Geology Final: Glaciers

glacier

A large, persistent mass of ice that forms on land by the compaction and recrystallization of snow and moves under its own weight.

difference between a glacier and an iceberg

Glaciers form on land and move; icebergs are floating ice that typically calved off glaciers.

percent of Earth's surface covered by glaciers

About 10%.

alpine glacier

A glacier that forms in mountainous regions, confined to valleys.

continental glacier (ice sheet)

A vast, thick ice mass that covers large areas of a continent; examples: Antarctica and Greenland.

ice cap

A dome-shaped glacier smaller than an ice sheet (<50,000 km²), covering uplands and plateaus.

firn (névé)

A compacted form of snow that's intermediate between snow and glacial ice.

zone of accumulation

The area of a glacier where snowfall adds more mass than is lost.

zone of ablation

The area where ice is lost due to melting, sublimation, or calving.

equilibrium line altitude (ELA)

The line on a glacier where accumulation equals ablation.

glacier's mass balance

Net gain/loss of ice; determines if glacier is advancing (positive), retreating (negative), or stable (balanced).

plastic flow

Internal deformation of ice crystals under pressure, dominant in deep glacier ice.

brittle flow

The fracturing of ice in the upper layer (<~50 m); forms crevasses.

basal slip

When a glacier slides over bedrock, lubricated by meltwater or saturated sediments.

glacial surge

A short-lived, rapid advance of a glacier caused by sudden basal slip or sediment deformation.

glacial plucking

The process by which glaciers loosen and lift blocks of bedrock.

glacial abrasion

The grinding of bedrock by debris embedded in the glacier's base.

landforms created by glacial erosion

U-shaped valleys, cirques, arêtes, horns, hanging valleys, roche moutonnée.

till

Unsorted sediment deposited directly by glacier ice.

moraine

A ridge-like accumulation of till; types include lateral, medial, terminal, and recessional.

drumlin

A streamlined hill made of till, shaped by glacier movement.

kettle lake

A depression left by melting ice blocks, often filled with water.

last major ice age (Quaternary/Pleistocene)

~2.6 million years ago.

Milankovitch cycles

Variations in Earth's orbit (eccentricity, obliquity, precession) that affect climate and glaciation.

length of each Milankovitch cycle

Eccentricity: ~100,000 years; Obliquity: ~41,000 years; Precession: ~23,000 years.

role of greenhouse gases in ice ages

CO₂ and CH₄ amplify orbital effects by trapping heat, influencing glacial advance/retreat.

ice cores reveal

Past climate data (temperature, CO₂ levels, dust) via isotopes and gas bubbles.

δ¹⁸O in ice core studies

A proxy for past temperatures.

sea level during the last glacial maximum

About 120 meters lower than today.

isostatic rebound

The rise of land after removal of glacial weight due to lithospheric depression during glaciation.

roche moutonnée

A rock formation smoothed on one side (stoss) and plucked on the other (lee) by glacier flow.

bergschrund

A crevasse at the upper end of a glacier where moving ice separates from stagnant ice.

rock flour

Fine silt-sized sediment created by glacial grinding.

tarn

A mountain lake formed in a cirque after glacier melt.

What are the main processes involved in glaciation?

Accumulation of snow, compaction into firn and glacial ice, movement of ice due to gravity, erosion (plucking and abrasion), and deposition of glacial sediments.

What is an alpine glacier?

A glacier that forms in mountainous regions and flows down valleys, confined by the surrounding topography.

What is an ice sheet glacier?

A massive, continent-scale glacier that spreads outward in all directions, not confined by topography; examples include those covering Greenland and Antarctica.

What is the zone of accumulation?

The upper part of a glacier where snowfall exceeds melting and sublimation, leading to a net gain of ice.

How does snow become glacial ice?

Snow compacts into firn (dense, granular snow), which recrystallizes into solid glacial ice over time due to pressure.

What is the equilibrium line on a glacier?

The boundary between the zone of accumulation and the zone of ablation; where ice gained = ice lost.

What happens in the zone of ablation?

Ice is lost through melting, sublimation, and calving (ice breaking off into water).

What is the glacial budget?

The balance between accumulation and ablation over a year.

What causes a glacier to advance?

A positive glacial budget: accumulation > ablation.

What causes a glacier to retreat?

A negative glacial budget: ablation > accumulation.

What is plastic flow in glaciers?

Internal deformation of ice crystals under pressure, allowing the glacier to slowly flow like a viscous solid.

What is brittle flow in glaciers?

Fracturing of the upper ~50 meters of glacial ice where it behaves like a rigid solid, forming crevasses.

What is basal slip?

Movement of a glacier over its bed, facilitated by meltwater or saturated sediment at the base.

What is a glacial surge?

A short-lived period of rapid glacier movement due to increased basal lubrication or internal deformation.

How is basal slip involved in glacial surges?

Surges are often caused by sudden increases in basal slip, especially when meltwater accumulates at the base.

What is plucking in glacial erosion?

The process where a glacier freezes onto bedrock and pulls pieces away as it moves.

What is abrasion in glacial erosion?

The grinding of bedrock by rocks embedded in the glacier, creating polished surfaces and striations.

What is a U-shaped valley?

A glacially carved valley with steep sides and a flat floor, formed by the erosion of a V-shaped river valley.

What is a cirque?

A bowl-shaped depression at the head of a glacial valley formed by erosion and freeze-thaw action.

What is a horn?

A sharp, pyramid-shaped peak formed by the erosion of multiple cirques around a mountain summit.

What is a hanging valley?

A smaller glacial valley left 'hanging' above the main valley after a glacier retreats; often creates waterfalls.

What is a roche moutonnée?

A bedrock hill sculpted by glacial abrasion on the stoss side and plucking on the lee side.

What is a moraine?

An accumulation of glacial till deposited along the glacier's margins; includes lateral, medial, terminal, and recessional moraines.

What is till?

Unsorted, unlayered glacial sediment deposited directly by ice.

What causes periodic ice ages on Earth?

Changes in Earth's orbital parameters (Milankovitch cycles) and feedback from greenhouse gas concentrations.

What are Milankovitch cycles?

Natural variations in Earth's orbit and axial tilt, including eccentricity (~100,000 years), obliquity (~41,000 years), and precession (~23,000 years).

How do greenhouse gases influence glacial periods?

Higher CO₂ and CH₄ levels trap heat, contributing to interglacial warming; lower levels promote cooling and glaciation.

How do ice cores help us understand past ice ages?

Ice cores contain trapped air bubbles and isotopic data (e.g., δ¹⁸O) that reveal past temperatures, greenhouse gas levels, and climate conditions.

How often have ice ages occurred recently?

Roughly every 100,000 years over the last 800,000 years, aligned with Milankovitch cycles.

How does sea level change during an ice age?

Sea level drops significantly (~120 meters lower) due to the storage of water in continental ice sheets