Virtual Alps Glossary
Virtual Alps Glossary: Alphabetical list
ablation: the process of wastage of snow or ice by melting, sublimation and calving
ablation area/zone: that part of a glacier's surface, usually at lower elevations, over which ablation exceeds accumulation
accumulation: the process of building-up of a pack of snow, refrozen slush, meltwater and firn. Net accumulation for one year is the material left over at the end of the melt-season.
accumulation area: that part of a glacier's surface, usually at higher elevations, on which there is net accumulation of snow, which subsequently turns into firn and then glacier ice. anabatic wind: a wind that flows upvalley over a glacier, caused by warm air rising from the valley sides which have been heated by the sun during the day.
arête: asharp, narrow, often pinnacled ridge, formed as a result of glacial erosion from both sides. (from the French)
basal debris: rock fragments and ground-up bedrock incorporated into the base of a glacier.
Basal ice layer: The layer of ice at the bed of a glacier that is the product of melting and refreezing. It is strongly layered, sheared and incorporates a variable amount of debris. Basal sliding The sliding of a glacier over bedrock, a process usually facilitated by the lubricating effect of meltwater.
Bergschrund: An irregular crevasse, usually running across an ice slope in the accumulation area, where active glacier ice pulls away from ice adhering to the steep mountainside (from the German).
Boulder clay: An English term for till, no longer favoured by glacial geologists.
Braided stream: A relatively shallow stream with many branches that commonly recombine and migrate across a valley floor. Braided streams typically form downstream of a glacier.
calving: the process of detachment of icebergs and smaller blocks of ice from a glacier into water
chattermarks a group of crescent-shaped friction cracks on bedrock, formed by the juddering effect of moving ice.
cirque: an armchair-shaped hollow with steep sides and back wall, formed as a result of glacial erosion high on a mountainside, and often containing a rock basin with a tarn (known as corrie or cwm in Britain) (from the French).
cirque glacier: a glacier occupying a cirque.
col: a high-level pass formed by glacial breaching of an arête or mountain mass (from the French).
cold glacier: a glacier in which the bulk of the ice is below the pressure-melting point and therefore frozen to the bed.
conduit: a drainage tunnel within or at the bed of a glacier.
corrie: a British term for cirque, derived from the Gaelic coire
crag-and-tail: a glacially eroded rocky hill with a tail of till formed down-glacier of it.
crevasse: a deep V-shaped cleft formed in the upper brittle part of a glacier as a result of the fracture of ice undergoing extension. For various types of crevasses refer to longitudinal crevasse, transverse crevasse, en-echelon crevasse and bergschrund.
cross-sectional area: in terms of a river or stream, this is the product of average depth and width.
cryoconite hole: a small cylindrical hole on the surface of a glacier, formed by small patches of debris that absorb more radiation than the surrounding ice, and melt downwards at a faster rate
cwm: a British term for cirque, derived from the Welsh and occasionally used more widely
dead ice: glacier ice which is stagnant, i.e. no longer moving. Typically dead ice is found buried under debris in terminal or lateral moraines after the glacier receded from them. Also the ice of flat glacier tongues may become dead during a phase of glacier recession.
dirt cone: a thin veneer of debris draping a cone of ice up to several metres high, formed because the debris has retarded ablation under it.
discharge: the volume of water passing a particular point on a river per unit time. SI units are m3/s or cumecs. Calculated as the product of mean velocity and cross-sectional area.
drift: a 19th century term, still in use, to describe all unconsolidated deposits associated with glaciers, glacial meltwater and icebergs.
drumlin: A streamlined hillock, commonly elongated parallel to the former ice flow direction, composed of glacial debris, and sometimes having a bedrock core; formed beneath an actively flowing glacier.
