Question

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Describe the mechanisms that enable glaciers to move and explain why they move. (B)

Short answer

Glaciers move through two main mechanisms: internal deformation and basal sliding. Internal deformation occurs when the weight and pressure of the ice cause the glacier to deform and flow slowly as ice crystals rearrange themselves. Basal sliding occurs when the glacier slides along its base, facilitated by the presence of water acting as a lubricant between the ice and the bedrock. Factors influencing glacier movement include temperature, slope, ice thickness, and the type of bedrock and subglacial materials. Glaciers move primarily due to gravity and their own weight, with the pressure generated by the weight causing the ice to deform and flow, while gravity pulls the glacier downslope.

Step-by-step solution

Glaciers: An Overview

Before we dive into the mechanisms of glacier movement, let us briefly understand what glaciers are. Glaciers are large masses of ice formed by the accumulation and compaction of snow over a long period. They are found in high mountainous regions and polar areas, and they slowly flow and deform over time due to their weight and gravity.

Mechanisms of Glacier Movement

There are two main mechanisms through which glaciers move: internal deformation and basal sliding. 1. Internal Deformation: This process occurs when the weight and pressure of the ice cause the glacier to deform and flow slowly. The ice crystals within the glacier rearrange themselves, resulting in the movement of the ice mass as a whole. 2. Basal Sliding: This process occurs when the glacier slides along its base, specifically over the bedrock or other underlying materials. The movement is facilitated by the presence of water, which acts as a lubricant between the ice and the bedrock. This water can be generated by the melting of the ice due to pressure or geothermal heat.

Factors Influencing Glacier Movement

Several factors can influence the movement of glaciers, including: 1. Temperature: The temperature of the ice affects its deformation rate, with warmer ice deforming more easily than colder ice. In polar regions, where the ice is colder, glacier movement predominantly occurs through basal sliding. 2. Slope: The steeper the slope, the faster the glacier will flow due to the increased gravitational force acting on it. 3. Ice Thickness: Thicker ice has more mass, which leads to increased pressure and deformation, resulting in faster glacier movement. 4. Bedrock and Subglacial Material: The type of bedrock and subglacial materials can influence the basal sliding process. Smooth or soft underlying materials can facilitate sliding, while rough or hard bedrock can impede the glacier's movement.

Why Glaciers Move

Glaciers move primarily due to gravity and their own weight. The pressure generated by the weight of the overlying ice causes the ice to deform and flow, while gravity pulls the glacier downslope. Additionally, the presence of meltwater at the base of the glacier lubricates the contact between the ice and the bedrock, further enhancing the glacier's movement.

Key concepts

Internal Deformation

Glaciers are magnificent but massive ice forms that can move, and one way they do this is through internal deformation. This movement happens primarily due to the immense weight and pressure imposed on the glacier's ice. Think of the glacier as a colossal block of tiny ice crystals. Under the pressure of its own weight, these ice crystals begin to rearrange and slide past one another.

It's kind of like playdough in that it molds and changes shape over time. The rate of internal deformation varies based on several factors such as ice temperature, crystal structure, and the overall pressure applied to the glacier.

• Warmer ice deforms more readily because it's more pliable.
• Higher pressure generally results in more movement.

Through these processes, glaciers can slowly creep across the landscape without needing any extra push from external forces.

Basal Sliding

Basal sliding is another fascinating aspect of glacier movement, and it works quite differently from internal deformation. In basal sliding, the glacier doesn't just move due to changes within itself but also because of what's happening under its belly, so to speak. This process involves the glacier slipping over the bedrock beneath.

Water plays a critical role here, acting as a lubricant to aid the sliding. This water comes from melting ice, sometimes due to pressure or geothermal heat present under the glacier. With the ice slicked by this icy water, the glacier can slide more efficiently over its base.

• Basal sliding occurs more in temperate glaciers, where temperatures hover around the melting point.
• The smoothness or roughness of the underlying bedrock influences how easily glaciers can slide.

This lubrication effect means that movement can be comparatively faster than through internal deformation.

Factors Influencing Glacier Movement

Glacier movement, whether through internal deformation or basal sliding, is affected by several environmental and physical factors, each of which can alter how quickly or slowly a glacier travels. Understanding these factors is crucial.

• Temperature: Warmer glaciers tend to move more due to increased melting and lubrication. Cold glaciers, like those found in polar regions, often rely more on internal deformation.
• Slope: A steeper slope encourages faster glacier movement as gravity pulls more strongly.
• Ice Thickness: Thicker ice holds more weight, driving both pressure and movement.
• Underlying Surface: Smooth surfaces like clay beds can facilitate basal sliding, while rough and jagged rocks can slow things down.

These factors intertwine to determine the movement patterns of glaciers, making each glacier's journey quite unique.

Gravity and Glacier Movement

Gravity plays a vital role in the movement of glaciers. Picture a heavy object sitting on a slope — naturally, it tends to slide downward. This is exactly what happens with glaciers. Their sheer weight and size, combined with gravity, work to pull them downhill.

The glacier's weight exerts pressure, causing the ice to deform under strain, slowly changing shape and moving forward. Meanwhile, gravity ensures this movement is directed downhill. This consistent gravitational force is what makes glaciers flow or slide over various terrains and landscapes.

• Gravity is relentless, constantly encouraging even the smallest movements in glaciers.
• The steeper the glacier's path, the more pronounced the gravitational pull becomes.

Together with other factors like temperature and substrate conditions, gravity ensures that these mighty rivers of ice continue on their paths across the mountains and valleys.