escaped glacial coverage entirely because the high-elevation terrain forced the ice sheet to flow around it, leaving behind steep rocky bluffs.

Context: Glaciers have repeatedly advanced and retreated across North America and Europe, leaving behind a scarred and sculpted landscape that dictates modern agriculture, water systems, and topography. Understanding these ancient ice sheets explains why certain regions are flat, why massive boulders sit in random forests, and why the Earth's crust is still moving today.