end moraine (see terminal moraine)
englacial conduit: A channel, commonly cylindrical, formed within the body of a glacier, carrying water towards the glacier bed or margins. Capture of a stream upglacier commonly leads to their abandonment
englacial debris: Debris dispersed throughout the interior of a glacier. It originates either as surface debris that is buried in the accumulation area or falls into crevasses, or in basal debris that is raised from the bed by thrusting or folding.
englacial stream: a meltwater stream that has penetrated below the surface of a glacier and is making its way towards the bed.
equilibrium line/zone: the line or zone on a glacier's surface where a year's ablation balances a year's accumulation (cf. Firn line). is determined at the end of the ablation season, and commonly occurs at the boundary between superimpoIt sed ice and glacier ice.
erratic: A boulder or large block of bedrock that is being, or has been, transported away from its source by a glacier.
esker: (from the Gaelic): a long, commonly sinuous ridge of sand and gravel, deposited by a stream in a subglacial tunnel.
firn: dense, old snow in which the crystals are partly joined together, but in which the air pockets still communicate with each other. It has a sugary texture (from the German).
fjord: a fjord (from the Norwegian; spelt fiord in North America and New Zealand) is a long, narrow arm of the sea, formed as a result of erosion by a valley glacier
fold: layers of ice (and sometimes debris) that have been deformed into a curved form by flow at depth in a glacier.
foliation: groups of closely spaced, often discontinuous, layers of coarse bubbly, coarse clear and fine-grained ice, formed as a result of shear or of compression at depth within a glacier. The two dominant types are longitudinal and arcuate.
glacial lake outburst flood: during a period of glacier recession, back from a terminal moraine, a lake may form. This lake is impounded by an unstable pile of debris and buried ice. Catastrophic failure of the moraine will result in a devastating flood. Usually associated with high mountain regions such as the Andes and Himalaya.
glacial trough: a glaciated valley or fjord, often characterised by steep sides and a flat bottom, with multiple basins, resulting primarily from erosion by strongly channelled ice.
glacier: a mass of ice, irrespective of size, derived largely from snow, and continuously moving from higher to lower ground.
glacier advance: the forward movement of the snout (toe) of a glacier following successive years of positive mass balance.
glacier recession/retreat: the shrinking of the snout (toe) of a glacier following successive years of negative mass balance. This is usually evident from the recession of the ice margin on land, or calving in the sea, but also from down-wasting.
glacier table: a boulder perched on a pedestal of ice. The boulder protects the ice from ablation during sunny weather. Around the boulder the ice surface ablates and, therefore, is lowered, whereas the boulder remains at the original level. While the pedestal becomes higher and higher in relation to the glacier surface, the sun shines further under the boulder from the south (in the northern hemisphere). Consequently the pedestal gets ablated on its southern side, and the boulder will eventually fall off the pedestal, usually on its southern side (in the northern hemisphere). After this a new cycle of table growth and destruction may begin.
glacier tongue: the long slender part of a valley glacier that is subject to net ablation.
glacierised: the character of land currently covered by glacier ice (cf. Glaciated).
groove: a glacial abrasional form, with striated (q.v.) sides and base, orientated approximately parallel to the ice-flow direction, and commonly up to a few metres wide and deep.
gendarmes: Ice towers such as seracs and penitantes.
glacial (glaciation): Period of time during an ice age when glaciers advance because of colder temperatures. (2) Involving glaciers and moving ice. Usually pertaining to processes associated with glaciers.
glacial budget: The annual relationship between accumulation and wastage. Not equivalent to fluctuations in terminus position.
glacial drift (also see outwash): A general term for all material transported and deposited directly by or from the ice, or by water running off the glacier.
glacial ice: Consolidated, relatively impermeable ice crystal aggregates with a density greater than 0.84.
glacial lake: Proglacial lakes form the angle of the land and the angle of the glacier are opposite or in the superglacial/englacial environment. Enormous quantities of fine particles are transported by glacial meltwater, leading to the milky or cloudy appearance of many glacial lakes. After glacial melting, tarn lakes, kettle lakes and Pater Noster lakes remain.
