Glaciers – College Essay Example

The range of possible forms for these glaciers is almost infinite. Small glaciers are typically located in mountainous areas or along coastlines, where they can be found in hollows or shallow indentations. There are two main types of small glaciers: cirque glaciers and alpine glaciers.

Cirque glaciers are confined by valleys and create semicircular basins at the head of the valley as a result of the glacier plucking bedrock while moving downhill. On the other hand, alpine glaciers form on mountain sides and flow downward through valleys.

The text discusses different types of glaciers and their characteristics. These include valley glaciers, ice caps, ice sheets, continental glaciers, and hanging glaciers. It also mentions the formation of piedmont glaciers when two glaciers merge at the base of a mountain. The text further explains how avalanches and icefalls transfer glacial ice from hanging glaciers to larger glaciers below or directly to the valley. Additionally, it mentions that if a valley glacier extends down a valley and covers a gentle slope beyond the mountain range, it is referred to as a piedmont glacier.

Movement

The text highlights that the center of a glacier, where the ice is thickest, moves faster than the edges. It demonstrates this by imagining stones placed in a straight line across a valley glacier's surface, which would eventually become displaced and bent down-valley over time.

A Sliced View

The text describes inserting a bendable pipe into a deep, narrow hole drilled vertically through a glacier from top to bottom for observation.

In a year or two, the pipe would undergo changes in inclination and position, as it is bent into a curve by greater movement at the top of the glacier.

Along with the bending of the pipe, it would also shift down-valley, indicating that the glacier slipped over its bed. This experiment illustrates the two main types of glacial movement: Mysterious Movement. Let's imagine a scenario where a child accidentally breaks their mother's favorite vase while playing baseball indoors and impetuously decides to dispose of the broken pieces in a glacier.

At some point, the person would acknowledge their mistake of not considering the vertical movement of glaciers. If the vase is buried in the accumulation zone, it will eventually appear in the ablation zone. Gradually, their mother would discover the proof. The primary flow direction in the accumulation zone is downward, but it switches to upward in the ablation zone. These shifts in ice movement are linked to two distinct flow regimes within a glacier: Extending Flow, where the glacier becomes elongated and thinner as the flow accelerates.

Compressive Flow A glacier is compressed and thickened where flow is decreasing in velocity.

Bergschrund

A bergschrund is a deep and often wide gap or crevasse, or series of closely spaced crevasses, in ice or firn at or near the head of a valley glacier. A bergschrund separates the moving ice and snow from the relatively immobile ice and snow adhering to the headwall of a valley (or cirque).

Crevasses A crevasse is a deep (some as much as 100 meters deep), nearly vertical fissure, crack, or rift in a glacier.

Crevasses are formed due to stresses resulting from differential movement over the uneven surface beneath a glacier. These crevasses can be hidden by snowbridges and pose a danger when crossing a glacier. Similar to reading tree

ring width, crevasses resemble foliation, which is the banding of ice in the ablation zone. Foliation is comprised of alternating layers of white bubbly ice and bluish ice, with the width of these layers ranging from several millimeters to several meters.

The display of glacier movement is best observed on highly deformed glaciers, particularly at the base of an icefall. Icefalls are found in areas of a glacier that pass over curved bedrock surfaces, creating steep inclines. These sections of the glacier are characterized by numerous crevasses. The main flow of the ice is concentrated in areas beyond the icefalls.

Ice streams, which are currents of ice in an ice sheet or ice cap, flow faster than the surrounding ice. These streams typically flow towards an ocean or ice shelf without any constraints from exposed rock. The surface patterns known as ogives, which are broad bands, curve down-glacier due to the faster movement of ice towards the center of a glacier. Ogives are commonly found below icefalls. A stable glacier refers to a moving body of ice that remains in the same position year after year, with only minor seasonal fluctuations.

In a stable state, a glacier's forward movement is balanced by the recession of the ice edge through melting. The glacier is neither advancing nor retreating, as ablation equals accumulation. For a glacier to be classified as such, it must be moving.

When discussing glaciers, it is important to distinguish between "moving" and "advancing". While glaciers are always in motion by definition, they may not be advancing. Advancement is primarily determined by a glacier's mass balance, rather than its motion. In simple terms, if accumulation of ice exceeds

the amount lost through melting (ablation), the glacier will be advancing.

