Glacial System

A glacial system is the overarching categorisation of a glacier within a glaciated landscape. The boundaries between what is considered the glacial system and what is not are loosely defined; however, a common convention is to define the region that is in direct contact with the glacier as part of the glacial system.

Glacial system categorisation and diagram.

The glacial system consists of four main components: inputs, outputs, stores, and transfers. These components are common to most physical systems.

Fig. 1 - diagram of an alpine glacier

What are inputs?

Inputs refer to either physical matter or energy which enters the system from outside the boundaries of the system. These are objects which increase the glacier’s physical mass or movement. Some of these inputs may be snow, hail, or rain and some could argue that solar radiation should also be considered an input. The understanding of inputs into the glacial system is essential to understand the accumulative processes causing accumulation in a glacier’s mass balance (see mass balance).

What are outputs?

Outputs are defined as the physical matter or energy that exits the system, escaping the system’s boundaries. In the context of glaciers, these usually consist of meltwater run-off or the calving of large bodies of ice. These outputs are closely interlinked with the ablation of a glacier’s mass.

What are stores?

Stores are the components of a glacial system that make up the physical mass or motion of the glacier. It is the matter and energy present within the boundaries of the glacial system – ice and snow in the context of glacial systems. It is important to note that these stores are not static, but subject to change. For example, although snow and ice make up the glacier, ablative processes such as sublimation of ice calving remove these from the system. Conversely, more may be added via processes such as precipitation. We often associate stores with that which stays the same or remains stationary, but it is important to remember that the glacial system is dynamic and subject to a lot of change.

What are transfers?

The transfers of a glacial system are the processes that move the components within the stores either to other stores within the system or into or out of the glacial system entirely. Some examples of internal transfers (within a system) may include the movement of ice or snow from one area of the glacier to another or the transfer of gravitational potential energy into kinetic energy. Some inter-glacial transfers may involve precipitation or avalanching (which transfers inputs into the system), or sublimation (which causes matter to output from the system).

What glacial features arise due to the glacial system?

As a result of the combination of these four categories of a glacial system, new abstractions of the glacial system are formed. By abstraction, we mean that the following glacial features can be accounted for in terms of the above four categories, but we discuss them separately using specific terminology due to their importance and complexity. They are:

Glacial mass balance

Glacial mass balance refers to the relationship between the rate of accumulation and ablation of a glacier. It is fundamental to the understanding of glacial movement. Mass balance is described as either positive or negative depending on the rate of mass gain against mass loss:

If mass gain> mass Loss -> positive mass balance.

If mass gain < mass Loss -> negative mass balance.

Inputs and outputs are the primary factors affecting the mass balance of a glacier, and by extension, the cumulative and ablative processes that facilitate these are also key to understanding a glacier’s mass balance.

Glacial movement

Glacial movement is affected by a multitude of factors. We must first understand the nature of thermal, cold-based, and polythermal glaciers, and why we classify glaciers like this. Following this classification we can study the ways in which different types of glaciers move, and why they vary.

Glacial movement is tightly related to glacial mass balance, which in turn is affected by cumulative and ablative processes. These three concepts help us understand glaciation and the significance of its relationship with the global climate. Perhaps glacial movement is particularly important as it is the most illustrative of a changing climate; higher temperatures are correlated with increased glacial retreat while colder temperatures tend to cause significant glacial advances.

Accumulation and ablation

These two processes directly determine mass balance as well as glacial movement, and as such, they should be studied in depth. Cumulative processes refer to those which cause an increase (or accumulation) of mass within a glacial system. Some of these are precipitation, avalanching, and wind transport. Conversely, ablation refers to the processes which remove mass from a glacial system. These include sublimation, calving, and run-off.

What are the main feedback loops within a glacial system?

Positive (movement)

Ice moves, creating friction between the ice and the surface below. This increases the temperature between the two points of contact, and pressure is also increased. This combination increases meltwater, reducing friction between the two surfaces and causing movement.

Negative

As the ice moves at an increased rate due to its melting, the mass of the ice is decreased which leads to a decrease in its gravitational potential energy (GPE). As there is a lower GPE store, less energy is converted to kinetic energy (KE) which causes the ice to slow down and decrease its movement.

Glacial landform system and geography

Glacial movement incurs other processes including erosion, entrainment, transportation, and deposition, forming glacier landforms within its own system.

Erosion

The glacial erosion processes comprise abrasion, plucking/quarrying, crushing, and subaerial freeze-thaw, all of which are processes where the ice or meltwater remove material including rocks and soil. This also results in erosional landscapes.

Abrasion

Abrasion is when the surface of rocks is worn down by the rocks being carried by the glacier. This often results in scratches on the rock surface called striations, and rock flour, which are small particles of rock.

Plucking/quarrying

Plucking/quarrying occurs at the bottom of the sides of the glacier, and it is when parts of rocks freeze to the ice, break off, and is carried by the glacier.

Crushing

Crushing is the process where the pressure of the glacier and the fragments of the rock causes fractures (called chattermarks) on the rock surface.

Subaerial freeze-thaw

This is the process of meltwater entering the cracks of rocks, freezing and expanding, putting pressure on the rock. This repeated process eventually causes the rocks to break.

Entrainment

Entrainment is when the debris is incorporated into the base or the sides of the glacier from supraglacial, subglacial, or endglacier sources.

Supraglacial sources

Supraglacial sources are sediments that have been transported onto the glacier, often fallen from rocky slopes due to freeze-thaw and being washed/blown onto the glacier. It can also include sedimentation from the atmosphere (e.g. volcanic ash).

Subglacial sources

Subglacial sources include sediment from below the glacier such as material frozen from the glacier bed.

Englacial sources

Englacial sources include sediment incorporated within the glacier.

Transportation

Due to glacial entrainment, the sediment and rock move together with the glacial. Subglacial transportation is more common among ice sheets whilst supraglacial and englacial material is more commonly transported by valley glaciers.

Deposition

As the ice melts, the sediment and rocks are dropped either onto the ground or the meltwater. Material can also fall off from the glacier due to the erosion from the surrounding rock surface. The process results in depositional landforms.

Fig. 2 - area of glacial deposition