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Roger Weller, geology instructor

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Glaciers
Zenia Franco
April 26, 2005
Instructor: Mr. Weller

Glaciers

“Glaciers are large masses of ice, resting on land or floating shelf like in the sea adjacent to land”(Sandberg).  Glaciers are made up of many years of snow, ice, rock, sediment, and water.  They are composed of ice, which is one of nature’s most beautiful and elegant substances and can form in the atmosphere as snow (Sandberg). Most glaciers are found at the poles, but glaciers exist on all of the world's continents, even Africa. Australia doesn't have any glaciers; however, it is considered part of Oceania, which includes several Pacific island chains and the large islands of Papua New Guinea and New Zealand. Both of these islands have glaciers.  Each glacier has a different surrounding environment. “Like great rivers of ice, glaciers have sculpted mountains and carved out valleys, and they continue to flow and shape the landscape in many places today” (“All About Glaciers”).

“Glaciers form when yearly snowfall in a region far exceeds the amount of snow and ice that melts in a given summer. In this way, massive quantities of material accumulate in relatively small periods of geologic time” (“What are Glaciers?”). Snowfall is the first step in the formation of glacier ice.  As snow builds up, snowflakes are packed into grains.  The weight of the overlying snow causes the grains below to become coarser.  Melted snow quickly refreezes forming ice. Snow change and how much time it takes to develop into glacier ice depends on the temperature. In an area where there is more snowfall than summer snow melt, perennial snow patches appear in the mountains and remain at the end of summer.  Glaciers can form in areas where summer temperatures are too low for all of the snow to melt. A glacier covered with snow throughout the year is called, Neve. This term refers to the accumulation area at the upper end of a glacier. Glaciologists land their planes in this area, as it is relatively safe from crevassing. 

There are three types of glaciers; ice sheets, ice shelves, and ice caps.  Ice sheets are located in Antarctica and Greenland.  They are large masses of ice, which cover more than 50,000 square kilometers.  Ice Shelves are slabs of glacier ice, which lie flat on the sea (Sandberg). Glaciers that discharge into the sea from higher ground become detached from the bed and float, spreading out to cover large bays. Ice caps are smaller versions of ice sheets.  They cover less than 50,000 square kilometers. Large ice caps can cover an area as large as the entire Seward Peninsula on Alaska’s west coast. Ice accumulates on high areas in the middle of an ice cap and spills down on all sides (Sandberg).

Cirques glaciers, valley glaciers, tidewater glaciers, piedomont glaciers, and ice aprons are all different types of mountain glaciers.  Cirques are bowls or basin carved out of a mountain. They are very short in relation to their width. Valley glaciers are shaped like tongues of ice. They are found in high altitudes. They can flow downwards from cirques, ice caps, highland ice fields, or ice sheets.  Two examples of valley glaciers are Bering and Hubbard Glaciers. They are the longest in America ranging from 200 and 150 kilometers long (Sandberg). Tidewater Glaciers are valley glaciers also, but they enter the sea.  In the water, they either remain grounded or float.  Piedomont glaciers are valley glaciers that spread out into wide lobes (Sandberg).  They are formed where mountain valleys open into larger valleys or onto plains. Ice aprons or hanging glaciers form where mountain slopes seem almost too steep to hold any snow. Ice aprons often make avalanches. There are also warm glaciers and cold glaciers.  Warm glaciers have ice temperatures at melting point.  Melt water is abundant in the summer and continues to flow throughout the winter in warm glaciers.  A well-developed drainage network exists, including moulins, ice lenses and water pockets. They form in most mountain regions outside the Arctic Antarctic. Cold glaciers have ice at temperatures below freezing.  Cold glaciers are frozen to the bed and erode very little.  They are found in the polar-and sub-polar regions (Sandberg).

            Glacier landforms can form by two processes. One form is erosion, a process by which material is worn away by the earth.  Alpine glaciers usually create erosional landforms. The second process by which glacier landforms are formed is by deposition, the laying down of matter by a natural process. The types of glacier landforms that can be created by erosion are fjords, glaciated valleys, arętes, cirques, horns, and tarns. The landforms created by deposition are tills, moraines, kettles, boulders, drumlins, and kames. Both, erosion and deposition can produce distinctive landforms (“What are Glaciers?”).

Glaciers originate on land and move down slope under the influence of its own weight and gravity. Glaciers change and move and they are also known as solid rivers or (“rivers of ice”).  They are known as this because glaciers actually flow. Gravity is the cause of glacier motion.  The ice slowly flows and changes in response to gravity.  A glacier molds itself to the land and also molds the land as it creeps down the valley. Many glaciers slide on their beds, which enable them to move faster.  Rock that falls onto the glacier’s surface is incorporated into the glacier and erodes the bed, forming sediment.  The glacier and its load of rock debris flow down-valley (“All About Glaciers”). A glacier discharges snow from its accumulation area. Sometimes, in places with cold climates with a lot of snow such as Alaska, glaciers flow all the way down to sea level(“All About Glaciers”). These glaciers carve fjords and make icebergs. At the glacier's face, ice which has been melting, fracturing, and has been battered by the sea breaks off as icebergs through a process called calving. Calving is the process, which balances the flow of ice from behind. A glacier does not slide downhill like a block of rock.  The movement occurs internally, below the rigid surface layer, which fractures as the underlying zone moves forward.  Simultaneously, the base creeps and slides along, varying its speed with temperature and the presence of any lubricating water beneath the ice (“All about Glaciers”).

