GLACIAL EROSION: CHARACTERISTICS, TYPES, PRODUCTS, CONSEQUENCES, EXAMPLES - ENVIRONMENT - 2025

The glacial erosion is the wearing and modifications of the land area caused by pressure and movement of the masses of glacier ice. This type of erosion is possible thanks to the properties of water, especially its ability to solidify and fuse at room temperature.

Glaciers are huge masses of ice that with their weight and displacement produce various erosive effects. These include glacial skidding or rock chipping and skidding, as well as glacial abrasion or rock polishing.

Glacial erosion. Source:

Other effects of glacial erosion is the abrasion that causes the so-called glacial striae or fine channels carved into the rocky bottom. Dragging, on the other hand, also causes a modeling effect, for example in the creation of fields of hills or drumlins.

The different cuts, breaks and abrasions produced by the glacier's flow over thousands of years, substantially modify the landscape. Among the geomorphological formations that are formed as a result of glacial erosion are glacial valleys and glacial lakes. Like the muddy rocks, the fields of hills and other configurations of the relief.

characteristics

- Snow

Snow is a granular material (flakes) made up of small ice crystals that fail to aggregate into totally solid blocks. This produces a material with a certain density, but malleable and susceptible to compaction.

Formation and erosive effect

Snow forms in the atmosphere when water vapor condenses at temperatures below 0 ° C and then precipitates. This forms the snowfalls that deposit layers of snow on the ground.

The accumulation of layers with physical differences of greater or lesser compaction can cause displacements when they occur on steep slopes. This characteristic is important to understand both snow avalanches and the erosive effect of slow movements.

- The ice

Pure water subjected to an atmosphere of pressure and 0 ºC becomes a solid state and is called ice. However, water in nature contains impurities (minerals, organic acids), which is why it freezes at temperatures below 0 ºC.

On the other hand, in the high mountains the atmospheric pressure is lower, which also helps to lower the freezing threshold of the water.

Density

Water expands when it freezes and therefore increases its volume and decreases its density when it solidifies as ice. This property is relevant in erosive action, since the water penetrates through tiny cracks in the rocks and when it freezes it expands.

Therefore, in the summer thawing and winter freezing processes, expansive pressures are generated inside the rock formations. These pressures further crack the rocks and eventually break them.

Blue ice or glacial ice

Blue ice in Antarctica. Source: Joe Mastroianni, National Science Foundation

In a glacier, as layers of snow accumulate, the lower layers turn to ice and become more and more compacted. The snow in the upper layer has a density close to 0.1 and a porosity of 95% and in the lower layer the density is 0.92 and zero porosity.

The basal layers become so compacted that one meter of snow forms one centimeter of glacial ice or blue ice.

In this process, the air bubbles trapped in the ice are expelled, leaving a very clear ice. When this ice is exposed to sunlight, it absorbs the spectrum of red and reflects blue, hence the name blue ice.

Tempered ice and cold ice

Tempered ice is one that is close to the melting temperature while cold ice is at a temperature lower than that required for it to melt.

Ice movement

Generally speaking, ice is a brittle solid, but in layers thicker than 50 m it behaves like a plastic material. Therefore, the low adhesion between the different layers causes movement to be generated between them.

- Glaciers

They are large masses of ice and permanent snow that form in the polar regions or in high mountain ranges of the planet. The snow accumulates and compacts, forming increasingly dense ice and moves on the slopes with a strong erosive effect.

Mass balance

Matanuska Glacier in Alaska (United States). Source: Sbork

Normally a glacier has an area where it gains mass due to snowfall or freezing of liquid water, called an accumulation zone. As well as it also has an area where it loses water by landslides or sublimation, called the ablation zone.

A glacier is in a permanent exchange of mass and energy with the surrounding environment, losing and gaining mass in the process. The new precipitation adds layers of snow that will compact, increasing the volume of the glacier.

On the other hand, the ice loses mass when sublimated in water vapor and the glacier can suffer detachment of ice blocks. For example, in the case of coastal glaciers or sea ice that form icebergs.

Glacial movement

The weak molecular bonds between ice sheets cause movements between them, driven by the force of gravity when sloping. Furthermore, the adhesion of glacial ice to the rocky substrate is weak and enhanced by the lubricating effect of meltwater.