glacial milk: Term used to describe glacial meltwater which has a light colored or cloudy appearance because of clay-sized sediment held in suspension.
glacial polish: The abrasion of bedrock surfaces by materials carried on the bottom of a glacier. This process leaves these surfaces smooth and shiny.
glacial portal: Cavernous openings in subglacial ice and debris above meltwater streams.
glacial retreat: the backwards movement of the snout of a glacier.
glacial surge: a rapid forward movement of the snout of a glacier. Others describe it as rapid, wavelike downglacial ice movements which cause sudden advances of the ice margin.
glacial trough: Glaciers transform v-shaped stream valleys to u-shaped glacial troughs by erosion.
glacial uplift: Upward movement of the Earth's crust following isostatic depression from the weight of the continental glaciers.
glacier: a large long lasting accumulation of snow and ice that develops on land. Most glaciers flow along topographic gradients because of their weight and gravity. Also defined as: A mass of snow and ice flowing mostly down gradient due to gravity.
glacial deposit: Sedimentary material carried by the glacier and left behind when the ice melts.
glacier karst: Stagnant ice covered by debris with surficial lakes, lakes in buried caverns or tunnels, typically found at the ice/soil or ice/water interface of a retreating glacier.
glacier terminus: Where the glacier ends, the leading edge of the glacier, also called the glacier nose.
glacier trough: Steep U-shaped valley with a flat bottom caused by glacial scour and erosion.
glaciofluvial: Geomorphic feature whose origin is related to the processes associated with glacial meltwater.
glaciology: The study of the physical and chemical propeties of snow and ice.
glaze: A smooth, clear coat of ice on older ice, rock or any other surface.
gleization: A soil formation process that occurs in poorly drained environments. Results in the development of extensive soil organic layer over a layer of chemically reduced clay that takes on a blue color.
gley: Dark gray to black, massive and dense sediment which accumulated slowly in low, wet, poorly drained areas.
grease ice: Thin plates of organized ice crystals on the surface of water.
gumbotill: Highly weathered till which becomes sticky and plastic when wet.
gradient: Elevation divided by ground distance, for example, a fall of one kilometer over two kilometers on the ground would result in a 50% gradient. Any units may be used; many American publications give gradients in feet per mile.
gram: In metric units the weight of one cubic centimeter of water at 20º Celsius and 1 atm.
graupel: Variations in temperature, migration of liquid and vapor water, and pressure of snow cover may result in rounded snow pellets from 2 to 5 mm diameter. Graupel is visually similar to hail, but lacks the banded outward growth pattern of hail.
grooves/grooving: As the glacier moves forward, rocks imbedded in the ice scratch the underlying materials. If small, these linear features are called striations. Grooves are larger features which may be regular or irregular and may be helpful in establishing direction of glacial flow.
ground moraine: A gently rolling ground surface underlain by till deposited beneath a glacier and usually bordered by terminal moraines.
grounding line: The place where a glacier extending into the sea or a lake loses contact with the seafloor and begins to float as an ice shelf. The grounding line may be a place with high sediment accumulation.
Gunz: European glaciation related to North American Nebraskan glaciation.
hanging glacier: Ice moving out of high cirques can carve hanging valleys unconnected to a lower glacial mass on steep slopes.
hanging valleys: Tributary glaciers are often smaller than the main glacier and do not cut as deeply. When the ice melts, these shallower glacial troughs lead into the deeper main trough, leaving hanging valleys. Waterfalls are common features of hanging valleys (e.g. Bridal Veil Falls in Yosemite).
headwall: The steep rock at the top edge of the cirque.
hoarfrost: A light, feathery coating of ice.
horn: A peak or pinnacle thinned and eroded by three or more glacial cirques. The Matterhorn of the Swiss Alps was formed in this manner. Also calld pyramidal peak.
hydrograph: a chart plotting the change in river discharge over time.
hypsithermal: A period of time in the mid-Holocene when climate was generally warmer. Also called the altithermal.
