Glaciers create some of the most dramatic landscapes on Earth, carving deep valleys, sharpening mountain peaks, and depositing vast fields of sediment as they advance and retreat. These landforms fall into two broad categories: those shaped by erosion (where the glacier removes rock) and those shaped by deposition (where the glacier leaves material behind). About 10 percent of Earth’s land surface is still covered by glacial ice today, but the landforms glaciers have left behind stretch across far more of the planet.
How Glaciers Shape the Land
Glaciers reshape terrain through two main processes. In abrasion, rocks and debris frozen into the base of the glacier scrape along the bedrock like sandpaper, polishing and gouging the surface beneath. In plucking, the glacier freezes onto cracked bedrock, and as it moves forward, it pulls chunks of rock loose and carries them along. Together, these processes allow glaciers to cut through solid rock over centuries.
Most glaciers move slowly, typically a few meters per year, though some extreme cases like the Jakobshavn Glacier in Greenland have been clocked at over 40 meters per day. Even at slow speeds, the sheer weight and persistence of glacial ice transforms landscapes on a massive scale. Two types of glaciers do this work: alpine glaciers, which form near mountaintops and flow downhill through valleys, and continental ice sheets, which spread across enormous areas near the poles. Each type leaves a distinct set of landforms behind.
Erosional Landforms in Mountains
Alpine glaciers produce the rugged, dramatic scenery people associate with places like the Alps, the Rockies, and the Himalayas. The process starts with a cirque, a bowl-shaped depression carved into a mountainside where snow accumulates and compresses into glacial ice. The glacier grinds the floor and walls of this bowl deeper and steeper over time, and when the ice eventually melts, it leaves behind an amphitheater-like hollow that often fills with water to form a mountain lake called a tarn.
When two cirques form on opposite sides of a ridge, both glaciers erode toward the center, leaving a narrow, knife-edged ridge of rock between them called an arête. If glacial erosion cuts all the way through the ridge, the low point that forms is called a col. When three or more cirques carve into a single peak from different directions, the remaining rock is sharpened into a steep, pyramid-shaped summit called a horn. The Matterhorn in Switzerland is the classic example.
U-Shaped Valleys and Hanging Valleys
Rivers cut narrow, V-shaped valleys. Glaciers take those same valleys and dramatically reshape them. As a glacier flows through a river valley, it erodes the entire floor and walls rather than just cutting a narrow channel at the bottom. It widens the floor and steepens the walls. After the glacier retreats, what remains is a broad, flat-bottomed, steep-walled U-shaped valley, sometimes called a glacial trough.
Smaller tributary glaciers feeding into a main valley glacier don’t carve as deeply as the larger one. When the ice melts, these smaller valleys are left perched high above the floor of the main valley, creating hanging valleys. Waterfalls often pour from hanging valleys down to the main valley floor. Yosemite’s famous waterfalls flow from hanging valleys carved during the last ice age.
Fjords
When a glacier carves a deep U-shaped valley all the way to the coast and the ice eventually retreats, seawater floods in to fill the trough. The result is a fjord: a long, narrow, steep-walled inlet. The depth of a fjord depends on the erosive power of the glacier that formed it, which is related to the glacier’s size and the type of bedrock it carved through. Norway’s Sognefjord, for instance, reaches depths of over 1,300 meters. The breadth of a fjord roughly corresponds to the width of the glacier that carved it.
Depositional Landforms
Glaciers don’t just remove rock. They also carry enormous amounts of debris, from fine silt to house-sized boulders, and deposit it as the ice slows or melts. This unsorted mix of sediment is called till. The landforms built from this material can stretch across huge areas, especially where continental ice sheets once covered the landscape.
Moraines
Moraines are accumulations of rock and debris transported and dropped by glaciers. They come in several varieties depending on where the debris ends up.
- Lateral moraines form along the sides of a glacier. As ice melts in the lower portion of the glacier, it drops sharp-crested ridges of debris that often remain visible on the landscape long after the ice is gone.
- Medial moraines form where two glaciers merge, trapping debris between them in a dark stripe running down the center of the combined ice flow. Because they sit on the glacier’s surface rather than being embedded deeply, medial moraines are rarely preserved after the ice retreats.
- Terminal moraines mark the farthest point a glacier reached before retreating. They form a ridge of debris across the full width of the glacier’s path.
- Ground moraines are continuous layers of till spread across the land beneath a steadily retreating glacier, creating gently rolling terrain.
Drumlins
Drumlins are teardrop-shaped hills that form beneath glaciers. They’re elongated in the direction the ice was moving, with a steeper slope on the side that faced the advancing glacier and a gentler tail on the downstream side. Because of this consistent shape, geologists use drumlins to map the direction ancient ice sheets flowed. Drumlins rarely appear alone. They tend to cluster in fields of dozens or hundreds, creating a landscape of smooth, oval hills. Parts of upstate New York and Ireland are covered in drumlin fields.
Eskers and Kames
Not all glacial deposits are dumped directly by ice. Meltwater flowing beneath or within a glacier carries sediment and deposits it in sorted layers, with larger particles settling first and finer material traveling farther. Eskers are long, winding ridges of sediment that trace the paths of rivers that once flowed through tunnels under or inside the glacier. They can stretch for kilometers across the landscape, looking like narrow, snaking railroad embankments.
Kames form differently. When meltwater washes sediment into a depression on the glacier’s surface, the debris collects in a pile. Once the surrounding ice melts, this mound of sorted gravel and sand is deposited on the ground as a steep-sided, conical hill.
Kettles
When a retreating glacier leaves behind large blocks of ice buried under layers of till, the buried ice slowly melts and the ground above it collapses into a shallow, bowl-shaped depression. These are kettles. When they fill with water, they become kettle lakes. Walden Pond in Massachusetts is a kettle lake, and much of the lake-dotted terrain across Minnesota and Wisconsin formed this way.
Outwash Plains and Loess
Beyond the terminal moraine, meltwater streams spread sediment across broad, flat areas called outwash plains. Because the sediment is carried by water rather than ice, it gets sorted by size as it travels: coarser gravel drops out first near the glacier, while finer sand and silt are carried farther away. This creates a gently sloping plain of layered sediment that can cover hundreds of square kilometers in front of a melting ice sheet.
The finest material from outwash plains gets picked up by wind and carried even farther. These wind-blown deposits of fine, yellowish-gray silt are called loess. After the last ice age, meltwater from retreating continental glaciers produced vast amounts of fine sediment that winds redistributed across the landscape. Loess deposits in the American Midwest and central China are tens of meters thick in places, creating some of the most fertile agricultural soil on Earth.
Alpine vs. Continental Landforms
The type of glacier determines which landforms dominate a landscape. Alpine glaciers produce the sharp, dramatic features of mountain terrain: cirques, arêtes, horns, U-shaped valleys, and fjords. These are erosional landforms shaped by ice flowing through narrow corridors with steep gradients.
Continental ice sheets, which spread across flat or gently rolling land, leave behind a different signature. Their landforms are primarily depositional: drumlins, eskers, moraines, outwash plains, kettle lakes, and thick layers of loess. The upper Midwest of the United States, much of northern Europe, and large parts of Canada owe their gently rolling terrain, rich soils, and thousands of lakes almost entirely to the work of ice sheets that retreated roughly 10,000 to 12,000 years ago.