Glacier

Last updated

The Baltoro Glacier in northern Pakistan. At 62 kilometres (39 mi) in length, it is one of the longest alpine glaciers on earth. Baltoro glacier from air.jpg
The Baltoro Glacier in northern Pakistan. At 62 kilometres (39 mi) in length, it is one of the longest alpine glaciers on earth.
Aerial view of a glacier in Chugach State Park, Alaska, United States. Parque estatal Chugach, Alaska, Estados Unidos, 2017-08-22, DD 92.jpg
Aerial view of a glacier in Chugach State Park, Alaska, United States.
Ice calving from the terminus of the Perito Moreno Glacier in western Patagonia, Argentina Perito Moreno Glacier Patagonia Argentina Luca Galuzzi 2005.JPG
Ice calving from the terminus of the Perito Moreno Glacier in western Patagonia, Argentina
The Aletsch Glacier, the largest glacier of the Alps, in Switzerland Grosser Aletschgletscher 3178.JPG
The Aletsch Glacier, the largest glacier of the Alps, in Switzerland
The Quelccaya Ice Cap is the second largest glaciated area in the tropics, in Peru Quelccaya Glacier.jpg
The Quelccaya Ice Cap is the second largest glaciated area in the tropics, in Peru

A glacier ( US: /ˈɡlʃər/ or UK: /ˈɡlæsiər, ˈɡlsiər/ ) 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.

American English Set of dialects of the English language spoken in the United States

American English, sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. American English is considered one of the most influential dialects of English globally, including on other varieties of English.

British English is the standard dialect of English language as spoken and written in the United Kingdom. Variations exist in formal, written English in the United Kingdom. For example, the adjective wee is almost exclusively used in parts of Scotland and Ireland, and occasionally Yorkshire, whereas little is predominant elsewhere. Nevertheless, there is a meaningful degree of uniformity in written English within the United Kingdom, and this could be described by the term British English. The forms of spoken English, however, vary considerably more than in most other areas of the world where English is spoken, so a uniform concept of British English is more difficult to apply to the spoken language. According to Tom McArthur in the Oxford Guide to World English, British English shares "all the ambiguities and tensions in the word 'British' and as a result can be used and interpreted in two ways, more broadly or more narrowly, within a range of blurring and ambiguity".

Ice water frozen into the solid state

Ice is water frozen into a solid state. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color.

Contents

On Earth, 99% of glacial ice is contained within vast ice sheets (also known as "continental glaciers") in the polar regions, but glaciers may be found in mountain ranges on every continent including Oceania's high-latitude oceanic island countries such as New Zealand and Papua New Guinea. 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. [1] Glaciers cover about 10 percent of Earth's land surface. Continental glaciers cover nearly 13 million km2 (5 million sq mi) or about 98 percent of Antarctica's 13.2 million km2 (5.1 million sq mi), with an average thickness of 2,100 m (7,000 ft). Greenland and Patagonia also have huge expanses of continental glaciers. [2]

Earth Third planet from the Sun in the Solar System

Earth is the third planet from the Sun, and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth orbits around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.

Ice sheet large mass of glacier ice

An ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than 50,000 km2 (19,000 sq mi). The only current ice sheets are in Antarctica and Greenland; during the last glacial period at Last Glacial Maximum (LGM) the Laurentide ice sheet covered much of North America, the Weichselian ice sheet covered northern Europe and the Patagonian Ice Sheet covered southern South America.

Mountain range A geographic area containing several geologically related mountains

A mountain range or hill range is a series of mountains or hills ranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have arisen from the same cause, usually an orogeny. Mountain ranges are formed by a variety of geological processes, but most of the significant ones on Earth are the result of plate tectonics. Mountain ranges are also found on many planetary mass objects in the Solar System and are likely a feature of most terrestrial planets.

Glacial ice is the largest reservoir of fresh water on Earth. [3] 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.

Fresh water naturally occurring water with low concentrations of dissolved salts

Fresh water is any naturally occurring water except seawater and brackish water. Fresh water includes water in ice sheets, ice caps, glaciers, icebergs, bogs, ponds, lakes, rivers, streams, and even underground water called groundwater. Fresh water is generally characterized by having low concentrations of dissolved salts and other total dissolved solids. Though the term specifically excludes seawater and brackish water, it does include mineral-rich waters such as chalybeate springs.

Meltwater

Meltwater is water released by the melting of snow or ice, including glacial ice, tabular icebergs and ice shelves over oceans. Meltwater is often found in the ablation zone of glaciers, where the rate of snow cover is reducing. Meltwater can be produced during volcanic eruptions, in a similar way in which the more dangerous lahars form.

Water resources sources of water that are potentially useful

Water resources are natural resources of water that are potentially useful. Uses of water include agricultural, industrial, household, recreational and environmental activities. All living things require water to grow and reproduce.

Since glacial mass is affected by long-term climatic changes, e.g., precipitation, mean temperature, and cloud cover, glacial mass changes are considered among the most sensitive indicators of climate change and are a major source of variations in sea level.

Climate Statistics of weather conditions in a given region over long periods

Climate is defined as the average state of everyday's weather condition over a period of 30 years. It is measured by assessing the patterns of variation in temperature, humidity, atmospheric pressure, wind, precipitation, atmospheric particle count and other meteorological variables in a given region over long periods of time. Climate differs from weather, in that weather only describes the short-term conditions of these variables in a given region.