ice: The solid form of water is called ice.
ice age: Reoccuring periods in Earth history when the climate was colder and glaciers expanded to cover larger areas of the Earth's surface.
icebergs: Floating chunks of ice which calved off the glacier 5/6th underwater 1/6th above. Northern hemisphere bergs are fractured off the glacial edge and tend to have jagged tops, while Southern hemisphere bergs have about 60 to 90 meters above the sea and are flat on top because they fractured from the flat topped ice shelves which project out over the Southern oceans. Icebergs can occur in fresh or salt water.
ice blocks: Chunks of the glacier remain as ice blocks after glacial outburst floods which may remain as kettle lakes.
ice breccia: Large angular ice fragments embedded in finer ice or snow record abrupt changes.
ice caps: Smaller ice sheets which cap many islands in the Arctic Ocean and in and near Iceland.
ice cliff: Walls of ice where glaciers meet the sea, such as at the edge of land or the edge of an ice shelf.
ice contact deposit: The multiple types of accumulated stratified sediment left behind when meltwater flows over, within, and at the base of a motionless, melting terminus. See kame, kame terraces and eskers.
ice crystals: Ice crystals are hexagonal in internal structure. The basal plane is weak and permits slip.
ice density: Pure ice density is rarely attained except in individual crystals but is assigned the value of 0.917.
ice fall: The reaction of glacial snow and ice to subglacial changes in gradient. The icefall is broken by crevasses and moves constantly when conditions are favorable. Downglacier from icefalls are ogives.
ice floes: Areas of broken pack ice, chaotically fractured and floating on the near-frozen sea. A great hazard to Arctic explorers is getting stranded or isolated on a floe. The open water gaps between floes are called leads. Where floes jam together, jagged sutures appear due to compression.
ice islands: Bodies of land ice calved from sheet or shelf.
ice quakes: The beginning of the formation of a crevasse or moulin is often accompanied by shaking ice and a hissing or cracking sound.
ice rafted debris: Material carried by floating ice that eventually melts and is deposited on the floor of the sea or a lake.
ice sheets (see continental glaciers): large expanses of ice on a continental scale.
ice shelf: A large flat-topped sheet of ice that is attached to land along one side and floats in an ocean or lake. More ice is added from the flow of ice from land and is removed by calving and/or melting.
ice streams: In glaciers, ice flows in lineaments which, if they encounter other ice streams, do not mix. River inflow streams eventually mix, although they may remain discrete in their early encounter. Ice streams gouge their bases and carry till. The sides of ice streams may be marked by lateral moraines and where two streams flow, there may be medial moraines of till dividing the ice streams. Ice streams may reach terminus; or may melt away before then leaving lobate terminal moraines.
ice tongue: A long, narrow projection of ice which points out for the coastline where a valley glacier flows rapidly into the sea or a lake.
ice-wedge casts: A vertical structure that results from cracks in frozen ground (by means of ice wedging) which are later filled by sediment. They are similar to infilled mudcracks in drying lakes, but usually larger.
Illinoian: North American glaciation related to European Riss glaciation.
imbrication: (see fabric)
insolation: The amount of solar radiation received in a specific area. Equatorial areas receive 2.4 times as much as polar areas.
interglacial periods: Times between recognized advances of the ice. Sea level can be hundreds of feet higher in interglacials than in glacial periods. The present time is the latest interglacial period.
internal deformation: One of the ways glaciers flow is by movement across the faces of the ice crystals that make the glacier.
Isostatic rebound adjustment (see glacial rebound): Up or down warping of the Earth's lithosphere to accommodate for mass being added or removed. Northern Ontario, Canada is rebounding in adjustment to the last glacial retreat 10,000 years ago.
jökulhlaup: Pronounced "Yo-kul-hloip," it refers to a glacial outburst flood.
kame: A low, but steep-sided hill or mound composed of poorly sorted sands and gravels deposited in strata by meltwater plunging into crevasses near the melting edge of an ablating glacier.
kame-terrace: Flat-topped ridges built of stratified sand and gravel deposed by a melt water stream between an ablating glacier or a stagnant ice lobe and a higher wall or lateral moraine. The ridge remains after the ice melts away.
