Introduction to glacial landforms

Glaciers are one of the most powerful forces shaping our local landscape. As glaciers flow downhill from mountains to the lowlands, they erode, transport, and deposit materials, forming a great array of glacial landforms. They can erode mountains, and change their morphology. Large glaciers and ice sheets can deposit great swathes of sands and gravels, forming swarms of hills called drumlins. Ice sheets deposit great thicknesses of glacial tills, and glaciers and ice sheets form moraines at their terminus. These pages will explain these concepts in more detail.

Erosional glacial landforms

In their upper reaches, glaciers can erode bedrock by quarrying, pucking, abrasion and polish. Rocks and debris embedded in the ice scratches the rock below.

Polished and striated bedrock in Utah. Photo credit: Bethan Davies

The photograph below shows ice-scoured, smoothed bedrock in Greenland. The passage of the ice, with lots of debris embedded in it, has scratched and abraded the rocks, making them smooth. Over time, roche moutonnees develop, which are smooth on one side but have a blunted downstream face.

Bethan Davies standing on ice-scoured bedrock in Greenland. She is pointing in the direction of former ice flow.
Polished and striated bedrock in Utah. Note the plucked face on the down-stream end. Photo credit: Bethan Davies

This erosion creates deep hollows in mountain sides, called cirques. Multiple cirques on a mountain may cause a pyramidal peak as they form back-to-back. Cirques are one of the most visual and characteristic glacial landforms of glaciated mountains.

Classic glacial cirque basin. Cwm Clyd in the Glyderau mountains of Snowdonia. Image from GoogleEarth.

Larger glaciers can excavate a glacial trough, which has a parabolic, or U-shape.

The parabolic glaciated valley of Glen Coe, Scotland. Photo credit: Bethan Davies

Trimlines on the valley side mark out the former ice surface. The area below the trimline was smoothed by the passage of glacier ice. In the photo below, the trimline was formed during the “Little Ice Age”, when the glacier reached the moraines visible in the bottom of the photograph. The valley side above the trimline was not glaciated at this time, and so is more vegetated and weathered.

Valley side trimlines (labelled with white arrows) marking the former thickness of the Callequeo Glacier, Monte San Lorenzo. Photo credit: J. Martin.

Depositional glacial landforms

Lower down, in the ablation zone, deposition becomes more important and shear stress lessens. This can lead to the deposition of vast thicknesses of unsorted sediments called tills.

Two tills
Two tills rest on top of Magnesian Limestone bedrock at Whitburn Bay, overlain by deformed glaciofluvial sands (sands deposited by a proglacial river). Note the large, faceted boulders at the boundary between the two tills.

Around the margins of the glacier, lateral moraines may develop in the ablation zone, and terminal moraines may form at the end of the glacier. In front of the ice margin, there may be small scale streamlined ridges called flutes.

The ridges in the forefield of this glacier are moraines. They are made up of debris carried by the glacier, and deposited in ridges at its terminus.
Push moraines and flutes in a recently deglaciated glacier forefield.
Esmeralda Moraine. A subaerial terminal push moraine with symmetrical sides. Photo credit: Bethan Davies

Under larger ice masses such as ice sheets, drumlins may form. These are elongated hills made up of glacial sediments (sands, gravels, boulders, unsorted muds) that form in the direction of ice flow.

Drumlin at Holwick, Teesdale. Photo credit: Bethan Davies

Under faster-flowing ice streams, mega-scale glacial lineations may form. These landforms are important for telling us about directions and dynamics of ice flow under former ice sheets.

Belgica Trough Mega Scale Glacial Lineations, Antarctic Peninsula.

Glaciofluvial landforms

Glaciers are wet. Temperate glaciers, which are those in more moderate climates and that have meltwater at their base, produce huge volumes of water each melt season. This results in a characteristic suite of glaciofluvial landforms.

Meltwater stream on Mendenhall Glacier, Alaska. From: Gillfoto, Wikimedia Commons

All this water produces a whole suite of glacial landforms. These include eskers (ridges of sediments that form underneath a glacier), kame terraces, sandar (braided gravel-rich outwash streams), and meltwater channels.

