Glacier

context: A glacier (US /ˈɡleɪʃər/ or UK /ˈɡlæsiə/) is a persistent body of dense ice that is constantly moving under its own weight; it forms where the accumulation of snow exceeds its ablation (melting and sublimation) over many years, often centuries. Glaciers slowly deform and flow due to stresses induced by their weight, creating crevasses, seracs, and other distinguishing features. They also abrade rock and debris from their substrate to create landforms such as cirques and moraines. Glaciers form only on land and are distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water.
qas: answers: text: many years, often centuries
question: How long does it take glaciers to form?

answers: text: only on land
question: Do glaciers form on land, in the sea, or a combination of both?

answers: text: sea ice and lake ice
question: Which types of ice form on a body of water's surface?

answers: text: stresses induced by their weight
question: What causes glaciers to deform and flow?

answers: text: crevasses, seracs
question: What are some distinguishing glacial features?

context: On Earth, 99% of glacial ice is contained within vast ice sheets in the polar regions, but glaciers may be found in mountain ranges on every continent except Australia, and on a few high-latitude oceanic islands. Between 35°N and 35°S, glaciers occur only in the Himalayas, Andes, Rocky Mountains, a few high mountains in East Africa, Mexico, New Guinea and on Zard Kuh in Iran. Glaciers cover about 10 percent of Earth's land surface. Continental glaciers cover nearly 13,000,000 km2 (5×10^6 sq mi) or about 98 percent of Antarctica's 13,200,000 km2 (5.1×10^6 sq mi), with an average thickness of 2,100 m (7,000 ft). Greenland and Patagonia also have huge expanses of continental glaciers.
qas: answers: text: 99%
question: How much glacial ice is found surrounding the poles?

answers: text: Australia
question: Glaciers are found in mountain ranges on every continent except for which outlier?

answers: text: about 10 percent
question: How much of Earth's land surface do glaciers cover?

answers: text: 2,100 m (7,000 ft)
question: What is the average thickness of an Antartican glacier?

answers: text: 98 percent
question: What percent of Antartica's land is covered by glaciers?

context: Glacial ice is the largest reservoir of freshwater on Earth. Many glaciers from temperate, alpine and seasonal polar climates store water as ice during the colder seasons and release it later in the form of meltwater as warmer summer temperatures cause the glacier to melt, creating a water source that is especially important for plants, animals and human uses when other sources may be scant. Within high altitude and Antarctic environments, the seasonal temperature difference is often not sufficient to release meltwater.
qas: answers: text: glaciers
question: Do Earth's lakes or glaciers hold the most freshwater?

answers: text: warmer summer temperatures
question: What causes glaciers to release meltwater?

answers: text: Antarctic environments
question: In which area are summer temperatures not high enough to release meltwater from glaciers?

answers: text: when other sources may be scant
question: Under what circumstances would humans require water from a glacier?

context: Glacial bodies larger than 50,000 km2 (19,000 sq mi) are called ice sheets or continental glaciers. Several kilometers deep, they obscure the underlying topography. Only nunataks protrude from their surfaces. The only extant ice sheets are the two that cover most of Antarctica and Greenland. They contain vast quantities of fresh water, enough that if both melted, global sea levels would rise by over 70 m (230 ft). Portions of an ice sheet or cap that extend into water are called ice shelves; they tend to be thin with limited slopes and reduced velocities. Narrow, fast-moving sections of an ice sheet are called ice streams. In Antarctica, many ice streams drain into large ice shelves. Some drain directly into the sea, often with an ice tongue, like Mertz Glacier.
qas: answers: text: 50,000 km2 (19,000 sq mi)
question: At what dimensions are glaciers called ice sheets or continental glaciers?

answers: text: two
question: How many extant ice sheets exist?

answers: text: 70 m (230 ft)
question: How much would global sea levels rise if Greenland and Antartica's glaciers were to melt?

answers: text: nunataks
question: What is the term for ice that protrude's from a glacier's surface?

answers: text: ice streams
question: Narrow, fast-moving pathways on an ice sheet are called what?

context: Tidewater glaciers are glaciers that terminate in the sea, including most glaciers flowing from Greenland, Antarctica, Baffin and Ellesmere Islands in Canada, Southeast Alaska, and the Northern and Southern Patagonian Ice Fields. As the ice reaches the sea, pieces break off, or calve, forming icebergs. Most tidewater glaciers calve above sea level, which often results in a tremendous impact as the iceberg strikes the water. Tidewater glaciers undergo centuries-long cycles of advance and retreat that are much less affected by the climate change than those of other glaciers.
qas: answers: text: Tidewater glaciers
question: What are glaciers called that end in the sea?

