Surface Processes

Glaciers and Ice Ages

Glaciers and the Hydrologic Cycle

- reservoir with long residence time

- Glaciers = storage

What is a glacier?

=> thick mass of ice that originates on land

- accumulation, compaction, and re-crystallization of snow.

=> have covered much more of the Earth’s surface in the past

=> agent of erosion, transport, and deposition

What is a glacier?

• Glacial Ice

• Metamorphosed snow

• Sublimation

• Pressure solution

• firn

Types of Glaciers

• 1) Alpine, and 2) Continental

Alpine

- accumulation of glacial ice in the mountains (wet and cold)

- flow down pre-existing stream valleys

- long and narrow

• mechanism for movement or flow = gravity

EX: Alps

Continental

- ice sheets that cover parts or all of continents

- flow out in all directions from one or more growth centers

- obscures topography

- spreads or flows => because of its own weight and gravity

EX: Greenland and Antarctica

Glacial Movement = GRAVITY

=> DEPENDS ON => slope, precipitation, temperature

=> TWO GRAVITY CONTROLLED MECHANISMS

1) Plastic Flow, 2) Sliding

Plastic Flow = movement w/i ice

• ice in lower part of glacier under pressure = plastic and viscous

• ice brittle near surface....so fractures as ice flows over bumps => crevasses

Sliding => ice slips over bedrock at base

- lubricated by liquid water

* all parts of the glacier do not move at the same rate = top moves faster than the base = friction

glaciers = constantly gaining and loosing ice

movement = balance between accumulation and ablation

accum. = ablation = stasis

accum. > ablation = advance

accum. < ablation - retreat

Glacial Erosion

== > two mechanisms

1. Plucking - ice in bedrock fractures

2. Abrasion - scraping = -striations, -polish, -flour

Glacial Erosional Landforms - Alpine

• => V- shaped stream valleys to U- Shaped Valleys