glaciers glaciology is the study of glacial activity basic concepts definition of glacier any moving...

GLACIERS

GLACIERS• glaciology is the study of glacial activity

• Basic concepts

• Definition of glacier

• any moving mass of ice on Earth

• Classification of glaciers

• mountain(alpine) glaciers= formed in and restricted to the mountainous areas on Earth and comprise a small amount of total glacial ice on Earth

• continental glaciers=massive ice on continents comprising about 95% of total global ice

GLACIERS Changing of snow to ice

snow fall and accumulates and contains air between flakes

as more snow accumulates, snowflakes farther down are compressed forcing out a lot of the air

with increasing depth and pressure, snow crystallizes to form ice, which can be considered a rock

GLACIERS• Theories and concepts of all glacial ice growth

and demise

• changes in temperature and/or precipitation over a long time are the two most important conditions governing the growth and demise of glacial ice

• continental glaciers

• activity on sun solar flares and sun spots

• some believe a long term change in solar intensity can cause a global temperature change increasing or decreasing glaciers

GLACIERS• greenhouse effect

• Long term increases or decreases of carbon dioxide in our atmosphere can increase or decrease global temperatures to affect amounts of global ice

• increases of CO2: 1) burning of fossil fuels; 2) volcanic activity--emissions of CO2

• decreases of CO2: 1) chemical weathering of extruded igneous rocks

• plant use of CO2 for photosynthesis

GLACIERS• Donn-Ewing concept (not well accepted)

• land bridge across Bering Straits controls amount of precipitation in the region by allowing different temperature bodies of water (Arctic and North Pacific Ocean) to mix when land bridge is submerged ( increased precipitation)and not mix when land bridge is exposed(decreased precipitation)

• this idea may explain the “North American Ice Age”-- glacial ice in Greenland is a remnant of that age

Extent of global ice during North American Ice Age

GLACIERS• atmospheric particulates

• volcanic activity on a large scale can cause large amounts of particulates in the atmosphere resulting in reflection of sun energy and cooler global temperatures

• plate tectonics and position of continents at polar region and variation of Earth’s orbit

• these 2, appear to be more popular

GLACIERSPosition of plates before Continental Drift

GLACIERSChanges of Earth’s Orbital Variations

1. Tilt of Earth’s Axis of Rotation (takes about 40,000 years to cycle from minimum to maximum)

maximum tilt angle can lead to a decrease of glacial activity because warmer summer temperatures melt more south polar ice

minimum tilt angle can lead to an increase of glacial activity because south polar area receives less sunlight

present day tilt, adjusting back from last ice age

GLACIERS2. Shape of Earth’s Orbit (Eccentricity—takes about 100,000 for cycle)

Eccentricity can cause a major climate change

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3. Wobble of Rotation Axis (Precession)

Precession can cause global changes

http://highered.mcgraw-hill.com/sites/0073369365/student_view0/chapter16/milankovitch_cycles.html#

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MILANKOVITCH CYCLES

GLACIERSeach individual variation cannot explain glacial activity, but by combining them as Milankovitch did, appeared to show better results—but still debated by some

What about theories of growth and demise of alpine glaciers ?

growth and demise of alpine glacial ice is more dependent on small term changes as in seasonal temperature and precipitation differences as is present in many global mountainous regions. There can be alpine glaciers active and caused by continental glaciations

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GLACIERS• Alpine and Continental Glacial Regiment

(movement)

• growth and demise of glacial ice is based on rate of accumulation versus the rate of wastage(melting) for alpine and continental glaciers

example of important alpine glacial areas

Photo of snowline and areas of accumulation and wastage for an alpine glacier

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GLACIERS• Alpine and Continental glacial flow at and

below ice surface--brittle zone—crevasses at surface

brittle-crevasse zone slower flow

mobile ice– fastest flow

A lot of friction with rocks—slowest flow

GLACIERS• Glacial deposits and erosion features

• all glacial deposits (Alpine and Continental) are called drift

• till is non-stratified drift and comprised of non sorted or a mixture of different particle sizes (see Wentworth’s scale)--deposited directly by the glacial ice

