Types of glaciers based on temperature

Glaciers can be classified by the temperature at their bases, which is the point where the ice meets the valley floor. This classification affects how they move and interact with the ground.

Polar glaciers

Polar glaciers, also known as cold-based glaciers, are typically found in high-latitude regions like the Arctic and Antarctic.

Key features of polar glaciers:

• Their bases remain at temperatures well below the melting point of ice, causing the ice to freeze firmly to the bedrock.
• They experience less surface melting compared to other types.
• These glaciers move very slowly, often at rates of about 0.8 to 1.5 cm per day.

Temperate glaciers

Temperate glaciers, also called warm-based glaciers, occur in lower-latitude areas such as the Himalayas.

Key features of temperate glaciers:

• Their bases are at or above the melting point of ice, leading to the production of meltwater, which is liquid water formed from melting ice.
• This meltwater acts as a lubricant, reducing friction and allowing the glacier to slide more easily downhill.
• Surface ice can melt when temperatures reach 0 °C, with the water seeping down to further lubricate the glacier.
• Friction from movement generates heat, causing more melting and faster flow, often at rates of around 2.5 m per day.

Processes that cause glaciers to move

Glaciers move downhill due to gravity, which creates shear stress — the force pulling the ice downslope. There are three primary processes involved: basal slip, internal deformation, and extensional and compressional flow. These processes often work together, but their dominance depends on the glacier type.

Basal slip

Basal slip occurs when meltwater at the glacier's base allows it to slide over the ground. This is the main movement mechanism for temperate glaciers.

Specific processes within basal slip:

• Rotational slip - This happens when a glacier moves out of a hollow in an arc-like motion. The ice's weight increases pressure on the base, lowering the pressure melting point (PMP), which is the temperature at which ice melts under pressure. This causes easier melting and sliding.
• Regelation creep - Protruding rocks on the valley floor exert pressure on the ice, lowering the PMP and causing melting around them. The meltwater flows past the obstruction and refreezes in areas of lower pressure, speeding up flow upglacier and around the rock while slowing it downglacier.

Internal deformation

Internal deformation involves the ice bending and warping like a viscous liquid without sliding at the base.

How internal deformation works:

• It results from ice crystals shifting and deforming as they move past each other, a process called intergranular flow.
• This is the primary movement method for polar glaciers, as their cold bases do not produce enough meltwater for sliding and rarely reach PMP.

Extensional and compressional flow

These flows involve the glacier fracturing into layers that slip due to varying speeds.

Types of flow:

• Extensional flow - At the glacier's head, where the valley is steep, strong gravity pulls the ice quickly downhill. This creates tension, fracturing the ice into thick layers that slip apart and downward.
• Compressional flow - Lower down, where the valley flattens, slower-moving ice is compressed by faster ice from above. The pressure fractures the ice into layers that slip forward.

Together, these are laminar flows, where individual ice layers move independently.

Factors influencing the rate of glacial movement

The speed of a glacier's movement varies based on several environmental and physical factors. Faster movement generally occurs in temperate glaciers on steep slopes, at the surface, in larger glaciers, over impermeable bedrock, and in narrow valleys.

Slope

Steeper slopes increase the downslope component of the glacier's weight, overcoming friction more easily. Glaciers in steep valleys move faster than those on flat floors due to the stronger gravitational pull.

Temperature

Temperature affects melting and lubrication within the glacier.

Effects of temperature on movement:

• Surface ice melts at 0 °C, but deeper layers have a lower melting point due to pressure.
• Surface ice flows faster than deeper ice, as friction with the bedrock slows movement at the base.
• In polar regions, low temperatures lead to cold-based glaciers that freeze to the bedrock and move slowly without meltwater.

Size

Larger glaciers exert more pressure on their bases. Greater pressure lowers the PMP, increasing basal melting and slip, which results in faster overall movement for bigger glaciers.

Altitude

Altitude influences both temperature and precipitation, creating competing effects.

Effects of altitude on movement:

• Higher altitudes bring more precipitation, leading to greater accumulation (addition of ice) and a positive mass balance, which can speed up movement. However, colder temperatures may cause freezing to the bed, slowing it down.
• Lower altitudes have warmer conditions, promoting basal melting and faster slip, especially in temperate glaciers.
• At sea level, some glacier snouts can surge up to 11 m per day due to instability, known as a glacial surge.

Lithology

Lithology refers to the physical characteristics of rocks beneath the glacier.

Effects of lithology on movement:

• Permeable bedrock absorbs meltwater, reducing lubrication and slowing movement.
• Impermeable bedrock retains meltwater, decreasing friction and increasing speed.
• Softer rocks like clay or chalk allow faster movement by offering less resistance.

Topography

The shape of the valley affects ice thickness and flow.

Effects of topography on movement:

• Narrow valleys thicken the glacier, increasing pressure and speed.
• Wide valleys cause the glacier to spread and thin, reducing pressure and slowing movement.

How mass balance affects glacial movement

Mass balance is the difference between accumulation (gains in ice) and ablation (losses through melting or other processes). It influences movement speed over time.

States of mass balance

• Equilibrium - When accumulation equals ablation, the glacier remains stationary.
• Positive mass balance - More accumulation than ablation leads to growth, increasing downward pressure and speeding up movement.
• Negative mass balance - More ablation than accumulation causes shrinking, reducing pressure and slowing movement.

Changes in mass balance do not affect speed immediately but build up over time.

Positive and negative feedback loops in glacial movement

Feedback loops are cycles where processes within the glacier either amplify or reduce movement speed.

Positive feedback loop

This loop accelerates movement through self-reinforcing processes.

Steps in a positive feedback loop:

1. High meltwater volume enables fast basal slip.
2. Increased friction generates more heat.
3. Additional heat produces more meltwater, further increasing speed.

Negative feedback loop

This loop slows movement by counteracting initial speed increases.

Steps in a negative feedback loop:

1. Fast movement thins the glacier as meltwater increases.
2. Thinning reduces basal pressure and meltwater production.
3. Less meltwater decreases lubrication, slowing the glacier.