Because of this, the mass of the glacier moves downhill very slowly, at the rate of 10 to 100 meters per year. The speed is lower in the layer in contact with the ground due to friction, while the upper layers move at a higher speed.

Types of glaciers

Although there are various criteria for classifying glaciers, their classification by location and extent is highlighted here.

Continental cap glacier

These are large masses of ice that cover extensive continental areas, for example the glaciers of Antarctica and Greenland. They reach their greatest thickness in the center and their margins are much thinner.

Cap glacier

They are layers of ice covering mountain ranges or ancient volcanoes and, like the continental ice caps, these were more abundant in the geological past.

Mountain glaciers

It is the typical glacier that develops forming a U-shaped valley, presenting a glacial cirque at its head, tongue and glacier front. The parts of a mountain glacier are:

Circus

It consists of a depression surrounded by mountains that forms the glacier accumulation zone where the formation of glacial ice occurs.

Language

Glacier tongue. Source: NASA / Michael Studinger

It is the mass of ice and snow that advances following the direction of the slope of the valley, eroding it in a U-shape. The moving mass is shedding and dragging rock fragments, in addition to polishing the surface of exposed rocks.

Glacier front

It is literally the outpost of the glacier, at the front end of which it deposits part of the dragged materials constituting the frontal moraine.

Types of glacial erosion

Glacial erosion occurs due to the weight and movement of the glacier that generates thrust and friction forces.

Glacier start

Thanks to the thrust of the great moving glacier mass, fragments of rocks and whole rocks are dislodged and carried away. Glacial start is facilitated by gelling or gelling as water penetrates into cracks and freezes, increasing in volume.

In this way it acts as a lever that cracks the rock, releasing fragments that are then dragged away.

Glacial abrasion

The friction of dragged ice crystals and rock fragments acts like the action of a sandpaper or file when moving over the rocky surface. In such a way that they wear and polish, modeling the terrain in various characteristic ways.

Meltwater erosion

The glacial meltwater runs both inside the glacier and outside, generating erosion. Among the formations that have their origin in the erosive action of glacial water are the esker and the kettler or giant kettles.

Products of glacial erosion

Glacial valleys

The accumulation of snow at the head of a high altitude intramontane valley gives rise to the formation of a glacial valley. For this to be the case, the valley must be at an altitude above the limit of perpetual snow

The successive layers of snow compress the lower layers that end up crystallizing as glacial ice. Then the ice begins its movement in the direction of the slope carried by the force of gravity.

This moving mass erodes the ground as it passes, that is to say, detaching fragments and polishing rocks. Given the mass and its strength, acting for thousands of years, it ends up carving a valley whose cross section is U-shaped.

Suspended valleys

In the high mountains above the level of perpetual snow, glaciers are formed on the different slopes. Depending on the conformation of the mountain range, two glacial valleys can intersect transversely.

When this occurs, the major glacier will cut across the front of the minor glacier and continue its erosive work, resulting in a minor glacier valley leading to a cliff.

Glacial cirques

The effect of glacial erosion at the head of the valley gives a peculiar geomorphological conformation, with a more or less circular depression surrounded by vertical walls. This is called the glacial cirque and remains as evidence of ancient glaciers now gone.

Glacial striae

In some cases the abrasive action of ice and bottom moraine carves the valley surface with grooves or channels.

Muddy rocks

As the glacier passes, those rocks that due to their dimensions or roots manage to stay on the ground, are subjected to a polishing process. This models them as rounded rocks with a very smooth surface that protrude from the earth's surface, called mud rocks.

Moraines

Moraines. Source: The Photographer

A glacier carries with it fragments of rock of different sizes (tills), sand and mud that it ends up depositing, this set is called moraine. The moraines are classified into lateral, bottom and frontal, depending on the area of ​​the glacier that carries them.

Glacial lakes

Glacial erosion gives rise to glacial lagoons by generating depressions in the land where meltwater accumulates. These lagoons can be in the cirque of a disappeared glacier or in the terminal part of the glacial valley.

In the latter case, when the glacier disappears, the terminal moraine blocks the valley outlet like a dike, forming a lagoon. In this video you can see a glacial lake in Iceland:

Hilly fields o

In particular conditions, generally on flat terrain with low slopes and with previous debris, the glacier models a hilly landscape. They are small hills with a tapered (aerodynamic) shape, with a wide front facing the direction of origin of the glacier and narrow towards the rear.