• outwash is stratified or layered drift with each layer being well sorted--deposited directly by glacial melt water

Photo of till

Example of Non-Layered Till and Layered

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Outwash

Non-sorted Till

Sorted Outwash

GLACIERS• Alpine glacial deposits and erosion features

• deposits--mostly till called moraine • lateral moraine

• formed on sides of and present on surface of glacial ice and results from the plucking and pulverization of rock by the ice

• medial moraine• formed by convergence of 2 lateral

moraines from 2 ice lobes

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• end (terminal) moraine

• a ridge of deposit contouring the shape of front of glacier formed from the discharged of materials moved within the glacier like a conveyor belt

• represents the maximum advance position of the glacier

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lateral moraine formed on sides of glacier

medial moraine formed from 2 lateral moraines from intersecting glaciers

terminal moraine—most forward movement of glacier

GLACIERS• recessional moraine

• a deposit shaped similar to the end moraine formed during a subsequent advancement of glacier during its overall demise

• many recessional moraines may occur during the demise of a glacier

• erosion features

• formed from the plucking nature of the glacier

GLACIERS• cirque

• semi-circular or amphitheater shaped--a tarn or cirque lake can be present ---paternoster lakes are a chain of interconnected tarns

2 cirques and tarns

GLACIERS• horn

• a peaked or pointed feature resulting from the formation of a series of closely associated cirques

• best example is the Matterhorn

Matterhorn in the Alps

GLACIERS• arete

• a jagged or sawtooth ridge left between 2 glacial lobes gouging rock material as they move to a lower elevation

cirques and aretes

GLACIERS• U shaped valley

• is the typical shape of a valley carved by a glacier

• is best observed in the front profile view as you look up the valley

GLACIERS• hanging valley

• formed from a glacial tributary lobe and hangs over the main glacial valley

• best example of this is Bridalveil Falls in Yosemite National Park

Review of some alpine glacial depositional and erosion features

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GLACIERS• Continental glaciers

• glacial ice in Antarctic and Greenland comprise more than 90% of all glacial ice on Earth

• if all the ice melted sea level would rise about 215 feet(195 feet from all ice associated with Antarctic and 20 feet for that from Greenland)

Glacial ice deposits on Antarctic and Greenland

Effects of continental glacial ice formation or melting on sea level

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GLACIERS• erosional features

• there are a few types of erosion features associated with continental glaciers like the Great Lakes and Driftless area in Wisconsin, but the depositional features are more abundant

• depositional features

• till

• ground moraine--an undulating massive blanket like deposit formed on ground where glacial ice was present

GLACIERS• end moraine--see alpine notes

• recessional moraine--see alpine notes

• drumlin--a streamlined symmetric inverted spoon head shaped hill whose steep side faces the direction from which the glacier advanced---Bunker Hill in Boston is a drumlin and is where a famous Revolutionary War battle was fought

Field of drumlins in Baraboo, Wisconsin

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Drumlins—steep side facing direction of glaciers retreat

GLACIERS• Outwash (well sorted)

• outwash plain--a relatively flat massive blanket like deposit consisting of layered and well sorted particles deposited by glacial melt water in the front and sides of the glacial ice

• esker--a winding ridge comprised primarily of sand and gravel layers deposited by a stream flowing in a tunnel beneath a glacier near its terminus

Esker

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GLACIERS• kame--a steep sided hill comprised of

sand and gravel layers originating from the collection of sediment in openings in stagnant ice

• kettle

• hole or lake formed from a large melted block of ice buried in the ground moraine or outwash plain

Review of some continental glacial depositional features

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kettle lakes

esker

drumlinsrecessional moraines

terminal moraine