A sinuous esker ridge, and several smaller eskers, mapped from satellite imagery in the Lago Cochrane-Pueyrredón valley. Copyright: J. Bendle.

Meltwater may cut meltwater channels underneath and around the margins of the glacier. Ice-marginal meltwater channels usually form around sub-polar glaciers where water cannot get underneath the glacier, which is frozen to its bed. They therefore form in a lateral position, between the glacier and the valley flank, or around the snout. These meltwater channels can therefore mark out the position of the former ice margin.

Lateral meltwater channel in Lunedale, Pennines. Image credit: Bethan Davies.

The glaciofluvial rivers that drain away from glaciers are typically very laden with sediment. If the valley floor is quite low-angle, as is common in glacial valleys, then the river tends to form a braided pattern, with bars of gravelley sand forming. These rivers are very active and their form changes regularly. These features are called sandars.

Glaciofluvial outwash from Nef Glacier, Patagonia

Glaciolacustrine landforms

Many temperate glaciers terminate in glacial lakes, which results again in a characteristic suite of glacial landforms. Lakes may form in front of glaciers, occupying the glacial overdeepening, and may be dammed by moraines, by the ice itself, or by bedrock.

An ice-dammed lake on the northern margin of the Russell Glacier, in western Greenland.

Moraine-dammed and ice-dammed lakes may be susceptible to hazardous Glacial Lake Outburst Floods.

Rapid growth of glacial lakes in the Bhutan-Himalaya in response to retreating glacier termini. Photo: NASA/USGS, Wikimedia Commons.

Sediments in glacial lakes may be varved, with winter and summer layers being laid down each year.

Varves in a glacial lake. Photo credit: Jacob Bendle.

The location of former glacial lakes may be marked out by shorelines, raised deltas, beaches, and grounding line fans or morainal banks.

Raised delta in Patagonia. The high flat delta top formed when the lake was higher, due to ice damming the outflow. The lower delta is forming in the lake today.

Glacial landsystems

The types of glacial landforms that are generated are particular to glacier flow, basal processes, the substrate (soft and deformable? Hard crystalline bedrock?), the basal driving stress and thermal regime, and the ice temperature.

There are diagnostic landforms associated with wet-based sheet flow, ice streams, and surging ice. These diagnostic suites of landforms are called glacial landsystems.

Ice streamsSurging ice Sheet flow Cold-based ice
Mega scale glacial lineations (MSGLs)Looped medial morainesMarginal / subglacial / glaciofluvial domainsMay be very little modification of previous landforms
Progressive elongation of landforms down-iceThrusted end morainesPush, dump, squeeze morainesSmall glaciotectonic structures
Trough mouth fansConcertina eskersSubglacial till, flutes, drumlins, overridden morainesSome deposits with a coarse, sandy to boulder-gravel texture.
Till, glaciotectonised sedimentsTill, glaciotectonite, complex till stratigraphiesRoche moutonnees, striated and polished bedrockLittle evidence of fluvial reworking, but aeolian reworking may be common.
Drumlins, meltwater channels, terminal moraines, grounding linesCrevasse-squeeze ridges; flutingsTill, glaciotectonite 
“Sticky spots” (bedrock bumps/cold-based ice/dry bed)Hummocky moraineSandur, eskers, kame terraces,  proglacial lakes, braided channels, pitted outwash 

In these pages, you can learn more about glacier erosional and depositional landforms. There are case studies to illustrate the key points.

Once you have a grounding in the different kinds of glacial landform, take a look at the Glacial Landsystems pages, where the different suites of landforms that make up characteristic glacial landscapes are highlighted.

You can learn about the techniques that researchers use to understand these landforms, including geomorphological mapping and chronostratigraphy (dating glacial landforms).

There are sections of the website here on the characteristic landforms associated with the last Antarctic Ice Sheet, British-Irish Ice Sheet and the Patagonian Ice Sheet, and even glaciers on Mars.

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