Glacial Landforms and How to Read Them on a Walk

For long stretches of the Pleistocene, ice covered vast areas of North America, northern Europe and Asia. When the glaciers finally withdrew, they left a signature on the land that is still legible today. Once you learn the vocabulary of glacial landforms, whole regions read like a book about the last Ice Age.

Forms carved by ice

Glaciers are erosive engines. As they flow, they grind, pluck and polish the rock beneath them, leaving characteristic shapes:

• Cirques — bowl-shaped hollows high on mountainsides where a glacier was born.
• U-shaped valleys — broad, steep-walled troughs, unlike the V-shaped valleys of rivers.
• Arêtes and horns — knife-edged ridges and sharp peaks left where cirques cut back to back.
• Striations — parallel scratches on bedrock, showing the direction the ice moved.

Forms built by ice

Glaciers also carry enormous loads of rock and sediment, and where they melt they set that material down. These depositional landforms are just as diagnostic:

• Moraines — ridges of unsorted debris marking a glacier's edges or its farthest advance.
• Erratics — isolated boulders transported far from their source and stranded on unfamiliar ground.
• Drumlins — streamlined, whale-backed hills shaped beneath moving ice.
• Kettles — ponds or hollows left where a buried block of ice melted away.

Putting it together in the field

On a single walk in glaciated country you can often trace the whole story. Start in a high cirque, follow a U-shaped valley downstream, notice the striations on a polished outcrop, and end at a moraine that marks where the ice finally stopped. Each feature is a sentence; together they describe the advance and retreat of a glacier that vanished thousands of years ago.

The Pleistocene underfoot

Much of the terrain we treat as timeless — a lakeside, a rolling hill, a scatter of boulders in a field — is in fact very young and very specific, the direct handiwork of Ice Age glaciers. Reading these landforms is one of the most direct ways to feel the reach of the Pleistocene into the present day.