Glaciers
Glacier - a thick ice mass that originates on land from the accumulation, compaction, and recrystallization of snow. Glacial ice
flows.
Glacier Types
1. Mountain also known as Alpine or Valley Glaciers
• Form at high altitudes
• Smaller than ice sheets
• Lengths greater than widths. Shaped a bit like rivers
• Only cover a small region
2. Continental also known as Ice sheets glacier
• Large scale – cover 10% of Earth’s land
• Form at high latitudes, close to the poles.
Greenland – 1.7 million km2
Antarctica – 13.9 million km2
Glacier movement
1. Internal movement – flowing solid 200 m/yr
• rotation of grains (firn)
• slipping along weak surfaces
• melting and refreezing
2. External movement
• basal slip –slipping on a layer of water between the ice and bedrock 200 m/yr
Glacier budget
In - Zone of accumulation - snow
Out – ablation, general term for loss of ice or snow from a glacier.
1.Melting
2.Calving – chunks breaking off the glacier. If this happens in water the chunks are icebergs.
Glacial Landforms
1. Valley Glaciers – tend to accentuate the landscape (make it sharper)
Hanging valley – a tributary that enters a glacial trough high above the floor of the trough.
Arête – a narrow, knifelike ridge separating two adjacent glaciated valleys.
Horn – a pyramid-like peak formed by glacial action in three or more cirques surrounding a mountain summit.
Tarn – a small lake in a cirque.
Cirque – an amphitheater-shaped basin at the head of a glaciated valley.
Truncated spurs – eroded triangular shaped cliffs in glaciated valleys.
Glacial trough – U-shaped glacial valley
2. Ice Sheets – tend to subdue the landscape (knock down high areas and fill in low areas, flattening the land)
Outwash plain – sand and gravels deposited by glacial melt water.
Kettle lake – a water filled depression left by a glacial ice block.
Esker – ridge of sorted sand and gravel deposited in sub-glacial melt water tunnels.
Drumlin – elongate hills formed when a glacier overrides glacial till
Glacial Deposits- Drift – Sediment deposited on land or in water as a result of glaciation.
Two distinct types
1. Till (unsorted sediments deposited by the ice.)
Moraines - a pile of debris that has been transported and deposited by a glacier.
Drumlin - elongate hills formed when a glacier overrides glacial till.
2. Sorted Sediments (sediments deposited by glacial melt water)
Outwash plain – sand and gravels deposited by glacial melt water.
Esker – ridge of sorted sand and gravel deposited in sub-glacial melt water tunnels.
The Ice Age in Illinois
1.8 million years ago through 10,000 years ago
Three main pulses of ice
1. per-Illinoian (18. Million – 500,000 years ago)
2. Illinoian (300,000 – 125,000 years ago)
3. Wisconsinan (75,000 – 10,000 years ago)
The Milakovitch theory
http://www.indiana.edu/~geol105/images/gaia_chapter_4/milankovitch.htm
The episodic nature of the Earth's glacial and interglacial periods within the present Ice Age (the last couple
of million years) have been caused primarily by cyclical changes in the Earth's circumnavigation of the Sun.
Variations in the Earth's eccentricity, axial tilt, and precession comprise the three dominant cycles,
collectively known as the Milankovitch Cycles for Milutin Milankovitch, the Serbian astronomer and
mathematician who is generally credited with calculating their magnitude. Taken in unison, variations in
these three cycles creates alterations in the seasonality of solar radiation reaching the Earth's surface. These
times of increased or decreased solar radiation directly influence the Earth's climate system, thus impacting
the advance and retreat of Earth's glaciers.
The Atmosphere
Ancient Atmosphere
Consisted Primarily of
 Methane
 Ammonia
 Water vapor
 Hydrogen
This was a reducing environment – no oxygen
Changing Conditions – 3.5 bya
Complex molecules form – amino acids, proteins
Photosynthesis begins – oxygen is produced
Driving forces behind changes
 Ultraviolet radiation
 Lightning
 Radioactive decay
Atmospheric Composition
 Nitrogen 78%
 Oxygen 21%
 Argon 1%
 Carbon Dioxide 0.035%
Water Vapor - Amount of water vapor is highly variable in space and time.
