Glacial deposition creates a wide variety of landforms, from massive ridges of rocky debris to gently rolling plains of sediment. The most well-known is the moraine, a mound or ridge of material carried and dropped by a glacier as it moves or melts. But moraines are just one member of a larger family that includes drumlins, eskers, kames, outwash plains, till plains, and kettle lakes.
These landforms fall into two broad categories: those deposited directly by ice and those shaped by glacial meltwater. The distinction matters because it determines the type of sediment left behind and the shape of the resulting landscape.
Moraines: Ridges of Glacial Debris
Moraines are the most recognizable landforms created by glacial deposition. They form when a glacier transports rock, soil, and other debris and then drops that material as the ice melts. The result is a ridge or mound of unsorted sediment that can stretch for miles.
There are several types, each named for where the debris accumulates. Lateral moraines are sharp-crested piles of rock and debris along the sides of a glacier. They form only in the ablation zone, where more ice melts each year than accumulates as snow. Terminal moraines mark the farthest point a glacier reached before retreating, creating a curved ridge across the landscape. Ground moraines are broad, gently rolling sheets of till left behind as a glacier retreats more evenly.
Medial moraines form where two glaciers merge, combining their lateral moraines into a single dark stripe running down the center of the joined ice flow. These are mostly thin, surface-level features, which is why they rarely survive intact after the ice fully retreats. You can see well-preserved lateral moraines in places like Glacier National Park, where they stand as steep, narrow ridges flanking former glacier valleys.
Drumlins: Streamlined Hills Beneath the Ice
Drumlins are elongated, teardrop-shaped hills that form beneath a moving glacier. They typically appear in clusters called drumlin fields, with the tapered end pointing in the direction the ice was flowing. A single drumlin can be a few hundred meters long and tens of meters tall.
How drumlins form is still debated among geologists. Research examining dozens of drumlins has identified a continuum of formation processes. Some are depositional, built up when sediment flows into low-pressure zones behind obstacles under the ice. Others are deformational, shaped when the glacier’s weight and movement reshapes weaker sediment beneath it through compression and stretching. Still others are erosional, left behind when surrounding material is stripped away. Many drumlins have a rock core with deposited sediment molded around it. The common thread is that they all form at the boundary between the glacier’s base and the ground beneath it.
Glacial Till vs. Sorted Sediment
The material a glacier deposits directly is called till, and it has a distinctive characteristic: it is completely unsorted. Till contains particles of every size, from massive boulders down to fine clay, all jumbled together. That’s because a glacier simply picks up whatever lies in its path and drops it in place when the ice melts, with no running water to sort or organize the material.
This is the key difference between landforms deposited by ice and those deposited by meltwater. When glacial meltwater carries sediment, it sorts particles by size the way any river does. Heavier material like gravel settles out first, closer to the glacier, while finer sand and silt travel farther downstream. Till plains, broad flat areas covered in unsorted till, look and feel very different from outwash plains, even though both owe their existence to the same glacier.
Eskers and Kames: Meltwater Deposits
Not all glacial depositional landforms come from ice dropping its load directly. Meltwater flowing through and beneath glaciers creates its own distinct features.
Eskers are long, winding ridges of sand and gravel that formed inside tunnels within or beneath a glacier. Picture a river running through an ice tunnel: as sediment settles on the tunnel floor, it builds up a raised bed. When the glacier finally melts away, that raised bed remains as a sinuous ridge snaking across the landscape. Eskers can be straight or tortuous, with sharp, uneven crests. Their internal structure typically shows alternating layers of coarse gravel, fine gravel, and sand, with the sandy portions being well sorted. In studied examples, roughly 80 percent of sand grains fell within a narrow size range, showing how effectively flowing water organizes sediment by weight.
Kames are rounded or pointed mounds rather than ridges. They form when meltwater deposits sediment in depressions on or against the glacier surface. Like eskers, kames are composed mainly of sand and gravel, but their internal layering is distinctive. The layers dip in various directions, reflecting how sediment accumulated on sloping surfaces from multiple angles as the ice shifted around them. This chaotic layering pattern is unique to kames and helps geologists distinguish them from other glacial features.
Outwash Plains: Broad Sediment Aprons
Beyond the glacier’s edge, meltwater fans out across the landscape and deposits vast sheets of sorted sediment called outwash plains (also known by the Icelandic term “sandur”). These are built by braided river systems, networks of shallow, shifting channels that spread sediment over a wide area.
Iceland’s Skeiðarársandur is the largest active outwash plain on Earth, covering 1,350 square kilometers. Three major braided stream systems channel water and sediment from an outlet glacier onto the plain. Within a few kilometers of the ice front, the channels merge and split repeatedly, and farther out the flow transforms into a shallow, discontinuous sheet of water. The result is a gently sloping plain of gravel and sand that gets progressively finer with distance from the glacier, as heavier particles drop out first and lighter ones travel farther.
Outwash plains are essentially massive alluvial fans powered by glacial meltwater rather than rainfall. Their layered, sorted sediment makes them geologically distinct from the unsorted till plains deposited directly by ice.
Kettle Lakes: Holes Left by Dead Ice
Kettle lakes form through a combination of deposition and melting. When a glacier retreats, blocks of stagnant ice sometimes break off and become partially or fully buried in sediment. These buried ice blocks can persist for years or decades, insulated by the debris around them. When they finally melt, they leave behind a depression in the sediment surface. If that pit fills with water, it becomes a kettle lake.
Kettles are common on outwash plains and in areas of ground moraine. They range from small ponds a few meters across to lakes spanning several kilometers. Walden Pond in Massachusetts is a famous example. The shape and depth of a kettle depends on the size of the original ice block and how deeply it was buried before melting.
How These Landforms Relate to Each Other
In any landscape shaped by glaciers, these features tend to appear together in a predictable spatial pattern. Drumlins and till plains occupy the zone where ice once covered the ground. Moraines mark the glacier’s edges and its farthest advance. Beyond the terminal moraine, outwash plains spread outward, built by meltwater that flowed away from the retreating ice. Eskers trace the paths of former meltwater tunnels beneath the glacier, while kames dot the surface where pockets of sediment accumulated in and around stagnant ice. Kettles punctuate outwash plains and moraine fields wherever buried ice blocks melted away.
Together, these landforms create a readable record of where a glacier existed, how far it extended, and how it behaved as it retreated. Much of the upper Midwest of the United States, Scandinavia, and the British Isles are blanketed in these features from the last ice age, shaping everything from local drainage patterns to the fertility of agricultural soils.