Glaciers can advance or retreat.  Glaciers advance when more snow and ice are added than lost through the processes of calving, melting, or evaporation. They will retreat if less snow and ice are added than are lost. There are three zones to a glacier. The first zone is where snow is added to the glacier and begins to turn to ice. This is known as the accumulation zone (input) (What are Glaciers?”). In this zone the glacier gains snow and ice in the upper region of the glacier.  Water then seeps through accumulated snow and gradually forms horizontal “ice lenses” and vertical “glands.  Eventually, the whole mass compresses into a deep bed of dense ice .The ice flows like a conveyor belt driven by gravity ever mounting snows.  The second zone is the ablation zone (output), where the glacier loses ice through the processes of calving, melting, and evaporation.  In this zone, the glacier loses ice in the lower region of the glacier (“What are Glaciers?”).  Then meltwater flows out to the terminus through hidden channels and tunnels. The oldest ice is the deepest. The third zone is the equilibrium line. The equilibrium line divides the two areas. This spot is like an old-fashioned pair of scales used to weigh gold dust. If the glacier’s scale, or budget is balanced with enough new ice added to replace the loss, the glacier is stable with little advance or retreat. If the balance is tipped, the glacier shifts and either advances or retreats. Glaciers can move by ice flow. Ice flow is when glaciers move by internal deformation and sliding at the base. The ice in the middle of the glacier flows faster than the ice along the sides of the glacier. Glacier bed is another way in which they can move.  Glacier bed is when glaciers move by sliding over bedrock or underlying gravel and rock debris.  With the increased pressure in the glacier, and its weight the individual ice grains slide past one another and the ice moves slowly downhill. The sliding if the glacier over its bed is called the basal slip. Water lubrication is crucial to either process (Sandberg).

            Glacial ice is a different color than regular ice. Glacier ice usually looks blue. It is so blue because the “dense ice of the glacier absorbs every other color of the spectrum except blue--so blue is what we see.  Sometimes glacial ice can appear almost turquoise.  Its crystalline structure strongly scatters blue light”. The ice on a glacier has been there for a really long time and has been compacted downs so that its structure is pretty different than the ice you normally see (Sandberg).

Glaciers also support life.  As glaciers shift and change the face of the earth with their giant hands, they delicately support some of the tiniest creatures alive.  Glaciers create unusual environments sensitive to the animal kingdom’s need for existence.  One life form that a glacier supports is a glacier flea.  They are small black wingless springtail bugs. They live in firn on glaciers.  Another life form is an ice worm.  These worms feed on algae and pollen, as they thrive in the old temperatures of glaciers (“Sandberg”). 

Glaciers require very specific geographical and climatic conditions.  Most are found in regions of high snowfall in winter and cool temperatures in summer.  These conditions assure that the snow accumulating in the winter remains throughout the summer. Typically, such conditions prevail in the polar and high alpine regions.   The amount of precipitation is important to glacial survival. In areas such as Siberia and parts of Antarctica, where low temperatures meet glacier growth requirements, the lack of adequate precipitation, prevent glacial development (“All About Glaciers”).

 “Glaciers are large masses of snow, recrystallized ice and rock debris that accumulate in great quantities and begin to flow outwards and downwards under the pressure of their own weight” (“What are Glaciers?”). Each glacier is different in its own special way. Glaciers are a wonder of nature.  They are massive and incredibly powerful.  Glaciers can carve out the land and change landscapes.  They are powerful moving wonders. They can even be disastrous like the glacier that conquered the Titanic.

 

Picture of the Anatomy of a Glacier:

 

 


Photo and points below from the “All About Glaciers” website

1 The accumulation (input) zone is where a glacier gains snow and ice through snowfall and compression. Ice begins to flow like a conveyor belt, driven by gravity and ever mounting snows.

2 In the lower region, or ablation (output) zone, the glacier loses ice through melting and evaporation. Older ice is carried down to greater and greater depth.

3 An equilibrium line divides the two areas. This spot is like an old fashioned pair of scales used to weigh gold dust. Advancing ice scrapes and grinds the bedrock, boulders, and gravel beneath it and pushes a ridge of terminal moraine in front.

4 Advancing ice scrapes and grinds the bedrock, boulders, and gravel beneath it and pushes a ridge of terminal moraine in front.

5 Another, or tributary, glacier sometimes joins the main flow, adding another strip of lateral moraine debris. The two lateral moraines combine to form a single medial moraine, which now extends down the middle of the glacier towards the snout.

6 When two lateral moraines combine, they form a single medial moraine, which extends down the middle of the glacier towards the snout. When medial moraines come close to one another near the terminus, a glacier may look multicolored or striped.

7 Glacier ice melts and fractures, and the sea often batters it. Finally, chunks of ice break off as icebergs in a process called calving, which balances the flow of ice from behind.

8 Near the terminus (end) of a glacier, its surface thins and stretches and breaks into a mosaic of crevasses.

9 Meltwater flows through hidden channels and tunnels.

10 Snow to Ice: Water seeps through accumulated snow and gradually forms horizontal "ice lenses" and vertical "glands." Eventually, the whole mass compresses into a deep bed of dense ice.

11 Ice Flow: Bending of a vertical bore hole

12 Glacier Bed: Glaciers move by sliding over bedrock or underlying gravel and rock debris. With the increased pressure because of the weight, the individual ice grains slide past one another and the ice moves slowly downhill. Water lubrication is crucial to either process. The sliding of the glacier over its bed is called basal slip.

 

Work Cited

“All About Glaciers”. 15 Mar. 2005.

            http://www.uvm.edu/whale//GlaciersWhatAre.html.

Sandberg, Donna.  “Glacial Power”. 15 Mar. 2005.

            http://www.asf.alaska.edu/2222/intro_begin.html.

“What are Glaciers” 12 Mar. 2005.

            http://inside.org/glaciers/index.html.