Temperature physical property of matter that quantitatively expresses the common notions of hot and cold

Temperature is a physical quantity expressing hot and cold. It is measured with a thermometer calibrated in one or more temperature scales. The most commonly used scales are the Celsius scale, Fahrenheit scale, and Kelvin scale. The kelvin is the unit of temperature in the International System of Units (SI), in which temperature is one of the seven fundamental base quantities. The Kelvin scale is widely used in science and technology.

Cloud cover fraction of the sky obscured by clouds when observed from a particular location

Cloud cover refers to the fraction of the sky obscured by clouds when observed from a particular location. Okta is the usual unit of measurement of the cloud cover. The cloud cover is correlated to the sunshine duration as the least cloudy locales are the sunniest ones while the cloudiest areas are the least sunny places.

A large piece of compressed ice, or a glacier, appears blue, as large quantities of water appear blue. This is because water molecules absorb other colors more efficiently than blue. The other reason for the blue color of glaciers is the lack of air bubbles. Air bubbles, which give a white color to ice, are squeezed out by pressure increasing the density of the created ice.

Blue ice (glacial)

Blue ice occurs when snow falls on a glacier, is compressed, and becomes part of the glacier. Air bubbles are squeezed out and ice crystals enlarge, making the ice appear blue.

Color of water Water color in different conditions

The color of water varies with the ambient conditions in which that water is present. While relatively small quantities of water appear to be colorless, pure water has a slight blue color that becomes a deeper blue as the thickness of the observed sample increases. The blue hue of water is an intrinsic property and is caused by selective absorption and scattering of white light. Dissolved elements or suspended impurities may give water a different color.

The word glacier is a loanword from French and goes back, via Franco-Provençal, to the Vulgar Latin glaciārium, derived from the Late Latin glacia, and ultimately Latin glaciēs, meaning "ice". [4] The processes and features caused by or related to glaciers are referred to as glacial. The process of glacier establishment, growth and flow is called glaciation. The corresponding area of study is called glaciology. Glaciers are important components of the global cryosphere.

A loanword is a word adopted from one language and incorporated into another language without translation. This is in contrast to cognates, which are words in two or more languages that are similar because they share an etymological origin, and calques, which involve translation.

French language Romance language

French is a Romance language of the Indo-European family. It descended from the Vulgar Latin of the Roman Empire, as did all Romance languages. French evolved from Gallo-Romance, the spoken Latin in Gaul, and more specifically in Northern Gaul. Its closest relatives are the other langues d'oïl—languages historically spoken in northern France and in southern Belgium, which French (Francien) has largely supplanted. French was also influenced by native Celtic languages of Northern Roman Gaul like Gallia Belgica and by the (Germanic) Frankish language of the post-Roman Frankish invaders. Today, owing to France's past overseas expansion, there are numerous French-based creole languages, most notably Haitian Creole. A French-speaking person or nation may be referred to as Francophone in both English and French.

Franco-Provençal language Gallo-Romance language spoken in France, Italy and Switzerland

Franco-Provençal is a dialect group within Gallo-Romance spoken in east-central France, western Switzerland, northwestern Italy, and in enclaves in the Province of Foggia in Apulia, Italy.

Types

Classification by size, shape and behavior

Mouth of the Schlatenkees Glacier near Innergschloss, Austria Glacier mouth.jpg
Mouth of the Schlatenkees Glacier near Innergschlöß, Austria

Glaciers are categorized by their morphology, thermal characteristics, and behavior. Alpine glaciers form on the crests and slopes of mountains. A glacier that fills a valley is called a valley glacier, or alternatively an alpine glacier or mountain glacier. [5] A large body of glacial ice astride a mountain, mountain range, or volcano is termed an ice cap or ice field . [6] Ice caps have an area less than 50,000 km2 (19,000 sq mi) by definition.

Glacial bodies larger than 50,000 km2 (19,000 sq mi) are called ice sheets or continental glaciers. [7] 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. [8] They contain vast quantities of fresh water, enough that if both melted, global sea levels would rise by over 70 m (230 ft). [9] 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. [10] Narrow, fast-moving sections of an ice sheet are called ice streams . [11] [12] In Antarctica, many ice streams drain into large ice shelves. Some drain directly into the sea, often with an ice tongue, like Mertz Glacier.

The Grotta del Gelo is a cave of Etna volcano, the southernmost glacier in Europe GrottaGelo.jpg
The Grotta del Gelo is a cave of Etna volcano, the southernmost glacier in Europe
Sightseeing boat in front of a tidewater glacier, Kenai Fjords National Park, Alaska Fjordsglacier.jpg
Sightseeing boat in front of a tidewater glacier, Kenai Fjords National Park, Alaska

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. [13]

Classification by thermal state

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 the freezing point from the surface to its base, although the surface snowpack may experience seasonal melting. A subpolar 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 its basal temperature. 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. [14] 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. [15] Glaciers which are partly cold-based and partly warm-based are known as polythermal. [14]

Formation

Gorner Glacier in Switzerland GornerGlacier 002.jpg
Gorner Glacier in Switzerland

Glaciers form where the accumulation of snow and ice exceeds ablation. A glacier usually originates from a landform called 'cirque' (or 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 that 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.

A packrafter passes a wall of freshly exposed blue ice on Spencer Glacier, in Alaska. Glacial ice acts like a filter on light, and the more time light can spend traveling through ice, the bluer it becomes. Packrafting at Spencer Glacier. Chugach National Forest, Alaska.jpg
A packrafter passes a wall of freshly exposed blue ice on Spencer Glacier, in Alaska. Glacial ice acts like a filter on light, and the more time light can spend traveling through ice, the bluer it becomes.