Glaciers retreat or recede when the amount of snow and ice lost through melting, evaporation, sublimation, wind erosion, and calving is greater than the amount of snow gained through precipitation or wind deposition. This occurs during extended warm periods. Coastal Alaskan glaciers have experienced significant recession due to frontal calving. Icebergs break off progressively from the front of glaciers that end in deep water, leading to a dramatic retreat. The terminus of a glacier can remain stable if it is grounded against a shallow submarine ridge like a moraine shoal. However, once the glacier retreats off the shoal, water fills the space previously occupied by ice.

When a glacier surges, conditions are ideal for calving as it moves or accumulates at its terminus. During a surge, the velocity of the ice can increase dramatically, reaching rates of up to 10 to 100 times the normal velocity. It has even been observed to move at a speed of five meters per hour.

Surging occurs when a specific level of instability is reached and causes rapid downstream movement of ice in the upper ablation zone. The exact mechanism behind surging and the resulting high flow velocity remains unclear. The main factors that greatly influence ablation include precipitation, temperature, and solar radiation. Persistent snowfall is necessary for surges to occur, which is more likely in cooler summers. Additionally, regions at higher latitudes receive less yearly solar radiation and experience longer winters with temperatures below freezing.

Glaciers are found mostly in polar regions, but they can also exist at high altitudes in mid and low latitude areas, especially in alpine regions. The

shape and features of the land surface play a crucial role in glacier formation, including factors like depth of the land and its rough or hollowed surfaces. Moreover, the orientation of the ground surface relative to incoming solar radiation, known as aspect, is an important factor for glacier formation. The slope aspect affects the snowline, with north-facing slopes receiving less direct radiation in the northern hemisphere. However, the coolest slopes are those facing east of north. As new layers of snow accumulate and compress previous layers over time, it gradually transforms into ice through re-crystallization and increased density. After about two winters, this compressed snow reaches an intermediate state called firn before fully becoming glacier ice.

At this point, the density of the ice is approximately half that of water. Over time, larger ice crystals become compressed, reducing the size of air pockets between them. In ancient glacier ice, crystals can reach several inches in length. This process, known as firnification, takes over a hundred years for most glaciers. Snow compresses and becomes denser, transforming into hard ice pellets. The process of firnification causes the formation of dense grainy ice called firn. As firn builds up, it fuses into solid ice. The glacier exerts so much pressure that the firn and snow melt without an increase in temperature, a phenomenon known as compression melting. Unlike other substances, water can melt under pressure. This melting allows the glacier to move and slide around. Glacier speed and movement vary, with most glaciers moving very slowly at a rate of only a few centimeters a day. However, some glaciers can move as fast as 50 meters (160 feet) a

day.

These fast-moving rivers of ice are known as galloping glaciers. Alpine glaciers are formed on mountainsides and move downwards through valleys. Occasionally, alpine glaciers reshape valleys by displacing dirt, soil, and other substances in their path. Alpine glaciers are present in high mountains on all continents except Australia (though there are numerous in New Zealand). Examples of typical alpine glaciers include the Gorner Glacier in Switzerland and the Furtwangler Glacier in Tanzania.

Alpine glaciers, also known as valley glaciers or mountain glaciers, are formed when layers of firn accumulate over time. Once the ice reaches a thickness of about 50 meters (160 feet), the individual firn grains merge together to form a massive solid ice mass. This glacier then starts to move due to compression melting.

The immense weight of the glacier causes the firn and snow to melt, even without an increase in temperature. This phenomenon is unique, as most substances do not melt under pressure (although water is an exception). The resulting meltwater causes the base of the glacier to become smoother, facilitating its spread across the terrain. Guided by gravity, an alpine glacier gradually descends a valley. Hanging glaciers, on the other hand, only cover a portion of a mountain's length.

Avalanches and icefalls move glacial ice from hanging glaciers to a larger glacier below or to the valley directly. Meanwhile, an ice sheet extends from its center. The immense amount of ice in a glacier behaves in a plastic manner, similar to that of a liquid. It flows, oozes, and glides across uneven surfaces, ultimately enveloping everything in its trajectory. Various sections of a glacier advance at varying velocities.

The upper part of

the ice in a glacier moves faster than the base, creating tension and causing cracks called crevasses to form. These crevasses are typically found within the top 50 meters (160 feet) of the glacier and can pose great danger to mountaineers due to their rapid opening and potential for significant depths.

Despite their slow movement, glaciers possess immense power and operate like massive bulldozers, relentlessly advancing each year and obliterating anything in their way - crushing, grinding, and toppling everything in their path. Forests, hills, and mountainsides are no match for the sheer force of glaciers. Occasionally, glaciers even develop on volcanoes, posing an even greater threat when these volcanoes erupt.