Kansan: North American glaciation related to European Mindel glaciation.
katabatic wind: A wind that flows from a glacier, caused by air cooled by the ice becoming heavier than surrounding air, then draining down-valley.
kettle: A shallow basin or bowl shaped depression formed when a large block of ice is buried in outwash or diamicton during ablation. Upon melting and dewatering of the sediment the hole left by the block may become a kettle-lake or a kettle-depression.
kinematic waves: These ice waves move downglacier and are propagated by increasing glacial thickness. Kinematic waves may move two to six times the velocity of surrounding, thinner ice.
lacustrine: Pertaining to lakes. Lacustrine proglacial deposits usually show confined sorting of fine sized sedimentary particles. They may have dropstones if icebergs once floated in the lake. Other lakes associated with glaciers are supraglacial lakes and kettle lakes.
lag time: the time between peak rainfall and peak discharge. In glacier-fed streams, term lag time is also used to denote the time between peak air temperature and peak discharge.
lateral moraines: A moraine which forms on the side of the ice stream, often where the ice meets the rock wall. Also described as: Piles of loose unsorted rocks along the side margins of a glacier which may fallen there, been pushed there by the ice or dumped from the rounded upper surface of the glacier.
leads: Long, narrow openings or fractures in sea ice.
lens/lenticular: A thick-in-the-middle/thin-at-the-edges geologic deposit in which the surfaces converge together.
loess: Windblown rock flour of the silt size class. Loess ("luss") deposits are widespread, homogeneous, massive and unconsolidated fine grained deposits which blankets much of Illinois' downstate landscape. Isolated loess lenses have been found in Chicago Lake Plain deposits.
marine-based ice sheet: A large mass of ice with its base grounded below sea level.
mass balance: The balance of glacial input (accumulation), throughput (transport), and output (ablation) of snow and ice.
medial moraines: Concentrations of till in septa dividing ice streams deposits as medial moraines after complete ablation. Also described as: Where two mountain glacier lateral moraines unite, a dark band of rock forms along the centerline.
meltwater: Water from melted snow or ice.
melting: An endothermic physical process in which solid ice changes into liquid water (0º C at 1 atm). Absorbs 80 calories/gram latent heat.
Mindel: European glaciation related to North American Kansan glaciation.
moraine: Unsorted till (diamicton) deposited either along the sides (lateral moraine) or the ends of an ablating glacier (end or terminal moraine); or the material below a retreating glacier (ground moraine).
moulin: A vertical shaft at the downslope end of a transverse fissure. Hence the erotic appeal of "Moulin Rouge," of Paris in the 1890s. Water flowing down moulins often makes load roaring sounds.
mountain glaciers: Glaciers which form in the mountains.
Nebraskan: North American glaciation related to European Gunz glaciation.
net balance: The change in the amount of mass of a glacier from one year to the next.
neve: The upper area of accumulation in a glacier where firn is found.
nunatak: An Inuit (Eskimo) word for mountains or lands which protrude through the ice.
ogives *: A series of ice waves or bands of lighter and darker material formed below ice falls in some glaciers. Also called Forbes bands, true band ogives are laid down one per year and represent different flow rates through the steep, narrow ice falls. (see false ogives)
outlet glaciers: Valley glaciers which permit ice to move from accumulation areas through mountainous terrain to the sea.
outwash: Stratified sands and gravels washed out from glaciers by meltwater streams and deposited in the proglacial environment, or beyond the active glacial margin.
outwash plain: Proglacial meltwater deposits unconfined sorted sediments; stream pattern depends upon angle of topography.
paleosol: An ancient or buried soil, often used as a stratigraphic marker for interglacial periods.
pancake ice: Coherent plates of ice that can reach a few meters across and grow from thickened grease ice and resembles pancakes or lily pads.