In temperate glaciers, snow repeatedly freezes and thaws, changing into granular ice called firn. Under the pressure of the layers of ice and snow above it, this granular ice fuses into denser and denser firn. Over a period of years, layers of firn undergo further compaction and become glacial ice. Glacier ice is slightly less dense than ice formed from frozen water because it contains tiny trapped air bubbles.

Glacial ice has a distinctive blue tint because it absorbs some red light due to an overtone of the infrared OH stretching mode of the water molecule. Liquid water is blue for the same reason. The blue of glacier ice is sometimes misattributed to Rayleigh scattering due to bubbles in the ice. [16]

A glacier cave located on the Perito Moreno Glacier in Argentina 153 - Glacier Perito Moreno - Grotte glaciaire - Janvier 2010.jpg
A glacier cave located on the Perito Moreno Glacier in Argentina

Structure

A glacier originates at a location called its glacier head and terminates at its glacier foot, snout, or terminus.

Glaciers are broken into zones based on surface snowpack and melt conditions. [17] 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.

The accumulation zone can be subdivided based on its melt conditions.

  1. The dry snow zone is a region where no melt occurs, even in the summer, and the snowpack remains dry.
  2. The percolation zone is an area with some surface melt, causing meltwater to percolate into the snowpack. This zone is often marked by refrozen ice lenses, glands, and layers. The snowpack also never reaches melting point.
  3. Near the equilibrium line on some glaciers, a superimposed ice zone develops. This zone is where meltwater refreezes as a cold layer in the glacier, forming a continuous mass of ice.
  4. The wet snow zone is the region where all of the snow deposited since the end of the previous summer has been raised to 0 °C.

The health of a glacier is usually assessed by determining the glacier mass balance or observing terminus behavior. Healthy glaciers have large accumulation zones, more than 60% of their area snowcovered at the end of the melt season, and a terminus with vigorous flow.

Following the Little Ice Age's end around 1850, glaciers around the Earth have retreated substantially. A slight cooling led to the advance of many alpine glaciers between 1950 and 1985, but since 1985 glacier retreat and mass loss has become larger and increasingly ubiquitous. [18] [19] [20]

Motion

Shear or herring-bone crevasses on Emmons Glacier (Mount Rainier); such crevasses often form near the edge of a glacier where interactions with underlying or marginal rock impede flow. In this case, the impediment appears to be some distance from the near margin of the glacier. Chevron Crevasses 00.JPG
Shear or herring-bone crevasses on Emmons Glacier (Mount Rainier); such crevasses often form near the edge of a glacier where interactions with underlying or marginal rock impede flow. In this case, the impediment appears to be some distance from the near margin of the glacier.

Glaciers move, or flow, downhill due to gravity and the internal deformation of ice. [21] Ice behaves like a brittle solid until its thickness exceeds about 50 m (160 ft). The pressure on ice deeper than 50 m causes plastic flow. At the molecular level, ice consists of stacked layers of molecules with relatively weak bonds between layers. When the stress on the layer above exceeds the inter-layer binding strength, it moves faster than the layer below. [22]

Glaciers also move through basal sliding. In this process, a glacier slides over the terrain on which it sits, lubricated by the presence of liquid water. The water is created from ice that melts under high pressure from frictional heating. Basal sliding is dominant in temperate, or warm-based glaciers.

Although evidence in favour of glacial flow was known by the early 19th century, other theories of glacial motion were advanced, such as the idea that melt water, refreezing inside glaciers, caused the glacier to dilate and extend its length. As it became clear that glaciers behaved to some degree as if the ice were a viscous fluid, it was argued that "regelation", or the melting and refreezing of ice at a temperature lowered by the pressure on the ice inside the glacier, was what allowed the ice to deform and flow. James Forbes came up with the essentially correct explanation in the 1840s, although it was several decades before it was fully accepted. [23]

Perito Moreno glacier Pexels-photo-25416.jpg
Perito Moreno glacier

Fracture zone and cracks

Ice cracks in the Titlis Glacier TitlisIceCracks.jpg
Ice cracks in the Titlis Glacier

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.

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.

Crevasses make travel over glaciers hazardous, especially when they are hidden by fragile snow bridges.

Crossing a crevasse on the Easton Glacier, Mount Baker, in the North Cascades, United States Glaciereaston.jpg
Crossing a crevasse on the Easton Glacier, Mount Baker, in the North Cascades, United States

Below the equilibrium line, glacial meltwater is concentrated in stream channels. Meltwater can pool in proglacial lakes on top of a glacier or descend into the depths of a glacier via moulins. Streams within or beneath a glacier flow in englacial or sub-glacial tunnels. These tunnels sometimes reemerge at the glacier's surface. [24]

Speed

The speed of glacial displacement is partly determined by friction. Friction makes the ice at the bottom of the glacier move more slowly than ice at the top. In alpine glaciers, friction is also generated at the valley's side walls, which slows the edges relative to the center.

Mean speeds vary greatly, but is typically around 1 m (3 ft) per day. [25] 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.

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. [26] These surges may be caused by failure of the underlying bedrock, the pooling of meltwater at the base of the glacier [27]  — perhaps delivered from a supraglacial lake  — or the simple accumulation of mass beyond a critical "tipping point". [28] 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.

