The Anatomy of a Glacier

Summary

This lecture explores the anatomy and dynamics of glaciers, discussing how they form, move, and shape landscapes. Glaciers form through the accumulation of snow, which turns into ice due to pressure and gravity. The balance between the accumulation and ablation zones determines glacier growth or retreat. The lecture also covers glacier movement, erosion, and deposition, explaining processes like abrasion and plucking. Additionally, it delves into the effects of glaciers on the landscape, including the formation of moraines and glacial erratics, and highlights challenges posed by permafrost in cold regions, affecting infrastructure.

Takeaways

• 😀 Glaciers form when snow accumulation exceeds melting, and the snow compresses into ice under its own weight.
• 😀 Glaciers are divided into two zones: the accumulation zone (where ice is added) and the ablation zone (where ice is lost).
• 😀 The equilibrium line separates the accumulation and ablation zones and shifts depending on whether the glacier is advancing or retreating.
• 😀 The glacier's mass balance, determined by the relationship between accumulation and ablation, controls whether a glacier grows or shrinks.
• 😀 Glaciers move slowly due to gravity and pressure, but meltwater at the base can increase movement speed, making it slipperier and facilitating sliding.
• 😀 Glaciers typically move at speeds from almost nothing to a few kilometers per year, with some rare surges reaching much faster speeds.
• 😀 Alpine glaciers erode valleys by abrasion, transforming v-shaped valleys into u-shaped troughs through plucking and scouring.
• 😀 Glacial deposition occurs when glaciers transport and deposit rock and sediment, forming features like moraines, erratics, and glacial drift.
• 😀 Moraines are landforms created by unsorted till deposited by glaciers, with types including lateral moraines (along the sides) and terminal moraines (at the glacier's end).
• 😀 Periglacial landscapes are found in cold regions where permafrost forms. These areas are challenging for infrastructure due to the shifting ground caused by thawing and freezing cycles.

Q & A

What are the two main zones of a glacier?

The two main zones of a glacier are the accumulation zone, where ice and snow accumulate and compact, and the ablation zone, where ice is lost through processes like melting and sublimation.

How do glaciers form?

Glaciers form when there is an accumulation of snow that exceeds melting. The new snow compresses older layers of snow, turning them into ice, and gravity causes the glacier to move.

What determines whether a glacier grows or shrinks?

A glacier's growth or shrinkage depends on its mass balance, which is the balance between the accumulation zone (snow accumulation) and the ablation zone (ice loss). If accumulation exceeds ablation, the glacier grows; if ablation exceeds accumulation, the glacier shrinks.

What is the equilibrium line in a glacier?

The equilibrium line is the dividing line between the accumulation and ablation zones of a glacier. Above the equilibrium line is the accumulation zone, and below it is the ablation zone.

How does a glacier move?

Glaciers move due to the weight and pressure of the ice above. The top of the glacier is rigid and brittle, while the bottom is more flexible, allowing the glacier to bend. Melting at the base creates a slippery layer, which allows the glacier to slide over the land.

What is the typical speed of glacier movement?

The typical speed of glacier movement is slow, ranging from almost nothing to 1-2 kilometers per year on a steep slope. However, certain glaciers, like the Jakobshavn Glacier, can move much faster, up to 7-8 miles per year.

What are the two main processes through which glaciers shape the landscape?

The two main processes are erosion, where glaciers wear down the land as they move, and deposition, where glaciers leave behind sediments they have carried with them.

What is abrasion in the context of glacial erosion?

Abrasion is the process by which a glacier erodes the land by scraping the ground and canyon walls with rocks and sediments it carries. This process deepens and widens valleys.

What are moraines, and how do they form?

Moraines are landforms made of unsorted till (sediment of varying sizes) deposited by glaciers. Lateral moraines form along the sides of glaciers, and terminal moraines form at the glacier's furthest extent.

What is permafrost, and why is it important in periglacial landscapes?

Permafrost is soil or rock that remains frozen for at least two years and is found in cold climates or high elevations. It is crucial in periglacial landscapes because thawing permafrost can cause land shifts, making it challenging for infrastructure development.