Pater Noster lakes: A string of glacial lakes along the path of a mountain glacier. After the glacier melts, erosional topographic depressions fill with water. The name comes from the similarity to a string of Catholic Christian prayer beads; the first prayer of which begins "Pater Noster..."
patterned ground: Polygonal or circular ground patterns which develop from contrasting size/color soils in poorly drained areas subject to intensive frost action.
pavement: A rock surface, often eroded or striated, which underlies glacial till and is exposed in sufficient quantity to resemble a sidewalk or open plaza.
periglacial: The area around a glacier often characterized by harsh climate.
permafrost: Soil or rock at or near the ground in Arctic or subarctic regions that has been continuously frozen for a long time.
phase: Physical matter is defined to occur in three phases; solid, liquid and gas.
piedmont glacier: A glacier occurring on the piedmont, the gradually sloping area leading down from a mountain to the plains or to the sea. The Malaspina Glacier is a piedmont glacier. Piedmont glaciers are fed by one or more valley glaciers.
pingo: Large mounds of earth-covered ice which form in a permafrost environment which are found in Alaska, Greenland and Antarctica. Pingos may be up to 70 meters tall and 600 meters diameter. The word was borrowed from the Inuit in 1938 by A.E. Porsild after whom Porsild Pingo in Tuktoyaktuk was named. Pingos have an average life-time of about 1,000 years.
pitch: Used to refer to angle or gradient. "A steep pitch" would therefore mean a high gradient or high angle.
plastic flow: In glaciers, plastic flow in ice begins at 50 meters (165 feet) from the top of the ice surface.
plastic solid: A perfectly plastic solid yields after a critical threshold of stress has been exceeded. Theoretically, the material yields at an infinite rate after that.
plucking: The process of loosening and lifting pieces of rock by a flowing glacier. Meltwater intrudes joints and cracks in the underlying material. The freeze/thaw contraction/expansion series provides the leverage to release large blocks of rock.
Polar plateau: The relatively flat, elevated central region of the East Antarctic Ice Sheet.
portal **: Cavernous openings in subglacial ice and debris above meltwater streams.
precipitation: The process by which crystals form from saturated solutions. In meteorology "precipitation" means rain, drizzle, snow, hail and other solid forms.
proglacial: The area in front of, or just at the outer edge of a glacier.
proglacial ground angle: If the proglacial ground angle and the ice are similar, meltwater flows away. Conversely if the proglacial ground angle and the ice angle are opposite, meltwater fills the resulting topographic low spot.
proglacial lakes (see glacial lakes)
Quaternary: The most recent period of the Cenozoic Era which began about 2 million years ago; the two epochs of the Quaternary include the Holocene (the present epoch) and the Pleistocene, which lasted from about 2 million years ago to about 10,000 years ago.
reach: In both streams and glaciers, stretches of the flowing material which are different from those above and below.
rebound: The upwarping of Earth's crust after additional weight is removed from it. (see subsidence)
recessional moraines: End moraines created during occasionally stabilization of the ice front during retreat.
regelation: The process of localized melting and refreezing of ice, involving no overall change in glacier mass.
relative humidity: actual humidity of a packet of air divided by maximum possible humidity that air can hold. In glaciers, if the relative humidity of a packet of air is high enough that the air reaches the dew point as it cools in contact with the snow or ice, condensation occurs, releasing +AH4- 680 calories/gram of latent heat.
relief: The vertical difference between the surface in valleys and hilltops or the vertical between the base of a glacier and its top.
rheology: The study of flow behavior and characteristics.
rime: Ice deposits formed when supercooled water droplets freeze on contact with an object (deposition).