In glaciated areas where the glacier moves faster than one km per year, glacial earthquakes occur. These are large scale earthquakes that have seismic magnitudes as high as 6.1. [29] [30] The number of glacial earthquakes in Greenland peaks every year in July, August and September and increased rapidly in the 1990s and 2000s. 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. [30]

Ogives

Ogives (or Forbes bands) [31] 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. [32] Sometimes ogives consist only of undulations or color bands and are described as wave ogives or band ogives. [33]

Geography

Black ice glacier near Aconcagua, Argentina Black-Glacier.jpg
Black ice glacier near Aconcagua, Argentina

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, Argentina, Chile, Canada, Alaska, Greenland and Iceland. Mountain glaciers are widespread, especially in the Andes, the Himalayas, the Rocky Mountains, the Caucasus, Scandinavian mountains, and the Alps. Snezhnika glacier in Pirin Mountain, Bulgaria with a latitude of 41°46′09″ N is the southernmost glacial mass in Europe. [34] Mainland Australia currently contains no glaciers, although a small glacier on Mount Kosciuszko was present in the last glacial period. [35] In New Guinea, small, rapidly diminishing, glaciers are located on its highest summit massif of Puncak Jaya. [36] Africa has glaciers on Mount Kilimanjaro in Tanzania, on Mount Kenya and in the Rwenzori Mountains. Oceanic islands with glaciers include Iceland, several of the islands off the coast of Norway including Svalbard and Jan Mayen to the far North, New Zealand and the subantarctic islands of Marion, Heard, Grande Terre (Kerguelen) and Bouvet. During glacial periods of the Quaternary, Taiwan, Hawaii on Mauna Kea [37] and Tenerife also had large alpine glaciers, while the Faroe and Crozet Islands [38] were completely glaciated.

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.

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, [39] and central and northern Alaska, [40] though extraordinarily cold, had such light snowfall that glaciers could not form. [41] [42]

In addition to the dry, unglaciated polar regions, some mountains and volcanoes in Bolivia, Chile and Argentina are high (4,500 to 6,900 m or 14,800 to 22,600 ft) and cold, but the relative lack of precipitation prevents snow from accumulating into glaciers. This is because these peaks are located near or in the hyperarid Atacama Desert.

Glacial geology

Diagram of glacial plucking and abrasion Arranque glaciar-en.svg
Diagram of glacial plucking and abrasion
Glacially plucked granitic bedrock near Mariehamn, Aland Islands PluckedGraniteAlandIslands.JPG
Glacially plucked granitic bedrock near Mariehamn, Åland Islands

Glaciers erode terrain through two principal processes: abrasion and plucking.

As glaciers flow over bedrock, they soften and lift blocks of rock into the ice. This process, called plucking, is caused by subglacial water that penetrates fractures in the bedrock and subsequently freezes and expands. This expansion causes the ice to act as a lever that loosens the rock by lifting it. Thus, sediments of all sizes become part of the glacier's load. If a retreating glacier gains enough debris, it may become a rock glacier, like the Timpanogos Glacier in Utah.

Abrasion occurs when the ice and its load of rock fragments slide over bedrock and function as sandpaper, smoothing and polishing the bedrock below. The pulverized rock this process produces is called rock flour and is made up of rock grains between 0.002 and 0.00625 mm in size. Abrasion leads to steeper valley walls and mountain slopes in alpine settings, which can cause avalanches and rock slides, which add even more material to the glacier.

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.

The rate of glacier erosion varies. Six factors control erosion rate:

When the bedrock has frequent fractures on the surface, glacial erosion rates tend to increase as plucking is the main erosive force on the surface; when the bedrock has wide gaps between sporadic fractures, however, abrasion tends to be the dominant erosive form and glacial erosion rates become slow. [43]

Glaciers in lower latitudes tend to be much more erosive than glaciers in higher latitudes, because they have more meltwater reaching the glacial base and facilitate sediment production and transport under the same moving speed and amount of ice. [44]

Material that becomes incorporated in a glacier is typically carried as far as the zone of ablation before being deposited. Glacial deposits are of two distinct types:

Larger pieces of rock that are encrusted in till or deposited on the surface are called "glacial erratics". They range in size from pebbles to boulders, but as they are often moved great distances, they may be drastically different from the material upon which they are found. Patterns of glacial erratics hint at past glacial motions.

Moraines

Glacial moraines above Lake Louise, Alberta, Canada MorainesLakeLouise.JPG
Glacial moraines above Lake Louise, Alberta, Canada

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.

The term moraine is of French origin. It was coined by peasants to describe alluvial embankments and rims found near the margins of glaciers in the French Alps. In modern geology, the term is used more broadly, and is applied to a series of formations, all of which are composed of till. Moraines can also create moraine dammed lakes.

Drumlins

A drumlin field forms after a glacier has modified the landscape. The teardrop-shaped formations denote the direction of the ice flow. Drumlins LMB.svg
A drumlin field forms after a glacier has modified the landscape. The teardrop-shaped formations denote the direction of the ice flow.

Drumlins are asymmetrical, canoe shaped hills made mainly of till. Their heights vary from 15 to 50 meters and they can reach a kilometer in length. The steepest side of the hill faces the direction from which the ice advanced (stoss), while a longer slope is left in the ice's direction of movement (lee).

Drumlins are found in groups called drumlin fields or drumlin camps. One of these fields is found east of Rochester, New York; it is estimated to contain about 10,000 drumlins.