Alpine glaciers originate from bowl-shaped mountain hollows known as cirques, causing floods of water, ice, and rocks to flow over the land and into the atmosphere. As the glaciers exceed the capacity of the cirques, they descend downhill and carve out the terrain, resulting in breathtaking and rugged landscapes.

Glaciers erode the land beneath and around them as they move, carrying large amounts of soil, rock, and clay. These glaciers can transport boulders as large as houses, known as glacial erratics, over hundreds or even thousands of kilometers.

Glacial erratics, such as the Big Rock in Okotoks, Alberta, Canada, weigh a staggering 15,000 tons and stand out from their surroundings. These massive quartzite boulders traveled around 1,640 kilometers (500 miles) during the last ice age when they became lodged at the base of glaciers. Acting like rake prongs, these rocks grind against the Earth's surface as they move, leaving behind long striations.

By studying rock striations, geologists can determine the direction of ancient glacier movement. The concept of mass

balance pertains to the disparity between snow and ice accumulation on a glacier and the loss of snow and ice through melting and sublimation. To assess mass balance, scientists calculate the quantity of snow accumulated during winter as well as the remaining amount at the end of the melt season, in addition to measuring how much snow and ice melted during summer. The discrepancy between these two factors determines whether the mass balance is positive or negative. When more snow accumulates in winter than melts in summer, it results in an increase in glacier volume. Conversely, if more snow and ice melt compared to what accumulates, then there is a decrease in glacier volume. Typically, mass balance is expressed in meters of water equivalent, which represents the average thickness gained or lost from the glacier within a specific year.

To indicate the health of a glacier, it is necessary for a typical non-calving glacier to have 60-70% of its area covered in snow at the end of summer. Mass balance, which is the difference between accumulation and ablation, serves as a general indicator. Long-term mass balance records can also indicate local climate changes.

Ablation is measured by placing stakes in the glacier either at the end of the previous melt season or at the beginning of the melt season. On the other hand, accumulation is determined by probing or examining crevasse stratigraphy to measure the thickness of the annual snowpack at multiple locations.

Glacial erosion occurs through three main types: plucking, abrasion, and freeze-thaw processes. Plucking refers to the freezing of meltwater around fragmented and cracked rocks. Abrasion occurs when rocks frozen to the glacier's base scrape against

the bedrock. Freeze-thaw involves the enlargement of cracks in the bedrock (typically found in the back wall) due to the infiltration of meltwater or rain, causing rocks to break away.

Various erosional landforms can result from glacial erosion. Bays are formed when less resistant rock erodes more rapidly than hard rock. Headlands occur when an area of hard rock protrudes into the sea, as these rocks typically alternate between hard and soft layers. Braided streams develop as ice melts and water moves away from the glacial snout into fast-flowing streams while transporting sediment.

Drumlins

Drumlins are large boulders transported by glaciers. By observing their original positions, one can determine the direction of ice flow and trace past ice movements.

Erratics, on the other hand, are also transported by glaciers but are large boulders that do not match the local bedrock. These can similarly be used to study the movement of ice.

Eskers are ridges that are formed as a result of running water underneath the ice. They are a depositional feature of glaciation.

Kames, in contrast, are sediment deposits that are left behind as a glacier slowly melts or remains stationary. These small hills consist of poorly sorted sand and gravel and accumulate in crevasses or indentations on the glacier's surface.

Finally, kettle lakes form when a piece of glacier ice breaks off and becomes buried by glacial till or moraine deposits. As the ice melts over time, it creates a small depression in the land that becomes filled with water.

Kettle lakes are typically small and resemble ponds more than they do lakes. They form when a single block of ice remains in a ground moraine, outwash plain,

or valley floor after a glacier retreats. As this ice block eventually melts, it creates a steep-sided hole that often becomes filled with water. Moraines can be classified into different types: ground (till deposited over a valley floor, found where ice meets rock beneath it), lateral (forms along the edges of glaciers, with material from the valley wall falling onto the ice to create a ridge), medial (formed from the merging of two lateral moraines), push (formed by retreating and then advancing glaciers, indicating a decline in climate after a warm period, identified by rocks pushed upward from their original horizontal positions), recessional (forming at the end of a glacier but across the valley rather than along it, when the retreating ice paused for some time to accumulate material), terminal (forms at the snout of a glacier, indicating the furthest extent of ice across the valley floor, characterized by large amounts of debris and marking the transition from unsorted to sorted material), supraglacial (material on the surface of the glacier, including lateral and medial moraines, loose rock debris, and atmospheric dust settling out), and englacial (any material trapped within the ice).The text describes various features and processes related to glaciers. These include material that falls down crevasses and rocks that are scraped along the valley floor. The Outwash Plain is the largest area of glacial sediment deposited by meltwater streams, situated furthest away from the glacial snout. It is formed from gravel, sand, and clay, with smaller materials carried farthest away. The streams sort the already deposited material, creating the outwash plain, which can be up to 50m thick.

