Glaciated Landscapes

Active glaciated landscapes

A glacier is a huge mass of ice (usually found in highlands), and it generally falls into two broad categories: alpine glaciers and ice sheets. Both types of glaciers broadly form in the same way. Over many years, the accumulation of snowfall exceeds the rates of ablation. The long-term net positive accumulation of snow causes it to compact as a result of high pressure on its base layers, which is caused by the weight of the upper layers of snow. Compaction occurs when the pressure on the ice forces air out of the snow layers.

When enough air is pushed out, meaning that air makes up 50% of the volume between the snow crystals, the snow forms into granular ice. The next stages of compaction lead to the formation of firn (approximately 25% air), followed by glacial ice (approximately 20% air). The reduction of air between the snow/ice crystals increases the density of the materials, causing the change from snow to granular ice to firn to glacial ice.

What is the difference between a glacier and an ice sheet?

The difference between alpine glaciers and ice sheets relates to the locations in which they form and their directions of travel.

Alpine glaciers

Alpine glaciers form on mountainsides, usually within a corrie (also known as a cirque). When they escape these hollows, they traverse down valleys. The accumulation of ice follows the same pattern mentioned above.

After a long period of accumulation and compaction, an increase in pressure in the body of ice may cause the development of meltwater in its base. Alongside the shape of the hollow and the weight of the ice mass, the lubrication caused by the meltwater sets off a process called rotational slip. The glacier begins moving in a circular motion. Due to this motion, there is a chance of the glacier escaping the corrie/cirque hollow. It would then start traversing down the valley in which it is located.

This process is discussed in depth in Erosional Landforms.

Ice sheets

Ice sheets are not limited to mountainsides or valleys. Unlike alpine glaciers, they do not necessarily form within hollows but rather anywhere with high accumulation potential. As the accumulation of snow is not bound by any landscape, ice sheets generally begin as broad domes spreading out in all directions. As the sheet begins to move, it will cover the environment in a large blanket of ice. At their largest extent, these sheets are known as continental glaciers.

What is a glacial system?

By exploring these features and how they relate to one another, we can understand the underlying reasons why glaciated landscapes function the way they do and how their landforms form the landscape as a whole.

Inputs

These inputs may also enter via avalanches or by wind blowing them in from other landscapes.

Transfers

An example is the movement of the ice mass due to gravity and the landscape’s gradient, which is accelerated by an increase in accumulation at the source of the glacier. This process of transportation is largely behind glacial effects on the landscape.

The glacier's movement erodes the valley in which it resides by a mixture of quarrying, abrasion, and fluvioglacial erosion. These will change V-shaped valleys into U-shaped valleys and form distinct landscapes such as drumlin fields, moraines, etc. This is discussed further in Glacial Landforms.

Stores

This store will vary in size according to the number of inputs, also known as accumulation, and the number of outputs, also known as ablation. Meltwater may also be considered as a store when connected to the glacial mass, for example, supraglacial lakes or perhaps subglacial streams.

Outputs

A more large-scale output is ice calving. This occurs when the part of a glacier that moves out into a body of water breaks off from its snout. It may also occur when a glacier hangs off a valley’s edge, but this is not as common.

How is a glaciated landscape formed?

Glaciers begin forming in areas where snow can accumulate at a greater rate than it melts. Soon after falling, the snow compresses under pressure and becomes denser and more tightly packed. It changes from light crystals to hard, round ice. This process repeats until the snow is compacted into glacial firn, which is a process known as firnification.

Following a long process of firnification, the ice will thicken and accumulate a large mass. This large mass of ice begins to move under its own weight and exerts a significant amount of pressure, causing the firn to melt despite a lack of increase in temperature. The increased meltwater decreases the friction between the base and the ice mass, allowing the ice to escape the hollow in which it has formed. This accumulated body of ice is known as a glacier.

Gravity pulls the glacier down and allows it to advance. As it does so, the numerous processes that shape a glacial landscape occur and begin shaping the landscape.

Over the course of many years, a distinct glacial landscape will form as a result of these glacial processes. Even if a glacier fully retreats and is no longer present, the landscape is permanently changed.

Some examples of glaciated landscapes

The Mer De Glac glacier, located on the northern slopes of the Mont Blanc Massif in the French Alps, is an example of an active glaciated landscape. The Mer De Glac is continuously retreating as a result of increasing temperatures in Europe, attributed mainly to global warming. Active glacial landscapes are very important because they help us understand the landforms we see in relic glacial landscapes.

An example of a relict glacial landscape is the Lake District, located in Cumbria in northern England. This area is characterised by numerous post-glacial landforms such as drumlins in the Vale of Eden, glacial lakes known locally as tarns, and ribbon lakes such as Lake Windermere.

Innominate Tarn in the Lake District, UK, Pixabay

Many of these post-glacial landscapes, especially ribbon lakes and tarns, serve as tourist attractions. Millions of visitors come to the Lake District each year.