Although the process that forms drumlins is not fully understood, their shape implies that they are products of the plastic deformation zone of ancient glaciers. It is believed that many drumlins were formed when glaciers advanced over and altered the deposits of earlier glaciers.

Glacial valleys, cirques, arêtes, and pyramidal peaks

Features of a glacial landscape Glacial landscape.svg
Features of a glacial landscape

Before glaciation, mountain valleys have a characteristic "V" shape, produced by eroding water. During glaciation, these valleys are often widened, deepened and smoothed to form a "U"-shaped glacial valley or glacial trough, as it is sometimes called. [45] The erosion that creates glacial valleys truncates any spurs of rock or earth that may have earlier extended across the valley, creating broadly triangular-shaped 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.

Typically glaciers deepen their valleys more than their smaller tributaries. Therefore, when glaciers recede, the valleys of the tributary glaciers remain above the main glacier's depression and are called hanging valleys.

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.

Roches moutonnées

Passage of glacial ice over an area of bedrock may cause the rock to be sculpted into a knoll called a roche moutonnée, or "sheepback" rock. Roches moutonnées may be elongated, rounded and asymmetrical in shape. They range in length from less than a meter to several hundred meters long. [46] Roches moutonnées 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 rock fragments loose and carries them away from the downstream side via plucking.

Alluvial stratification

As the water that rises from the ablation zone moves away from the glacier, it carries fine eroded sediments with it. As the speed of the water decreases, so does its capacity to carry objects in suspension. The water thus gradually deposits the sediment as it runs, creating an alluvial plain. When this phenomenon occurs in a valley, it is called a valley train. When the deposition is in an estuary, the sediments are known as bay mud.

Outwash plains and valley trains are usually accompanied by basins known as "kettles". These are small lakes formed when large ice blocks that are trapped in alluvium melt and produce water-filled depressions. Kettle diameters range from 5 m to 13 km, with depths of up to 45 meters. Most are circular in shape because the blocks of ice that formed them were rounded as they melted. [47]

Glacial deposits

Landscape produced by a receding glacier Receding glacier-en.svg
Landscape produced by a receding glacier

When a glacier's size shrinks below a critical point, its flow stops and it becomes stationary. Meanwhile, meltwater within and beneath the ice leaves stratified alluvial deposits. These deposits, in the forms of columns, terraces and clusters, remain after the glacier melts and are known as "glacial deposits".

Glacial deposits that take the shape of hills or mounds are called kames . Some kames form when meltwater deposits sediments through openings in the interior of the ice. Others are produced by fans or deltas created by meltwater. When the glacial ice occupies a valley, it can form terraces or kames along the sides of the valley.

Long, sinuous glacial deposits are called eskers . Eskers are composed of sand and gravel that was deposited by meltwater streams that flowed through ice tunnels within or beneath a glacier. They remain after the ice melts, with heights exceeding 100 meters and lengths of as long as 100 km.

Loess deposits

Very fine glacial sediments or rock flour is often picked up by wind blowing over the bare surface and may be deposited great distances from the original fluvial deposition site. These eolian loess deposits may be very deep, even hundreds of meters, as in areas of China and the Midwestern United States of America. Katabatic winds can be important in this process.

Isostatic rebound

Isostatic pressure by a glacier on the Earth's crust Glacier weight effects LMB.png
Isostatic pressure by a glacier on the Earth's crust

Large masses, such as ice sheets or glaciers, can depress the crust of the Earth into the mantle. [48] 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.

A geomorphological feature created by the same process on a smaller scale is known as dilation-faulting. It occurs where previously compressed rock is allowed to return to its original shape more rapidly than can be maintained without faulting. This leads to an effect similar to what would be seen if the rock were hit by a large hammer. Dilation faulting can be observed in recently de-glaciated parts of Iceland and Cumbria.

On Mars

Northern polar ice cap on Mars Mars north pole.jpg
Northern polar ice cap on Mars

The polar ice caps of Mars show geologic evidence of glacial deposits. The south polar cap is especially comparable to glaciers on Earth. [49] Topographical features and computer models indicate the existence of more glaciers in Mars' past. [50]

At mid-latitudes, between 35° and 65° north or south, Martian glaciers are affected by the thin Martian atmosphere. Because of the low atmospheric pressure, ablation near the surface is solely due to sublimation, not melting. As on Earth, many glaciers are covered with a layer of rocks which insulates the ice. A radar instrument on board the Mars Reconnaissance Orbiter found ice under a thin layer of rocks in formations called lobate debris aprons (LDAs). [51] [52] [53] [54] [55]

The pictures below illustrate how landscape features on Mars closely resemble those on the Earth.