answers: text: Tidewater glaciers
question: Most glaciers from Greenland, Antarctica, and Southeast Alaska are of which type?

answers: text: much less
question: Are tidewater glaciers more or less affected by climate change than other glaciers?

answers: text: above
question: Do tidewater glaciers calve above or below sea level?

answers: text: As the ice reaches the sea, pieces break off, or calve
question: How are icebergs formed?

context: Thermally, a temperate glacier is at melting point throughout the year, from its surface to its base. The ice of a polar glacier is always below freezing point from the surface to its base, although the surface snowpack may experience seasonal melting. A sub-polar glacier includes both temperate and polar ice, depending on depth beneath the surface and position along the length of the glacier. In a similar way, the thermal regime of a glacier is often described by the temperature at its base alone. A cold-based glacier is below freezing at the ice-ground interface, and is thus frozen to the underlying substrate. A warm-based glacier is above or at freezing at the interface, and is able to slide at this contact. This contrast is thought to a large extent to govern the ability of a glacier to effectively erode its bed, as sliding ice promotes plucking at rock from the surface below. Glaciers which are partly cold-based and partly warm-based are known as polythermal.
qas: answers: text: base alone
question: From where is the temperature of a glacier measured?

answers: text: warm-based glacier
question: Which type of glacier is above or at freezing at it's interface and is able to slide?

answers: text: partly cold-based and partly warm-based
question: What temperature makes a glacier polythermal?

answers: text: always below freezing point from the surface to its base
question: What temperature determines a polar glacier?

answers: text: melting point throughout the year, from its surface to its base
question: What temperature characteristic determines a temperate glacier?

context: Glaciers form where the accumulation of snow and ice exceeds ablation. The area in which a glacier forms is called a cirque (corrie or cwm) - a typically armchair-shaped geological feature (such as a depression between mountains enclosed by arêtes) - which collects and compresses through gravity the snow which falls into it. This snow collects and is compacted by the weight of the snow falling above it forming névé. Further crushing of the individual snowflakes and squeezing the air from the snow turns it into 'glacial ice'. This glacial ice will fill the cirque until it 'overflows' through a geological weakness or vacancy, such as the gap between two mountains. When the mass of snow and ice is sufficiently thick, it begins to move due to a combination of surface slope, gravity and pressure. On steeper slopes, this can occur with as little as 15 m (50 ft) of snow-ice.
qas: answers: text: where the accumulation of snow and ice exceeds ablation
question: Under what circumstances do glaciers form?

answers: text: The area in which a glacier forms
question: What is a cirque?

answers: text: armchair-shaped
question: What shape is a cirque, generally?

answers: text: 15 m (50 ft)
question: How much ice and snow is minimally necessary to begin to slide on steep glaciers?

context: Glaciers are broken into zones based on surface snowpack and melt conditions. The ablation zone is the region where there is a net loss in glacier mass. The equilibrium line separates the ablation zone and the accumulation zone; it is the altitude where the amount of new snow gained by accumulation is equal to the amount of ice lost through ablation. The upper part of a glacier, where accumulation exceeds ablation, is called the accumulation zone. In general, the accumulation zone accounts for 60–70% of the glacier's surface area, more if the glacier calves icebergs. Ice in the accumulation zone is deep enough to exert a downward force that erodes underlying rock. After a glacier melts, it often leaves behind a bowl- or amphitheater-shaped depression that ranges in size from large basins like the Great Lakes to smaller mountain depressions known as cirques.
qas: answers: text: surface snowpack and melt conditions
question: What characteristics determine glacial zones?

answers: text: ablation zone
question: Which glacial zone area reports a net-loss in glacial mass?

answers: text: equilibrium line
question: What is the name of the line seperating the ablation zone from the accumulation zone?

answers: text: 60–70%
question: How much glacial surface area is typically considered accumulation zone?

context: The top 50 m (160 ft) of a glacier are rigid because they are under low pressure. This upper section is known as the fracture zone and moves mostly as a single unit over the plastically flowing lower section. When a glacier moves through irregular terrain, cracks called crevasses develop in the fracture zone. Crevasses form due to differences in glacier velocity. If two rigid sections of a glacier move at different speeds and directions, shear forces cause them to break apart, opening a crevasse. Crevasses are seldom more than 46 m (150 ft) deep but in some cases can be 300 m (1,000 ft) or even deeper. Beneath this point, the plasticity of the ice is too great for cracks to form. Intersecting crevasses can create isolated peaks in the ice, called seracs.
qas: answers: text: they are under low pressure
question: Why are the tops of glaciers rigid?

