Glaciers

Groundwater

Question of the week

What is confined aquifer?

Glaciers

Moving body of ice that forms from the accumulation and compaction of snow

Flows downslope or outward under the influence of gravity and the pressure of their own weight

Cover ~10% of the world’s land surface

High latitude (at the poles): any elevation, even sea level

Mid-latitude: only forms at high elevation

I. Glacier Formation

A. How?

Snow falls and accumulates light and fluffy or heavy and wet

As more snow falls, the weight of overlying snow melts some of the contact points between crystals

Water migrates to low pressure areas and refreezes, binding flakes together

Creates ice

I. Glacier Formation

B. Where?

1. Forms when snow accumulation exceeds snow loss due to summer melting

Accumulation > summer melting

High snow accumulation in winter and then a short or relatively cold summer

2. Above snowline: lowest topographic limit of year-round snow cover

I. Glacier Formation

B. Where?

3. North-facing slopes more likely, in northern hemisphere

South-facing in southern hemisphere - opposite direction of the sun

4. Leeward side of mountain (not the windy side)

I. Glacier Formation

B. Where?

Elevation, precipitation, and aspect

I. Glacier Formation

B. Where?

Above snowline

North-facing slopes

Leeward side

II. Classifying Glaciers

Based on whether the local topography confines then or whether they’re allowed to flow freely

A. Alpine GlaciersB. Continental (ice sheets) glaciers

Valley Glacier

Icecap

Tidewater Glacier

II. Classifying Glaciers

Based on whether the local topography confines then or whether they’re allowed to flow freely

A. Alpine Glaciers

Confined by surrounding bedrock highlands

1. Cirque glaciers: create and occupy semi-circular basins on mountainsides

2. Valley glaciers: flow in preexisting stream valleys

3. Ice caps: form at the tops of mountains, completely bury the underlying landscape

?? Glacier

?? Glacier

Icecap

Tidewater Glacier

Tidewater Glacier

II. Classifying Glaciers

B. (Continental) Ice sheetCompletely unconfined

Much larger scale glacier

Blankets all of the underlying landscape except for the highest

peaks

Flow out in all directions

2 continental ice sheets: Antarctica & Greenland

Greenland average thickness = 5000’, maximum thickness is 10,000’

Antarctic sheet up to 3 miles thick in places!

III. Glacier Flow

A. Mechanisms

1. Internal Deformation (plastic flow)

Ice is brittle until it’s under the pressure of ~165 feet of ice, then it behaves plastically

Crevasses are the large cracks at the surface never >165 ft deep

Planes of atoms within the ice structure will slide past one another

Stress > bond strength between ice crystals

III. Glacier Flow

A. Mechanisms

2. Basal Sliding

Base of glacier is partially melted

Water acts as a lubricant

III. Glacier Flow

B. Rate of Flow

Warmer = faster flow1000” or more a year

Cold = slower flowA few meters a year

Depends on: thickness & gradient as well

High basal fluid pressures = surging glacier (meters/hour)

IV. Anatomy of a glacier

A. Zone of Accumulation

Blanket of snow survives summer melting

Nourished by snowfall

IV. Anatomy of a glacier

B. Zone of Ablation

Snow and ice melt & sublimate in summer

Recognized by bare ice in summerWhere the glacier flows into water:

Calving: ice chunks break off and float away icebergs

IV. Anatomy of a glacier

C. Equilibrium Line = Snow Line

Line that separates the two zones

Can change year to year, climate variations

IV. Anatomy of a glacier

D. Terminus

Toe of a glacier

Snowfall vs Melting & Evaporation (Ablation)

Zone of Accumulation• Snowfall Exceeds Melting & Evaporation • Excess Snow Turns to Ice & Flows Out

Zone of Melting or Ablation • Melting & Evaporation Exceeds Snowfall • Melting Excess Made up by Ice Flowing in

Terminus of Glacier• Snowfall & Inflow = Melting & Evaporation (Ablation)