Rock flour is the finely ground remains

of rocks. It is produced when glaciers move across the valley floor, incorporating material from freeze-thaw and debris fallen from valley walls. The meltwater streams remove rock flour from the glacier and often give it a milky blue-white color.

Varves are found in deposits of glacial lakes and consist of two layers of sediment. The lower layer is composed of light-colored sandy material, while the upper layer is made up of dark silt. The number of varves can indicate the age of the lake, with thick varves indicating warm temperatures and increased melting, and thin varves indicating less deposition due to reduced melting and outwash. Analyzing the original debris from varves can provide information about plant types present at the time of deposition.

Cirques are bowl-shaped depressions that form at the heads of mountain glaciers. They are created when glaciers erode backwards into the mountainside, resulting from a combination of frost wedging, glacial plucking, and abrasion.

Sometimes, there are small lakes known as tarns found in the bottom of cirques. Cirques are formed when two cirque glaciers meet and erode the ridge on both sides, resulting in jagged and narrow ridges called aretes. Aretes are knife-edge ridges that occur when the ridges between two adjacent valleys filled with glacial ice are carved out. Horns, such as the famous Matterhorn in Switzerland, are created when a mountain is eroded by several cirque glaciers, leaving behind a steep and pointed peak with ridge-like aretes leading to the top. Horns can be formed when three or more cirques are carved out of a mountain, resulting in a sharp peak called a horn. When glacial ice melts, it gives rise to braided

streams, which are fast flowing streams and rivers that transport large quantities of sediment and debris away from the glacial snout.

If the stream's sediment load is significantly greater than its velocity, it can cause obstructions and alterations to the course of the stream. This results in the stream diverging into multiple segments that continuously split and reconnect. These formations within the stream are known as eyots. Braided streams are typically characterized by their shallow and wide nature, surrounded by unorganized rock debris.

Drumlins are elongated, tear-drop-shaped sedimentary formations that were created subglacially as the ice sheets moved across the landscape during different ice ages. The formation of drumlins is believed to be a result of glaciers either scraping up sediment from the underlying ground surface or eroding/depositing sediment through glacial meltwater, or a combination of these processes. Due to the deposition and shaping of till, sand, and gravel by glacier movement, all drumlins formed by a specific glacier face the same direction, running parallel to the flow of the glacier. In many instances, numerous drumlins are found together, consisting of till (unstratified, unsorted) and exhibiting a streamlined shape aligned with the direction of continental ice movement—a blunt end upstream and a tapered end downstream with a rounded summit.

When a glacier in a smaller tributary valley meets a larger valley, the smaller glacier cannot erode its base down to the floor of the main valley. As a result, when the ice melts, the floor of the tributary valley hangs above the floor of the main valley. This is known as a hanging valley. Waterfalls typically form at the point where the hanging valley intersects with the main

valley. Valleys created by tributary glaciers are called hanging valleys. Glacial valleys are formed when valleys that once contained glacial ice are eroded into a "U" shape in cross section. Conversely, stream erosion creates "V" shaped valleys (see figure 16).

Fjords, which were once occupied by a valley glacier known as a fjord glacier, are narrow inlets along the seacoast. Ice shelves, on the other hand, are sheets of ice floating on water and attached to land. They typically occupy coastal embayments and can extend for hundreds of kilometers from land, reaching thicknesses of 1000 meters. Outwash plains are formed when streams running off a melting glacier become clogged with sediment and create braided streams. These streams deposit poorly sorted stratified sediment in an outwash plain.

These deposits are commonly known as outwash. If the outwash streams erode their deposits, they form river terraces called outwash terraces. Eskers are long, curved ridges of sediment that were deposited by streams that flowed under or within a glacier. Once the ice melts, the sediment left by these streams forms an esker. Paternoster Lake is one of several small, circular stair-stepped lakes formed in separate rock basins along a glaciated valley.