See also

Notes

  1. Post, Austin; LaChapelle, Edward R (2000). Glacier ice. Seattle: University of Washington Press. ISBN   978-0-295-97910-6.
  2. National Geographic Almanac of Geography, 2005, ISBN   0-7922-3877-X, p. 149.
  3. Brown, Molly Elizabeth; Ouyang, Hua; Habib, Shahid; Shrestha, Basanta; Shrestha, Mandira; Panday, Prajjwal; Tzortziou, Maria; Policelli, Frederick; Artan, Guleid; Giriraj, Amarnath; Bajracharya, Sagar R.; Racoviteanu, Adina. "HIMALA: Climate Impacts on Glaciers, Snow, and Hydrology in the Himalayan Region". Mountain Research and Development. International Mountain Society. hdl:2060/20110015312.
  4. Simpson, D.P. (1979). Cassell's Latin Dictionary (5 ed.). London: Cassell Ltd. p. 883. ISBN   978-0-304-52257-6.
  5. "Glossary of Glacier Terminology". USGS. Retrieved 2017-03-13.
  6. "Retreat of Alaskan glacier Juneau icefield". Nichols.edu. Retrieved 2009-01-05.
  7. "Glossary of Meteorology". American Meteorological Society. Archived from the original on 2012-06-23. Retrieved 2013-01-04.
  8. Department of Geography and Geology, University of Wisconsin (2015). "Morphological Classification of Glaciers" (PDF). www.uwsp.edu/Pages/default.aspx.
  9. "Sea Level and Climate". USGS FS 002-00. USGS. 2000-01-31. Retrieved 2009-01-05.
  10. "Types of Glaciers". National Snow and Ice Data Center. Archived from the original on 2010-04-17.
  11. Bindschadler, R.A.; Scambos, T.A. (1991). "Satellite-image-derived velocity field of an Antarctic ice stream". Science . 252 (5003): 242–46. Bibcode:1991Sci...252..242B. doi:10.1126/science.252.5003.242. PMID   17769268.
  12. "Description of Ice Streams". British Antarctic Survey. Archived from the original on 2009-02-11. Retrieved 2009-01-26.
  13. "What types of glaciers are there? | National Snow and Ice Data Center". nsidc.org. Retrieved 2017-08-12.
  14. 1 2 Lorrain, Reginald D.; Fitzsimons, Sean J. (2017). "Cold-Based Glaciers". In Singh, Vijay P.; Singh, Pratap; Haritashya, Umesh K. (eds.). Encyclopedia of Snow, Ice and Glaciers. Encyclopedia of Earth Sciences Series. Springer Netherlands. pp. 157–161. doi:10.1007/978-90-481-2642-2_72. ISBN   978-90-481-2641-5.
  15. Boulton, G.S. [1974] "Processes and patterns of glacial erosion", (In Coates, D.R. ed., Glacial Geomorphology. A Proceedings Volume of the fifth Annual Geomorphology Symposia series, held at Binghamton, New York, September 26–28, 1974. Binghamton, NY, State University of New York, pp. 41–87. (Publications in Geomorphology))
  16. "What causes the blue color that sometimes appears in snow and ice?". Webexhibits.org. Retrieved 2013-01-04.
  17. Benson, C.S., 1961, "Stratigraphic studies in the snow and firn of the Greenland Ice Sheet", Res. Rep. 70, U.S. Army Snow, Ice and Permafrost Res Establ., Corps of Eng., 120 pp.
  18. "Glacier change and related hazards in Switzerland". UNEP. Retrieved 2009-01-05.
  19. Paul, Frank; Kääb, Andreas; Maisch, Max; Kellenberger, Tobias; Haeberli, Wilfried (2004). "Rapid disintegration of Alpine glaciers observed with satellite data" (PDF). Geophysical Research Letters. 31 (21): L21402. Bibcode:2004GeoRL..3121402P. doi:10.1029/2004GL020816.
  20. "Recent Global Glacier Retreat Overview" (PDF). Retrieved 2013-01-04.
  21. Greve, R.; Blatter, H. (2009). Dynamics of Ice Sheets and Glaciers. Springer. doi:10.1007/978-3-642-03415-2. ISBN   978-3-642-03414-5.
  22. W.S.B. Paterson, Physics of ice
  23. Clarke, Garry K.C. (1987). "A short history of scientific investigations on glaciers". Journal of Glaciology. Special issue (S1): 4–5. Bibcode:1987JGlac..33S...4C. doi:10.3189/S0022143000215785.
  24. "Moulin 'Blanc': NASA Expedition Probes Deep Within a Greenland Glacier". NASA. 2006-12-11. Retrieved 2009-01-05.
  25. "Glaciers". www.geo.hunter.cuny.edu. Archived from the original on 2014-02-22. Retrieved 2014-02-06.
  26. T. Strozzi et al.: The Evolution of a Glacier Surge Observed with the ERS Satellites (pdf, 1.3 Mb)
  27. "The Brúarjökull Project: Sedimentary environments of a surging glacier. The Brúarjökull Project research idea". Hi.is. Retrieved 2013-01-04.
  28. Meier & Post (1969)
  29. "Seasonality and Increasing Frequency of Greenland Glacial Earthquakes" Archived 2008-10-07 at the Wayback Machine , Ekström, G., M. Nettles, and V.C. Tsai (2006) Science, 311, 5768, 1756–1758, doi : 10.1126/science.1122112
  30. 1 2 "Analysis of Glacial Earthquakes" Archived 2008-10-07 at the Wayback Machine Tsai, V. C. and G. Ekström (2007). J. Geophys. Res., 112, F03S22, doi : 10.1029/2006JF000596
  31. Summerfield, Michael A. (1991). Global Geomorphology. p. 269.
  32. Easterbrook, D.J. (1999). Surface Processes and Landforms (2 ed.). New Jersey: Prentice-Hall, Inc. p. 546. ISBN   978-0-13-860958-0.
  33. "Glossary of Glacier Terminology". Pubs.usgs.gov. 2012-06-20. Retrieved 2013-01-04.
  34. Grunewald, p. 129.
  35. "C.D. Ollier: Australian Landforms and their History, National Mapping Fab, Geoscience Australia". Ga.gov.au. 2010-11-18. Archived from the original on 2008-08-08. Retrieved 2013-01-04.
  36. Kincaid, Joni L.; Klein, Andrew G. (2004). Retreat of the Irian Jaya Glaciers from 2000 to 2002 as Measured from IKONOS Satellite Images (PDF). Portland, Maine, USA. pp. 147–157. Retrieved 2009-01-05.
  37. "Hawaiian Glaciers Reveal Clues to Global Climate Change". Geology.com. 2007-01-26. Archived from the original on 2013-01-27. Retrieved 2013-01-04.
  38. "French Colonies – Crozet Archipelago". Discoverfrance.net. 2010-12-09. Retrieved 2013-01-04.
  39. Collins, Henry Hill; Europe and the USSR; p. 263. OCLC   1573476
  40. "Yukon Beringia Interpretive Center". Beringia.com. 1999-04-12. Archived from the original on 2012-10-31. Retrieved 2013-01-04.
  41. "Earth History 2001" (PDF). July 28, 2017. p. 15. Archived from the original (PDF) on March 3, 2016. Retrieved July 28, 2017.
  42. "On the Zoogeography of the Holarctic Region". Wku.edu. Retrieved 2013-01-04.
  43. Dühnforth, Miriam; Anderson, Robert S.; Ward, Dylan; Stock, Greg M. (2010-05-01). "Bedrock fracture control of glacial erosion processes and rates". Geology. 38 (5): 423–426. Bibcode:2010Geo....38..423D. doi:10.1130/G30576.1. ISSN   0091-7613.
  44. Koppes, Michéle; Hallet, Bernard; Rignot, Eric; Mouginot, Jérémie; Wellner, Julia Smith; Boldt, Katherine (2015). "Observed latitudinal variations in erosion as a function of glacier dynamics". Nature. 526 (7571): 100–103. Bibcode:2015Natur.526..100K. doi:10.1038/nature15385. PMID   26432248.
  45. Glacial Landforms: Trough
  46. 'Glaciers & Glaciation' (Arnold, London 1998) Douglas Benn and David Evans, pp324-326
  47. "Kettle geology". Britannica Online. Retrieved 2009-03-12.
  48. Casper, Julie Kerr (2010). Global Warming Cycles: Ice Ages and Glacial Retreat. Infobase Publishing. ISBN   978-0-8160-7262-0.
  49. "Kargel, J.S. et al.:Martian Polar Ice Sheets and Mid-Latitude Debris-Rich Glaciers, and Terrestrial Analogs, Third International Conference on Mars Polar Science and Exploration, Alberta, Canada, October 13–17, 2003 (pdf 970 Kb)" (PDF). Retrieved 2013-01-04.
  50. "Martian glaciers: did they originate from the atmosphere? ESA Mars Express, 20 January 2006". Esa.int. 2006-01-20. Retrieved 2013-01-04.
  51. Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346–350
  52. Source: Brown University Posted Monday, October 17, 2005 (2005-10-17). "Mars' climate in flux: Mid-latitude glaciers | SpaceRef – Your Space Reference". Marstoday.com. Archived from the original on December 5, 2012. Retrieved 2013-01-04.CS1 maint: Multiple names: authors list (link)
  53. Richard Lewis (2008-04-23). "Glaciers Reveal Martian Climate Has Been Recently Active | Brown University News and Events". News.brown.edu. Retrieved 2013-01-04.
  54. Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf
  55. Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf

Related Research Articles

Drumlin Elongated hill formed by the action of glacial ice on the substrate

A drumlin, from the Irish word droimnín, first recorded in 1833, and in the classical sense is an elongated hill in the shape of an inverted spoon or half-buried egg formed by glacial ice acting on underlying unconsolidated till or ground moraine. Swarms of drumlins create a landscape which is often described as having a 'basket of eggs topography'.

Moraine Glacially formed accumulation of unconsolidated debris

A moraine is any glacially formed accumulation of unconsolidated glacial debris that occurs in both currently and formerly glaciated regions on Earth, through geomorphological processes. Moraines are formed from debris previously carried along by a glacier and normally consisting of somewhat rounded particles ranging in size from large boulders to minute glacial flour. Lateral moraines are formed at the side of the ice flow and terminal moraines at the foot, marking the maximum advance of the glacier. Other types of moraine include ground moraines and medial moraines.

Glaciology Scientific study of ice and natural phenomena involving ice

Glaciology is the scientific study of glaciers, or more generally ice and natural phenomena that involve ice.

Outwash plain Plain formed from glacier sediment that was transported by meltwater.

An outwash plain, also called a sandur, sandr or sandar, is a plain formed of glacial sediments deposited by meltwater outwash at the terminus of a glacier. As it flows, the glacier grinds the underlying rock surface and carries the debris along. The meltwater at the snout of the glacier deposits its load of sediment over the outwash plain, with larger boulders being deposited near the terminal moraine, and smaller particles travelling further before being deposited. Sandurs are common in Iceland where geothermal activity accelerates the melting of ice flows and the deposition of sediment by meltwater.

Cirque An amphitheatre-like valley formed by glacial erosion

A cirque is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are corrie and cwm. A cirque may also be a similarly shaped landform arising from fluvial erosion.

Glacial motion

Glacial motion is the motion of glaciers, which can be likened to rivers of ice. It has played an important role in sculpting many landscapes. Most lakes in the world occupy basins scoured out by glaciers. Glacial motion can be fast or slow, but is typically around 1 metre/day.