answers: text: fracture zone
question: Which zone is the top of the glaciers?

answers: text: differences in glacier velocity
question: Why are glacial crevices formed?

answers: text: isolated peaks in the ice
question: What are seracs?

answers: text: 46 m (150 ft)
question: Most crevices are no deeper than what measure?

context: Crevasses can form in several different ways. Transverse crevasses are transverse to flow and form where steeper slopes cause a glacier to accelerate. Longitudinal crevasses form semi-parallel to flow where a glacier expands laterally. Marginal crevasses form from the edge of the glacier, due to the reduction in speed caused by friction of the valley walls. Marginal crevasses are usually largely transverse to flow. Moving glacier ice can sometimes separate from stagnant ice above, forming a bergschrund. Bergschrunds resemble crevasses but are singular features at a glacier's margins.
qas: answers: text: Marginal crevasses
question: Which crevasses form on the edge of the glacier?

answers: text: reduction in speed caused by friction of the valley walls
question: Why do marginal crevasses form on the edge of a glacier?

answers: text: crevasses
question: What do bergschrunds resemble?

answers: text: singular features at a glacier's margins
question: How are bergschrunds different than crevasses?

answers: text: where steeper slopes cause a glacier to accelerate
question: Where do transverse crevasses form?

context: Mean speeds vary greatly, but is typically around 1 m (3 ft) per day. There may be no motion in stagnant areas; for example, in parts of Alaska, trees can establish themselves on surface sediment deposits. In other cases, glaciers can move as fast as 20–30 m (70–100 ft) per day, such as in Greenland's Jakobshavn Isbræ (Greenlandic: Sermeq Kujalleq). Velocity increases with increasing slope, increasing thickness, increasing snowfall, increasing longitudinal confinement, increasing basal temperature, increasing meltwater production and reduced bed hardness.
qas: answers: text: Jakobshavn Isbræ
question: In what area of Greenland can glaciers move 20-30m per day?

answers: text: Velocity
question: Increasing slope, thickness, snowfall, longitudinal confinement, basal temperature, and meltwater production result in increased what?

answers: text: 1 m (3 ft)
question: How far do glaciers generally move per day?

answers: text: trees can establish themselves on surface sediment deposits
question: Why are some glaciers stagnant in Alaska?

context: A few glaciers have periods of very rapid advancement called surges. These glaciers exhibit normal movement until suddenly they accelerate, then return to their previous state. During these surges, the glacier may reach velocities far greater than normal speed. These surges may be caused by failure of the underlying bedrock, the pooling of meltwater at the base of the glacier — perhaps delivered from a supraglacial lake — or the simple accumulation of mass beyond a critical "tipping point". Temporary rates up to 90 m (300 ft) per day have occurred when increased temperature or overlying pressure caused bottom ice to melt and water to accumulate beneath a glacier.
qas: answers: text: periods of very rapid advancement
question: What is a glacial surge?

answers: text: failure of the underlying bedrock
question: What failure causes surges?

answers: text: 90 m (300 ft) per day
question: At what rate have glaciers travelled during surges?

context: In glaciated areas where the glacier moves faster than one km per year, glacial earthquakes occur. These are large scale temblors that have seismic magnitudes as high as 6.1. The number of glacial earthquakes in Greenland peaks every year in July, August and September and is increasing over time. In a study using data from January 1993 through October 2005, more events were detected every year since 2002, and twice as many events were recorded in 2005 as there were in any other year. This increase in the numbers of glacial earthquakes in Greenland may be a response to global warming.
qas: answers: text: one km per year
question: How far does a glacier have to move to cause glacial earthquakes?

answers: text: 6.1
question: How high can the seismic magnitude be of a glacial earthquake?

answers: text: increasing
question: Are Greenland's glacial earthquakes increasing or decreasing as time goes on?

answers: text: July, August and September
question: During which months do glacial earthquakes peak in Greenland?

answers: text: 2005
question: In what year were twice as many glacial earthquakes seen than in any other year in Greenland?

context: Ogives are alternating wave crests and valleys that appear as dark and light bands of ice on glacier surfaces. They are linked to seasonal motion of glaciers; the width of one dark and one light band generally equals the annual movement of the glacier. Ogives are formed when ice from an icefall is severely broken up, increasing ablation surface area during summer. This creates a swale and space for snow accumulation in the winter, which in turn creates a ridge. Sometimes ogives consist only of undulations or color bands and are described as wave ogives or band ogives.
qas: answers: text: alternating wave crests and valleys that appear as dark and light bands of ice on glacier surfaces
question: What are ogives?