Col is a low point between two peaks that serves as a pass through a mountain range. It is typically formed by two cirques eroding a narrow depression.
Horn refers to a sharp-pointed peak that is pyramid-shaped and is formed when cirques and glaciers surround a mountain summit.
Bergschrund is formed when a wide crack or crevasse opens along the headwall of a glacier and is most visible in summer when the snow cover is gone.
Tarn is a small

mountain lake, usually found in a cirque basin behind rock risers or in an ice-gouged depression.
Paternoster Lake refers to a series of small circular lakes formed in individual rock basins along a glaciated valley.
U-shaped valleys are formed after glaciation, as the continuous freezing and thawing weathers away the rock walls, resulting in a valley with a characteristic U-shape.
Erratics are unique rocks carried by glaciers that differ in size or type from the rocks in their native area.
Truncated spurs occur when glaciers carve through rock, cutting off the edges of interlocking spurs.

Glacial drift is a term for all types of glacial deposits, both sorted and unsorted.
Stratified drift refers to sediment deposits left by glacial meltwater that are sorted by size.The text below provides information about different glacial deposits and periglacial areas.

• Tills: Refers to unstratified and unsorted debris from ice deposits
• Valley Train Deposits: Material that is deposited downvalley of a glacier through melt-water
• Till Plain: Forms behind an end moraine, featuring unstratified coarse till, with low and rolling relief, and a deranged drainage pattern
• Outwash Plains: Refers to glacial stream deposits of stratified drift from melt-water, they are braided and overloaded, and occur beyond a glacial morainal deposit
• Esker: A sinuously curving, narrow deposit of coarse gravel that forms along a melt-water stream channel, developing in a tunnel under a glacier
• Roche Mountonnee: An asymmetrical hill of exposed bedrock; it displays a gently sloping upstream side that has been smoothed and polished by a glacier, and an abrupt, steep downstream side
• Continuous Area: Regions poleward of the -7
  

degree Celsius mean annual temperature isotherm; it affects all surfaces except those under deep lakes or rivers

- Based on temperature rather than the presence of water
- Alpine Permafrost: (Microclimatic factors such as slope orientation and snow cover are important in sustaining these lower latitude regions The Colorado Rockies experience continuous permafrost down to an elevation of 11,150ft and discontinuous permafrost to 5600ft.
- Active Layer: Seasonally frozen ground between the subsurface permafrost and the ground layer.
- Ground Ice: Subsurface water that is frozen in regions of permafrost.– Pore Ice: Subsurface water frozen in the soil’s pore spaces.
- Lenses/Veins: channels extending in any direction
- Segregated Ice: Layer of buried ice that increases in mass by accreting water as the ground freezes
- Intrusive Ice: The freezing of water injected under pressure, as in pingo
- Wedge Ice: Surface water entering a crack and freezing.
- Frost Action The 9% expansion of water as it freezes creates a strong mechanical force.
- Frost Heaving: (vertical movement)– Frost Thrusting: (horizontal movement)
- Cryoturbation: Soil horizons may be disturbed by frost action and appear churned
- Frost Action Landforms Pingo: Large area of frozen ground can develop a heaved up, circular, ice cored mound.
- Palsa: Round or elliptical mound of peat containing a thin perennial ice lense, rather than a core.The text describes various geological phenomena with their corresponding definitions and characteristics. These include:
- Patterned Ground: This refers to

an area where rock accumulations in the form of polygons are developed on the surface due to the presence of ground ice and frost action.
- Solifuction: This is the movement of soil from higher to lower elevation during the thaw cycle.
- Gelifluction: Similar to solifuction, this is the flow of soil from high to lower elevation during the thaw cycle, but specifically in the presence of ground ice or permafrost. It results in the flattening of the landscape, leaving noticeable sag marks.
- Deposits Till: This refers to nonsorted glacial drift that is directly deposited by ice. It consists of a random mixture of angular rocks of different sizes embedded in a matrix of fine-grained, sand-to-clay-sized fragments. This fine-grained material is often referred to as rock flour due to its resemblance to ground-up rock. If till undergoes diagenesis and becomes a rock, it is called a tillite.

Erratics, also known as glacially deposited rocks or fragments, are found on surfaces made of different types of rock. These erratics can be located several kilometers away from their original source. Geologists can use the distribution pattern of erratics to determine the flow directions of the ice that transported them to their current locations. Moraines, on the other hand, are deposits of till that possess a distinct form compared to the bedrock underneath.