Importance to climate – water vapor transfers heat from warmer to colder regions.
Latent heat – heat released or absorbed when matter changes state.
Layers of the Atmosphere
A. By function
Ozonosphere
Ionosphere
B. By temperature
Troposphere
1. Lowest layer – 0 to 15 km
2. Contains 80% of the mass of the atmosphere.
3. Layer where weather occurs.
4. Temperature decreases with height.
Stratosphere
1. Occurs between 15 and 50 km above the surface.
2. Contains 18% of the mass of the atmosphere.
3. Temperature increases with height.
4. Contains ozone (O3) that shields the surface from ultraviolet (UV) radiation.
Mesosphere
Thermosphere – top layer
Global atmospheric circulation – transfer moisture to higher latitudes
Hadley call 0-30o
Ferrel cell 30o-60o
Polar cell 60o –90o
The Green House Effect – incoming solar radiation consists of short, high energy waves. These waves pass thought the
atmosphere and are absorbed by the Earth. Some of this absorbed energy is then released back into the atmosphere as long, low
energy waves which are absorbed by the particles in the atmosphere and raise the temperature.
Common green house gases are
1. Water vapor
2. Carbon dioxide
3. methane
4. Chlo-floro-carbons (CFCs)
Acid Rain – results from the chemical reaction between water and certain compounds in the atmosphere.
Carbon dioxide
Sulfur oxides (SOx)
Nitrogen oxides (NOx)
The Oceans
Ocean-Atmosphere Links
Exchange of water, carbon dioxide and heat.
Surface currents are driven by atmospheric circulation.
Surface Currents
Transfer heat from one place to another.
Keep the upper 100 meters of the ocean well mixed.
The Ocean is Stratified
Oceans and Climate
Heat transferred from the Equator towards the poles.
Thermohaline Circulation
Driven by difference in temperature and salinity.
Completes cycle in 6 yrs.
Waves
Waves move not water.
Important Parts – Wave length, Crest, Trough.
Waves break when wave base = ½ wave length.
Landforms created by waves
 Barrier Islands
 Sea Arches and Sea Stacks
Tides
Driven by the gravitational influence of the Moon and Sun.
Occur twice daily.
Deserts
Definition
 Less than 250 mm (10 inches) of precipitation.
 Generally lacking in vegetation.
 Cannot support a large population ??
Types of Deserts (5)
Subtropical
 Centered around 30o N and S latitude
 Controlled by air circulation
 Geographically extensive
Continental Interior
 Far from sources of moisture (ocean)
Rainshadow
 Mountain ranges cause barrier to flow of moisture.
Coastal Desert
 Cool dry air blows in from the ocean and evaporates occurs as it warms.
Polar Desert
 Cold air holds very little moisture.
 What little precipitation falls remains as ice for 1000’s of years.
Sediment Transport by Wind
 Surface creep
 Saltation
 Suspension
Sand Dunes Types
 Barchan - Sand supply is limited, steady wind from one direction
 Star - Wind direction varies
 Transverse - Abundant sand, wind from one direction, form perpendicular to wind direction.
 Parabolic – Develop along shorelines from off shore winds
 Linear dunes - limited sand supply, form parallel to the convergence of wind.
The type of dune that develops is dependent on:
•Sand supply
•Wind velocity and variability of wind direction
•Surface over which the dune moves
Deflation – fine sands removed leaving gravel deposits.
Ventifacts – rocks shaped and polished by wind.
Wind transported sediments
Creep – particles too large to be lifted, move by impacts with saltating sediments.
Saltation – bounce along surface
Suspension – small grains are carried by turbulent winds.
Loess – wind-blown silts and clays, derived from nearby deserts or from glacial rock flour.