Riss: European glaciation related to North American Illinoian glaciation.
roches moutonnée **: An Alpine term for a rock knob with one smooth side and one steep side, produced by glacial plucking. They are named "fleecy rocks" in French because they often look like a field of giant stone sheep. Roche moutonnee formations are sometimes called "sheepbacks" in English.
rock knob: Carved by the forward advance of the glacier, these knobs have a smooth side and a plucked side. The glacier flowed from the smooth side over the top and plucked out the rock on the down flow side. Central Park, New York City is full of mica-schist rock knobs. Rock knobs and the associated intra-knob depressions may result in the string of lakes known as Pater Noster lakes after the glacier has melted.
rock flour **: Pulverized rock of the smaller size sediment classes (silts and clays) produced by glacial milling can give outwash streams a milky appearance.
rock glaciers: A mass of rock (talus) held together by ice that moves down gradient like a glacier.
saddle: A depression or sag on the ice sheet between domes.
sandar *: Flat outwash plains caused by glacial melting feature braided streams and sinous sand and gravel bars.
saturation vapor pressure of water: The maximum amount of water vapor needed to keep moist air in equilibrium with a surface of pure water. This is the maximum water vapor the air can hold for any given combination of temperature and pressure. (see relative humidity)
scour: To remove or sweep away material.
sea ice: At temperatures of -2º C (28.5º F), freezes directly from ocean water to a thickness of five meters (15 feet). Loosely packed groups of thin floating ice are called ice floes.
septum/septa: Dividing lines between chambers or compartments (such as nasal sinus). In glaciers, vertical partitions between two ice streams or currents within the ice.
seracs: Unstable ice pinnacles formed by intersecting crevasse planes, usually in areas of fast glacier movement.
sheepback: See roche moutonnée.
sheet flow: Unrestricted glaciers including ice caps and ice sheets flow independently of underlying topography. Friction is greatest between the glacier and its base in this form of flow.
slush limit: The highest point from which runoff occurs.
stratified drift: Sediments laid down by glacial meltwater show unconfined sorting.
streaming flow: Where glaciers are constricted, such as in a valley, the flow may or may not be controlled by underlying topography. Friction is greatest at the center and less towards the margins.
snow density: New fallen snow density is near or less than 0.1. Old snow (corn snow) is up to 0.55. Firn density is 0.55 up to 0.82 where begins glacial ice.
snowfall: The amount of snow which has accumulated since the last observation. Intervals of observation may be measured in any unit of time.
snowfield: The zone of accumulation sometimes a cirque, cwm or corrie; or a large open collecting point between mountains.
snowflake: A six-pointed cluster of ice crystals which fall from a cloud is called a snowflake.
snow line: The lower limit of permanent snow cover, below which snow doesn't accumulate.
snowpack: The total ice and snow on the ground, including fresh and older snow and ice.
solifluction: A slow, viscous, downslope flow of saturated sediment and rock debris especially in areas underlain by frozen ground.
strain: The result of a physical material to stress.
stratified drift: Layered and sorted sediments deposited by meltwater streams or bodies of water adjacent to the ice.
stress: Force applied to an object per its unit area. Subglacial forces on rock are sufficient to fracture it, and are considered to exceed 60,000 pounds per square inch in some places.
striations/stria: Gouges in bedrock or on glacial sediments which record abrasion by the moving glacier. If on pavement, stria may reveal direction of glacial movement.
subglacial: The area below the glacier. Subglacial features include deformed sediments, ice caves, and eskers.
sublimation: An endothermic physical process whereby ice passes directly into the vapor state. Absorbs 720 calories/gram of latent heat. Occasionally meterologists use sublimation for both sublimation and its opposite process, deposition. Sublimation is far more costly in energy than proceeding stepwise through melting then evaporation (80 + 100 + 540 = 720 calories/gram); so it is less effective as an agent of ablation than is melting.
subsidence: The downwarping of Earth's crust due to additional weight (such as a glacier or a transgressing sea) being applied to it.
suncup: A melted bowl-shaped depression in ice due to insolation.
