GLACIERS

Glaciology is the study of glaciers and glacial activity--this photo shows an alpine glacier area--some glacial deposits have important uses in the cement and concrete industries. Changes in climate can cause glacial formation or demise

I. Basic concepts

A. Definition

a glacier is any moving mass of ice on land
click here to read more on what a glacier is

B. Classification of glaciers

1. Mountain or alpine glaciers

· formed in and restricted to the mountainous areas on Earth and comprise a small amount of the total glacial ice on Earth

2. Continental glaciers or ice sheets

· massive amounts of ice covering continents and comprise about 95% of all glacial ice on Earth

C. Theories and concepts of glacial ice growth and demise

temperature and/or precipitation are the two most important factors governing the growth and death or demise of glacial ice-- this involves long term changes in temperature and/or precipitation

1. Continental glaciers

· a. Activity on sun-- some think a long term change in solar flare intensity or sunspots can affect temperature on the global scale causing increases or decreases of glacial ice on Earth—not well accepted as an explanation for all glaciation

· b. Greenhouse effect---some believe increase (decrease) concentrations of certain gases in our atmosphere such as carbon dioxide (CO₂) and methane can increase (decrease) global temperature causing glacial ice to decrease (increase)---there are both synthetic and natural emissions of both these into the atmosphere- this is still controversial

o some important factors influencing the increase of _CO2 concentration in the atmosphere are: a. burning of fossil fuels; b. volcanic activity (CO₂₎ is second most abundant volatile and most abundant gas emitted by volcanic activity)

o some important factors influencing the decrease of CO₂ concentration in the atmosphere are: a. chemical weathering of rocks--leaching of rocks requires acids as H₂CO₃ which forms from moisture and CO₂ in atmosphere; b. plant use of CO₂ for photosynthesis

· c. Donn-Ewing concept— some think this is not a good explanation for all glaciation

o a land bridge across the Bering Straits controls the amount of precipitation in the region by allowing different temperature bodies of waters (Arctic Ocean and North Pacific Ocean) to mix when the land bridge is submerged and not to mix when the land bridge is exposed--precipitation increases when bodies of water with different temperatures mix resulting in glacial growth, while the amount of precipitation decreases and glaciers die when the water bodies do not mix--the Donn-Ewing concept explains the North American Ice Age and the remnant glacier present in Greenland

o click here to see the extent of glaciers during the Ice Age

· d. Atmospheric particulates – some think by itself is a weak explanation for glaciation

o volcanic activity can emit large concentrations of dust particles which reflect sun energy and if on a large scale can result in cooler global temperatures

· e. Plate tectonics

o the location of Pangaea could have been at the South Pole area causing long term glaciation in certain parts of the world.

o click here to see protocontinent--Pangaea Glaciation or see page 282 in text

· f. Variation in the orbit of Earth--- this appears to be the most popular to explain large glaciations-see page 283 in text for these

o a spherical versus elliptical orbit around the sun (eccentricity) could cause a variation in the temperature on earth---also, a change in the angle of tilt of the Earth's rotation axis with respect to the orbit (obliquity) and the wobbling if the Earth (precession) could also cause a change in temperature.

o Click here to see changes in Earth's orbital variations

o However, each of the three variations of Earth's orbit by themselves, do not explain glaciation. However, if all three are considered, this can explain short termed glaciation. Milankovitch combined these three explaining short termed glaciation on Earth.

o Click here to see the Milankovitch Cycles.

click here to read how often Ice Ages occur

2. 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

D. Glacial regiment

1. Ice accumulation and wastage

· a glacier grows as long as the rate of ice formation in the zone of accumulation is greater than the rate of ice melting (ablation) in the zone of wastage--this is true for both continental and alpine glaciers

· click here to see glacial growth or see pages 266 and 285 in text

· click here to see a photo of zone of accumulation (above snowline) and zone of wastage (below snowline) or see page 267 in text

2. Glacial flow

· glacial ice does not move at the same rate at different levels within the ice--glacial ice is more plastic near its center and brittle at the top--the rate of movement is greatest at the center and top of the glacier and slowest at the bottom where there is friction of ice with rock