answers: text: annual movement of the glacier
question: What does the width of one dark and one light band measure?

answers: text: when ice from an icefall is severely broken up, increasing ablation surface area during summer
question: How are ogives formed?

answers: text: consist only of undulations or color bands
question: Under what conditions are ogives called wave or band ogives?

context: Glaciers are present on every continent and approximately fifty countries, excluding those (Australia, South Africa) that have glaciers only on distant subantarctic island territories. Extensive glaciers are found in Antarctica, Chile, Canada, Alaska, Greenland and Iceland. Mountain glaciers are widespread, especially in the Andes, the Himalayas, the Rocky Mountains, the Caucasus, and the Alps. Mainland Australia currently contains no glaciers, although a small glacier on Mount Kosciuszko was present in the last glacial period. In New Guinea, small, rapidly diminishing, glaciers are located on its highest summit massif of Puncak Jaya. Africa has glaciers on Mount Kilimanjaro in Tanzania, on Mount Kenya and in the Rwenzori Mountains. Oceanic islands with glaciers occur on Iceland, Svalbard, New Zealand, Jan Mayen and the subantarctic islands of Marion, Heard, Grande Terre (Kerguelen) and Bouvet. During glacial periods of the Quaternary, Taiwan, Hawaii on Mauna Kea and Tenerife also had large alpine glaciers, while the Faroe and Crozet Islands were completely glaciated.
qas: answers: text: fifty
question: How many countries contain glaciers?

answers: text: every continent
question: Which continent contains glaciers?

answers: text: Andes, the Himalayas, the Rocky Mountains, the Caucasus, and the Alps
question: Which mountain ranges contain glaciers?

answers: text: Mount Kilimanjaro in Tanzania, on Mount Kenya and in the Rwenzori Mountains
question: Where are glaciers in Africa located?

answers: text: Marion, Heard, Grande Terre (Kerguelen) and Bouvet
question: Which sub-antarctic islands have glaciers?

context: The permanent snow cover necessary for glacier formation is affected by factors such as the degree of slope on the land, amount of snowfall and the winds. Glaciers can be found in all latitudes except from 20° to 27° north and south of the equator where the presence of the descending limb of the Hadley circulation lowers precipitation so much that with high insolation snow lines reach above 6,500 m (21,330 ft). Between 19˚N and 19˚S, however, precipitation is higher and the mountains above 5,000 m (16,400 ft) usually have permanent snow.
qas: answers: text: permanent snow cover
question: Do glaciers require permanent snow or only temporary coverage?

answers: text: 20° to 27° north
question: Between which north latitudes are glaciers not found?

answers: text: 19˚N and 19˚S
question: Between which latitudes to mountains tend to have permanent snow?

answers: text: precipitation is higher
question: Why do mountains between 19N and 19S tend to have snow?

context: Even at high latitudes, glacier formation is not inevitable. Areas of the Arctic, such as Banks Island, and the McMurdo Dry Valleys in Antarctica are considered polar deserts where glaciers cannot form because they receive little snowfall despite the bitter cold. Cold air, unlike warm air, is unable to transport much water vapor. Even during glacial periods of the Quaternary, Manchuria, lowland Siberia, and central and northern Alaska, though extraordinarily cold, had such light snowfall that glaciers could not form.
qas: answers: text: Banks Island, and the McMurdo Dry Valleys
question: Which areas in Antartica are considered polar deserts?

answers: text: they receive little snowfall
question: Why can't glaciers form in polar deserts?

answers: text: warm air
question: Does cold or warm air facilitate the transport of water vapor?

context: Glacial abrasion is commonly characterized by glacial striations. Glaciers produce these when they contain large boulders that carve long scratches in the bedrock. By mapping the direction of the striations, researchers can determine the direction of the glacier's movement. Similar to striations are chatter marks, lines of crescent-shape depressions in the rock underlying a glacier. They are formed by abrasion when boulders in the glacier are repeatedly caught and released as they are dragged along the bedrock.
qas: answers: text: large boulders that carve long scratches in the bedrock
question: What cause glacial stiations?

answers: text: direction of the glacier's movement
question: What can scientists deduct from the direction of the striations?

answers: text: lines of crescent-shape depressions in the rock underlying a glacier
question: What are chatter marks?

answers: text: abrasion when boulders in the glacier are repeatedly caught and released
question: How are chatter marks formed?