Edges and

In those cases where there are two or more adjacent cirques around a mountain, the erosive action generates slopes with steep and sharp edges. If two glacial tongues run parallel to each other separated by a mountain slope, sharp rows are formed called ridges.

The Horns are peaks formed by the confluence in their environment of several glacial cirques that are eroding it around. As they wear down the bottom and carve the stone around it, the peak grows taller and sharper.

Esker

Melt rivers can flow under the glacier, carrying debris, while the river sides are depressed by the weight of the ice. As the glacier disappears, a long ridge of debris remains, to which other sediments are added.

Over time, the weathering of the rock and the deposited sediments form soil and vegetation grows. It forms an elongated and narrow hill landscape that has been used on many occasions to build roads or highways.

Kame

They are hills of irregular shape that are formed by accumulation of gravel and sand from ancient glaciers. Once the glacier has disappeared, the material consolidates and the weathering and sedimentation forms soil, growing grass and other plants.

Kettle

In some cases, large holes are produced on the surface of the glacier where the meltwater precipitates (glacial mill). Upon reaching the rocky bed, the water pierces it, forming circular depressions in the shape of a pot or kettle.

Consequences

Glacial erosion is a silent force that year after year deeply shapes the landscape.

Land transformation

The erosive force of a glacier acting over long periods of time, radically transforms the terrain. In this process it creates deep valleys and very steep and sharp mountain ranges, as well as the various characteristic geological structures.

Loss of soil

The force of the dragging of the glacial tongue causes the entire soil of the displacement area to disappear. In this sense, the areas of ancient glaciers present substrates with outcrop of the mother rock, with practically no soil.

Sediment load in rivers and lakes

Glacial erosion involves the dragging of sediments by the moving ice mass as the ice melts. This forms water currents that carry sediments to rivers and lakes of glacial origin.

Examples

Suspended valleys

In the Sierra Nevada de Mérida (Venezuela) is the Cascada del Sol, formed by the precipitation of meltwater from Pico Bolívar. The water runs through a small glacial valley called the Cañada de Las Nieves.

This valley was cut through the much deeper main glacial valley (100 m) on its way, forming the precipice of the waterfall. In the Andes mountain range, these suspended valleys and the waterfalls that are generated in them are common.

Norwegian fjords

Norwegian Fjord. Source: Ximonic (Simo Räsänen)

The famous fjords of Norway are gulfs in the form of long arms of the sea that penetrate inland between rugged mountains. These geological formations originated in the Quaternary due to the erosive action of glaciers that excavated the rock.

Later, when the glaciers disappeared, the depressions were invaded by the sea. There are also fjords in Chilean Patagonia, in Greenland, Scotland, New Zealand, Canada (Newfoundland and British Columbia), the United States (Alaska), Iceland and Russia.

Post glacier landscape in Wisconsin (United States)

Much of the North American territory was covered by ice caps 25,000 years ago, the so-called Laurentian Ice Sheet. This glacier left its mark on the configuration of the landscape in large areas, such as in the state of Wisconsin.

In this one there are moraine fields such as the Johnstown or Milton Moraine. Also kettles or giant kettles, glacial lakes and wide fields of hills or drumlins.

As you travel the interstate between Madison and Milwaukee, you can see a field with more than 5,000 drumlins. Over the millennia these hills have consolidated, forming soil and developing certain herbaceous vegetation.

References

1. Boulton, GS (1979). Processes of Glacier Erosion on Different Substrata. Journal of Glaciology.
2. Boulton, GS (1982) Processes and Patterns of Glacial Erosion. In: Coates, DR (ed.). Glacial Geomorphology. Springer, Dordrecht.
3. GAPHAZ (2017). Glacier and Permafrost Hazard Assessment in Mountain Regions - Technical Guidance Document. Prepared by Allen, S., Frey, H., Huggel, C. et al. Permanent Working Group on Glacial Hazards and Permafrost in High Mountains (GAPHAZ).
4. Nichols, G. Sedimetology and estratrigraphy. 2nd edition. Edit Wiley-Blackwell.
5. Mickelson, DM (2007). Landscapes of Dane County, Wisconsin. Wisconsin Geological and Natural History Survey.
6. Yuen, DA, Sabadini, RCA, Gasperini, P. and Boschi, E. (1986). On transient rheology and glacial isostasy. Journal of Geophysical Research.