Question

Describe the mechanisms that enable glaciers to move, and explain why they move.

Short answer

A glacier is a large mass of ice that moves due to gravity's influence and environmental factors. Its movement is enabled by two primary mechanisms: internal deformation and basal sliding. Internal deformation occurs when ice within the glacier changes shape due to the weight and pressure exerted on it. Basal sliding occurs when the glacier slides along its base due to the lubrication provided by meltwater. Factors influencing glacier movement include gravity, terrain slope, ice thickness and temperature, and the nature of the underlying bedrock or sediment. Thus, glaciers move due to a combination of gravity, internal deformation, basal sliding, and various environmental conditions.

Step-by-step solution

Define a Glacier

A glacier is a large, slow-moving mass of ice formed by the accumulation, compaction, and recrystallization of snow over many years. Glaciers are crucial components of the Earth's cryosphere and play a significant role in global climate dynamics, sea-level changes, and shaping landscapes.

Explain the Mechanisms behind Glacier Movement

There are two primary mechanisms enabling glacier movement: internal deformation and basal sliding. 1. Internal Deformation - This refers to the process in which the ice within the glacier changes its shape due to the weight and pressure acting on it. The ice crystals slowly rearrange themselves, causing the layers above to move gradually. This movement is driven by the stress exerted on the less dense ice layers at the bottom of the glacier, causing them to deform or creep. 2. Basal Sliding - This mechanism occurs when the glacier slides along its base due to meltwater lubricating the interface between the ice and the underlying bedrock or sediment. The meltwater can be generated by frictional heating between the moving ice and the bedrock below or by geothermal heat from the Earth's interior. Absorbed solar radiation can also cause melting on the glacier's surface, with the resulting water seeping down to its base through crevasses, further facilitating basal sliding. The combination of internal deformation and basal sliding creates the overall movement of a glacier.

Explain Why Glaciers Move

Glaciers move due to the influence of gravity, which constantly acts on the massive weight of the ice. As a result of gravity: 1. Accumulation and compaction of snow increases the glacier's mass, causing it to press down on the underlying layers of ice. With increasing pressure, the ice undergoes internal deformation and moves downslope as the lowest layers of ice deform more readily under the stress. 2. The pressure at the glacier's base also causes some of the ice to melt, generating meltwater, which acts as a lubricant and allows the glacier to slide more easily. In addition to gravity, other factors influencing glacier movement include the slope of the terrain, the thickness and temperature of the ice, and the nature of the bedrock or sediment beneath the glacier. A steeper slope with a thicker, warmer glacier is more likely to facilitate rapid movement, whereas a shallower slope with a thinner, colder glacier will generally experience slower movement. Overall, glaciers move due to a combination of factors, including gravity, internal deformation, basal sliding, slope, and environmental conditions such as temperature, precipitation, and geothermal heat.

Key concepts

Internal Deformation

Internal deformation is one of the key processes through which glaciers move. Imagine a massive weight of ice, pressing down relentlessly under the force of gravity. This pressure causes the ice crystals within the glacier to slowly reposition themselves. It’s almost like the ice is flowing, but much slower and more incrementally.

As the ice deforms, the stress primarily affects the less dense layers at the glacier’s base. These layers tend to creep, slowly shifting the entire glacial mass. This movement is constant but very gradual, often occurring at rates of only a few centimeters to a few meters each year.

• Pressure from the above layers causes internal strain.
• Ice crystals rearrange and realign under stress.
• Result: Slow, persistent flow of ice masses.

Internal deformation is crucial to the glacier’s continuous journey downslope and is akin to squeezing silly putty—it eventually moves even under a continuous, stable pressure.

Basal Sliding

Where internal deformation involves the glacier’s inner structure adjusting, basal sliding is all about what happens underneath the glacier. This mechanism is facilitated mainly by the presence of meltwater at the glacier base, which acts as a lubricant.

Meltwater originates from various sources: it forms due to the frictional heat generated as the glacier grinds over the land, from absorbed solar radiation that melts surface ice, or from geothermal heat from beneath the Earth’s crust. This water, trapped under the glacier, makes the interface between the ice and the ground slippery.

• Meltwater serves as a lubricant.
• Generated by friction, sun, or geothermal heat.
• Facilitates the glacier sliding over bedrock.

This lubrication reduces the friction, allowing the glacier to slide smoothly over its bedrock or sediment base. Basal sliding can lead to faster glacier movement, especially when significant amounts of meltwater are present.

Cryosphere

The cryosphere refers to the frozen water parts of the Earth system, which includes glaciers, ice caps, ice sheets, and permafrost areas. Glaciers are a significant part of the cryosphere, playing an essential role in Earth’s climate and environmental systems.

Understanding the cryosphere helps scientists measure climate change since it directly influences sea levels and global weather patterns. Glaciers within the cryosphere act as reservoirs of freshwater and have a significant impact on the planet’s energy balance due to their high albedo, which reflects sunlight back into space.

• Key component of Earth's climate systems.
• Impacts sea levels and weather patterns.
• Contains vast freshwater reserves.

The cryosphere’s conditions, such as temperature and precipitation, can greatly affect how glaciers move, as these factors influence both internal deformation and basal sliding.

Geophysical Processes

Geophysical processes include the physical activities and phenomena affecting the Earth, such as tectonic shifts, volcanic activities, earthquakes, and, notably, glacier movements. Glacial activity is a type of geophysical process because of how glaciers shape landscapes and affect ecosystems over long timescales.

When glaciers expand or retreat, they modify the land beneath and around them, forming valleys, fjords, and moraines. Their movement is influenced by geophysical factors like gravity, ground heat, and the physical nature of the terrain they pass over, including hills and valleys.

• Earth's physical movements include tectonics & glaciers.
• Glaciers sculpt landscapes.
• Influenced by several geophysical factors.

Understanding these processes helps explain the dynamic nature of glaciers and their effect on shaping today’s world landscapes. This knowledge is crucial for predicting future changes and managing our responses to global geophysical variations.