context: Glacial moraines are formed by the deposition of material from a glacier and are exposed after the glacier has retreated. They usually appear as linear mounds of till, a non-sorted mixture of rock, gravel and boulders within a matrix of a fine powdery material. Terminal or end moraines are formed at the foot or terminal end of a glacier. Lateral moraines are formed on the sides of the glacier. Medial moraines are formed when two different glaciers merge and the lateral moraines of each coalesce to form a moraine in the middle of the combined glacier. Less apparent are ground moraines, also called glacial drift, which often blankets the surface underneath the glacier downslope from the equilibrium line.
qas: answers: text: after the glacier has retreated
question: When are glacial moraines visible?

answers: text: deposition of material from a glacier
question: How are glacial moraines formed?

answers: text: sides of the glacier
question: Where are lateral moraines found?

answers: text: when two different glaciers merge and the lateral moraines of each coalesce to form a moraine in the middle of the combined glacier
question: How are medial moraines formed?

answers: text: glacial drift
question: What are ground moraines also called?

context: Before glaciation, mountain valleys have a characteristic "V" shape, produced by eroding water. During glaciation, these valleys are widened, deepened, and smoothed, forming a "U"-shaped glacial valley. The erosion that creates glacial valleys eliminates the spurs of earth that extend across mountain valleys, creating triangular cliffs called truncated spurs. Within glacial valleys, depressions created by plucking and abrasion can be filled by lakes, called paternoster lakes. If a glacial valley runs into a large body of water, it forms a fjord.
qas: answers: text: characteristic "V" shape
question: What shape do mountain valleys have pre-glacation?

answers: text: eroding water
question: What gives mountain vallys their characteristic "V" shape before glacation?

answers: text: a glacial valley runs into a large body of water
question: How is a fjord formed?

answers: text: "U"-shaped
question: What shape do glacial valleys have after being widened by glacation?

context: At the start of a classic valley glacier is a bowl-shaped cirque, which has escarped walls on three sides but is open on the side that descends into the valley. Cirques are where ice begins to accumulate in a glacier. Two glacial cirques may form back to back and erode their backwalls until only a narrow ridge, called an arête is left. This structure may result in a mountain pass. If multiple cirques encircle a single mountain, they create pointed pyramidal peaks; particularly steep examples are called horns.
qas: answers: text: the side that descends into the valley
question: On which side is a cirque opened?

answers: text: Cirques
question: Where does ice start accululating in a glacier?

answers: text: arête
question: What is a narrow ridge formed by two cirques eroding back to back called?

answers: text: horns
question: What are extremely steep cirques called?

answers: text: three sides
question: How many sides are closed in a typical cirque?

context: Some rock formations in the path of a glacier are sculpted into small hills called roche moutonnée, or "sheepback" rock. Roche moutonnée are elongated, rounded, and asymmetrical bedrock knobs that can be produced by glacier erosion. They range in length from less than a meter to several hundred meters long. Roche moutonnée have a gentle slope on their up-glacier sides and a steep to vertical face on their down-glacier sides. The glacier abrades the smooth slope on the upstream side as it flows along, but tears loose and carries away rock from the downstream side via plucking.
qas: answers: text: "sheepback" rock
question: What is another name for roche moutonnee?

answers: text: elongated, rounded, and asymmetrical bedrock knobs that can be produced by glacier erosion
question: What are roche moutonnee?

answers: text: less than a meter to several hundred meters long
question: How large are roche moutonnee?

answers: text: gentle slope
question: What shape do roche moutonnee have on their "up" side?

answers: text: steep to vertical face
question: What shape do roche moutonnee have on their "down" side?

context: Large masses, such as ice sheets or glaciers, can depress the crust of the Earth into the mantle. The depression usually totals a third of the ice sheet or glacier's thickness. After the ice sheet or glacier melts, the mantle begins to flow back to its original position, pushing the crust back up. This post-glacial rebound, which proceeds very slowly after the melting of the ice sheet or glacier, is currently occurring in measurable amounts in Scandinavia and the Great Lakes region of North America.
qas: answers: text: Scandinavia and the Great Lakes region of North America.
question: Where is post-glacial rebound occuring most?

answers: text: Large masses, such as ice sheets or glaciers
question: What has the ability to depress the crust of the Earth into the mantle?

answers: text: very slowly
question: With what speed does post-glacial rebound occur?

answers: text: a third of the ice sheet or glacier's thickness
question: How much of a glacier's thickness is usually involved during crust depression into the mantle?