supercooled: Supercooled water remains in the liquid state even though the its temperature is below its freezing point.
supraglacial: The area on top of the glacier which may be snow, ice, rock fragments or covered with soil, plants or forests.
supersaturation: In water, the condition which occurs in the atmosphere when the relative humidity is greater than 100 percent.
surges: Periods of extremely rapid movements in glacial flow.
surface hoar: Deposition of ice crystals on a surface which occurs when the temperature of the surface is colder than the air above and colder than the frost point of that air.
suspended sediment: fine sediment transported in suspension in streams and rivers (usually up to ~2 mm b-axis)
suspended sediment concentration: the weight of fine sediment (mg) in one litre of water. Normally expressed at mg/L.
suspended sediment load: the amount of sediment carried by a river or stream normally expressed as kilograms per seconf (kg/s) or tonnes per day (t/dy) or tonnes per year (t/yr)
tabular iceberg: A flat-topped iceberg, usually formed by breaking off an ice shelf.
tarn lake: After melting, the central depression of a former cirque may hold a tarn lake.
tension: One of the three forces (see compression and shear); in ice, tension creates crevasses.
terminal moraine: A ridge formed by the accumulation of glacial deposits at the point marking the furthest advance of an ablating glacier.
terminus: The end of the glacier. Also called a glacial snout.
terrestrial: Land above sea level.
Tertiary: The geological time period before the Quaternary composed of Paleocene, Eocene, Oligocene, Miocene, and Pliocene.
till: Many writers use till for any glacial deposit. However some define till to mean only sediments composed of a mixture of grain sizes which were deposited directly onto the subglacial landscape during basal melting. (see diamicton)
till plain: A gently irregular plain of till deposited by an actively retreating glacier.
topography: the shape of a landscape, composed of its relief and position of natural and man-made features.
transient snowline: The line separating transient accumulation and ablation areas, also a transient equilibrium line.
transverse fissure: A vertical crevasse in a glacier which runs in an upslope-downslope direction (see moulin)
trimlines: Sharp boundaries in vegetation abundance or community type showing the upper margin of a former glaciation. For example, ferns colonize recently deglaciated areas and conifers show that the area has been deglaciated longer.
truncate: In glaciers, truncated surfaces occur along the sides of valley glaciers, beneath mountain and continental glaciers, and across the tops of sediments previously laid down.
truncated spurs: Triangular hillside features due to glacial erosion of the headlands between two former streams.
tundra: A level to undulating treeless plain characteristic of Arctic and subarctic regions. Depressed by glaciation, the knobby surface has many marshes. It is underlain by dark, mucky soil (gley) and permafrost.
valley glacier: A stream of ice flowing down gradient.
valley train: Outwash confined between two rock walls, moraines or by unmelted ice, ice blocks or calving ablation fields.
velocity: Distance travelled per unit time. SI units are m/s.
wastage area: On a glacier, the terminal end where ablation results in deposition of till and removal of water.
weathering: The process of physical and chemical decomposition which changes earth and rock materials in color, texture, composition, firmness or form. These changes are accomplished by the effects of energy and exposure to water, other fluids and the atmosphere.
whalebacks:Elongated mounds or hills shaped by glacier movement may indicate direction of ice flow.
white-out: A weather condition in which the horizon cannot be identified and there are no shadows. White snow blends everywhere. All you see is white.
Wisconsinan: North American glaciation related to European Wurm glaciation.
Wurm: European glaciation related to North American Wisconsinan glaciation.
zone of ablation: The termini of glaciers where loss of ice occurs through calving, melting or evaporation.
zone of accumulation: The snowfields or cirques of mountain glaciers and the snowfields of continental glaciers are called the zone of accumulation because it is here than new snow falls to nourish the glacier.
zone of fracture: The upper 50 meters of glacial ice is brittle and is carried by the ice below it.
zone of wastage: The area or areas on a glacier where there is a net loss of snow and ice from the glacier.