Question

A researcher finds evidence of movement of ice within a glacier. Explain how this movement could occur.

Short answer

Glacier movement occurs through gravitational pull, internal deformation, basal sliding, and the formation of crevasses.

Step-by-step solution

Understand Glacier Structure

Glaciers are large masses of ice that flow over land. They're made up of layers of snow that compact into ice over time. The top layer is brittle and can crack, while the deeper layers are more plastic and can flow.

Gravitational Forces

Due to gravity, glaciers are constantly pulled downhill. This force causes the ice to slowly slide over the bedrock below, contributing to glacier movement.

Internal Deformation

Internal deformation occurs when the weight and pressure from the ice above cause the ice layers within the glacier to stretch and bend, allowing the glacier to flow.

Basal Sliding

Basal sliding happens when meltwater at the bottom of the glacier acts as a lubricant, reducing friction and enabling the ice to slide over the base rock. This can increase movement speed.

Ice Fracturing and Crevasses

In the upper layers, where ice is more brittle, tension can cause cracks, known as crevasses, to form. These fractures allow for small amounts of ice movement as the glacier flows.

Key concepts

Internal Deformation

Inside a glacier, the immense weight of accumulated ice exerts significant pressure on the layers below. This pressure causes the deeper sections, often described as more "plastic," to deform and change shape. This process, known as internal deformation, plays a crucial part in how glaciers move. The deeper ice layers can stretch, bend, and flow under this pressure, much like a slow-moving river within the glacier itself.
This flow is influenced by:

• The temperature, as warmer ice deforms more easily.
• The thickness of the ice above, as heavier ice exerts more pressure.
• The slope of the glacier, since steeper slopes encourage faster flow.

Internal deformation is a key mechanism in glacier dynamics, allowing for gradual movement even in the absence of surface water or basal sliding.

Basal Sliding

Basal sliding is another important mechanism that contributes to glacier movement. It involves the sliding of glacier ice over the bedrock surface beneath it. This process is often aided by meltwater that acts as a lubricant, reducing the friction between the ice and the rock.
The presence of water impacts basal sliding by:

• Forming a slippery surface that reduces resistance from the bedrock.
• Increasing pressure at the base when water accumulates, lifting the ice slightly.
• Acting according to temperature variations, as warmer temperatures may increase melting.

Basal sliding can lead to significant changes in a glacier's speed of movement, often making it faster during warmer months when meltwater production is higher.

Crevasses

The top layer of ice on a glacier is prone to fractures due to its brittle nature. These fractures, called crevasses, form where the ice is stretched beyond its breaking point. They are most commonly found on the surface where tension occurs due to the glacier's movement over uneven terrain.
Crevasses are influenced by several factors:

• Tension caused by differential movement of sections of the glacier.
• Changes in the gradient of the glacier bed.
• Alterations in the glacier's speed or direction.

Understanding crevasses is important for safety in glacier areas, and they also offer insight into the stresses affecting glacier dynamics.

Glacier Movement Mechanics

The movement of glaciers is influenced by both internal and external forces, leading to complex dynamics. The mechanics of glacier movement can be categorized into internal deformation of the ice and movement along the glacier bed.

• Internal Processes: Include the plastic flow of deep ice and the adjustments to stress and gravitational pull.
• External Processes: Such as basal sliding, which involves external factors like temperature and water presence.

These processes together allow glaciers to transport vast amounts of ice and sediment across the landscape, reshaping environments over time. Comprehending glacier movement mechanics is vital for predicting changes in glacial areas and understanding the broader impacts on regional ecosystems and global sea levels.