· the upper portion of the glacier (brittle zone) has many cracks called crevasses---glaciologists can repel downward in these cracks and study various characteristics of the glacier--see photo on page 278(299)

· click here to see glacial ice movement or see page 266 in text

II. Glacial deposits and erosional features

all glacial deposits are called "glacial drift" and are comprised of two types--1. non-stratified drift called "till" which is non sorted meaning comprised of many different particle sizes (see Wentworth's scale of sedimentary particles)--2. stratified drift called "outwash" which is sorted meaning comprised of essentially the same size particle which results in stratification
outwash is deposited directly from glacial melt water and till directly by the glacial ice
click here to see a photo of till or see page 274 in text

A. Alpine glaciers

1. Deposits

· essentially all alpine glacial deposits consists of till materials called moraines--after the discussion on deposits and erosional features you can see page 275 and these glacial features

o a. lateral moraine--formed on the sides of the glacial ice where bedrock is plucked and pulverized

o b. medial moraine--formed when glacial lobes and lateral moraines merge

o click here to see a photo of lateral and medial moraines

o c. end or terminal moraine--a ridge of deposits contouring the shape of the front of the glacier formed by the "bulldozing" action of the glacier as it grows or advances, and/or in part from accumulation of material which moved along the bottom of the glacier and discharged at the front of the glacier--this deposit represents the point of maximum advance of the glacier

o d. recessional moraine--a deposit shaped similar to the end moraine formed when there are periodic advances by the glacier during the overall retreat or demise of the glacier---there can be many recessional moraines formed during the overall retreat

2. Erosional features

· formed from the plucking nature of the glacier

o a. cirque--is a semi-circular or amphitheater shaped feature--a tarn or cirque lake can form in the cirque and a series of interconnected tarns can form paternoster lakes

o click here to see a photo of cirques and tarns or see page 271 in text

o b. horn--is a peaked or pointed feature resulting from the formation of a series of closely related cirques--best example of this is the Matter Horn in the Alps

o click here to see a photo of the Matterhorn in the Alps or see page 273 in text

o c. arete--is a jagged saw-tooth ridge formed between 2 adjacent glacial lobes moving to lower elevations

o click here to see a photo of aretes or see page 271 in text

o d. U-shaped valley--is the shape of the valley carved by a glacier and best seen in the front profile view

o click here to see a photo of a U-shaped glacial valley see page 272 in text

o e. hanging valley--is a glacial valley formed from a tributary glacial lobe and appears overhanging the main glacial valley--best example of this is Bridalveil Falls in Yosemite National Park

o click here to see a photo of a hanging valley or see page 271 in text

click here to see alpine glacial deposits and erosional features or see page 271 in text

B. Continental glaciers

the glacial ice in Antarctic and Greenland comprise more than 90% of all total glacial ice on Earth and if all the ice were to melt, sea level would rise approximately 215 feet (195 feet from the Antarctic ice and 21 feet from the Greenland ice)
click here to see the Greenland and Antarctic Glaciers or see page 263 in text
click here to see the effects on sea level with global glacial melting or see page 278 in text

1. Erosional features

· there are various erosional features associated with continental glaciers like the Great Lake Basins and the Driftless area in Wisconsin, but the depositional features are much more significant

2. Deposits

· a. Till

o ground moraine--an undulating massive blanket like deposit formed where the ice mass was present

o end or terminal moraine--see the same under topic "alpine deposits" above (II. A. 1. c.)

o recessional moraine-see the same under the topic "alpine deposits above (II. A. 1. d.)

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

o click here to see a photo of a field of drumlins –see page 277 in text for another picture of drumlins

· b. Outwash

o outwash plain--a relatively flat massive blanket like deposit consisting of layered materials deposited by melt water in front and on the sides of the margin of the ice sheet

o 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

o click here to see an aerial photo and location drawing of an esker or see page 277 in text

o kame--a steep sided hill comprised of sand and gravel layers originating when sediment collects in openings in stagnant glacial ice

· kettle hole and kettle lake--formed when a large block of ice becomes lodged in the ground moraine or outwash plain and melts causing the land to collapse

click here to see continental glacial deposits –see page 277 for another picture of continental glacial deposits

click here to read more about topics on glaciers treated above

page 297 click to return