Glacial landform Landform created by the action of glaciers

Glacial landforms are landforms created by the action of glaciers. Most of today's glacial landforms were created by the movement of large ice sheets during the Quaternary glaciations. Some areas, like Fennoscandia and the southern Andes, have extensive occurrences of glacial landforms; other areas, such as the Sahara, display rare and very old fossil glacial landforms.

The Oak Ridges Moraine is a geological landform that runs east-west across south central Ontario, Canada. It developed about 12,000 years ago, during the Wisconsin glaciation in North America. A complex ridge of sedimentary material, the moraine is known to have partially developed under water. The Niagara Escarpment played a key role in forming the moraine in that it acted as a dam for glacial meltwater trapped between it and two ice lobes.

Fluvio refers to things related to rivers and glacial refers to something that is of ice. Fluvio-glacial refers to the meltwater created when a glacier melts. Fluvio-glacial processes can occur on the surface and within the glacier. The deposits that happen within the glacier are revealed after the entire glacier melts or partially retreats. Fluvio-glacial landforms and erosional surfaces include: outwash plains, kames, kame terraces, kettle holes, eskers, varves, and proglacial lakes.

Giants kettle cavity or hole which appears to have been drilled in the surrounding rocks by eddying currents of water bearing stones, gravel and other detrital matter

A giant's kettle, also known as either a giant's cauldron, moulin pothole, or glacial pothole, is a typically large and cylindrical pothole drilled in solid rock underlying a glacier either by water descending down a deep moulin or by gravel rotating in the bed of subglacial meltwater stream.

Plucking (glaciation) glacial quarrying

Plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the erosion and transportation of individual pieces of bedrock, especially large "joint blocks". This occurs in a type of glacier called a "valley glacier". As a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints (cracks) in the bedrock. The freezing and thawing action of the ice enlarges, widens, or causes further cracks in the bedrock as it changes volume across the ice/water phase transition, gradually loosening the rock between the joints. This produces large pieces of rock called joint blocks. Eventually these joint blocks come loose and become trapped in the glacier.

Tunnel valley A U-shaped valley originally cut by water under the glacial ice near the margin of continental ice sheets

A tunnel valley is a large, long, U-shaped valley originally cut under the glacial ice near the margin of continental ice sheets such as that now covering Antarctica and formerly covering portions of all continents during past glacial ages.

U-shaped valley Valleys formed by glacial scouring

U-shaped valleys, trough valleys or glacial troughs, are formed by the process of glaciation. They are characteristic of mountain glaciation in particular. They have a characteristic U shape, with steep, straight sides and a flat or rounded bottom. Glaciated valleys are formed when a glacier travels across and down a slope, carving the valley by the action of scouring. When the ice recedes or thaws, the valley remains, often littered with small boulders that were transported within the ice, called glacial till or glacial erratic.

Withrow Moraine and Jameson Lake Drumlin Field

The Withrow Moraine and Jameson Lake Drumlin Field is a National Park Service–designated privately owned National Natural Landmark located in Douglas County, Washington state, United States. Withrow Moraine is the only Ice Age terminal moraine on the Waterville Plateau section of the Columbia Plateau. The drumlin field includes excellent examples of glacially-formed elongated hills.

Glacial history of Minnesota

The glacial history of Minnesota is most defined since the onset of the last glacial period, which ended some 10,000 years ago. Within the last million years, most of the Midwestern United States and much of Canada were covered at one time or another with an ice sheet. This continental glacier had a profound effect on the surface features of the area over which it moved. Vast quantities of rock and soil were scraped from the glacial centers to its margins by slowly moving ice and redeposited as drift or till. Much of this drift was dumped into old preglacial river valleys, while some of it was heaped into belts of hills at the margin of the glacier. The chief result of glaciation has been the modification of the preglacial topography by the deposition of drift over the countryside. However, continental glaciers possess great power of erosion and may actually modify the preglacial land surface by scouring and abrading rather than by the deposition of the drift.

Overdeepening

Overdeepening is a characteristic of basins and valleys eroded by glaciers. An overdeepened valley profile is often eroded to depths which are hundreds of metres below the deepest continuous line along a valley or watercourse. This phenomenon is observed under modern day glaciers, in salt-water fjords and fresh-water lakes remaining after glaciers melt, as well as in tunnel valleys which are partially or totally filled with sediment. When the channel produced by a glacier is filled with debris, the subsurface geomorphic structure is found to be erosionally cut into bedrock and subsequently filled by sediments. These overdeepened cuts into bedrock structures can reach a depth of several hundred metres below the valley floor.

Kankakee Torrent

The Kankakee Torrent was a catastrophic flood that occurred about 19,000 BP calibrated years ago in the Midwestern United States. It resulted from a breach of moraines forming a large glacial lake fed by the melting of the Late Wisconsin Laurentide Ice Sheet. The point of origin of the flood was from Lake Chicago. The landscape south of Chicago still shows the effects of the torrent, particularly at Kankakee River State Park and on the Illinois River at Starved Rock State Park.

Glaciers on Mars

Glaciers, loosely defined as patches of currently or recently flowing ice, are thought to be present across large but restricted areas of the modern Martian surface, and are inferred to have been more widely distributed at times in the past. Lobate convex features on the surface known as viscous flow features and lobate debris aprons, which show the characteristics of non-Newtonian flow, are now almost unanimously regarded as true glaciers.

The glacial series refers to a particular sequence of landforms in Central Europe that were formed during the Pleistocene glaciation beneath the ice sheets, along their margins and on their forelands during each glacial advance.

References

Further reading