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Last updated: May 24, 2001 Unless otherwise specified; text, tables, photographs, maps and other
graphics © 1999-2001 Gunnar Ljungstrand


Glossary Glossary

A

Ablation Loss of ice and slow from a glacier, (most often) the biggest part of the "expenses" for a glacier, normally dominated by melting. Ablation is caused primarily by direct sunshine, where the albedo has a great impact, warm air and condensation from humid air. Evaporation of ice, melting due to rain or bed melting due to heat from the Earth's interior (except in volcanic areas) normally play a minor role. The ablation on Scandinavian glaciers varies between roughly 0.5 and 12 m water equivalent during normal years, depending on altitude.

Ablation area The part (normally the lower part) of a glacier where the ablation is larger than the accumulation. It is separated from the accumulation area by the firn line. The cross-section of a glacier in the ablation area is normally convex. The size of the ablation area varies from year to year, larger in years with deficit and smaller in years with surplus.

Abrasion Name for the kind of erosion a glacier performs on its bed, grinding the bedrock down using infrozen stones and rock fragments. Together with plucking abrasion makes a glacier bury itself down in its bed. Abrasion erodes mostly fine material, sand-sized and smaller. The erosion speed varies a lot, depending on the glacier velocity, the amount of infrozen rocks and the hardness of the bedrock, but usually lies between 0.1 and 1 mm/year in Scandinavia.

Accumulation Amassing of snow and ice on a glacier, its "revenue". The largest part of the accumulation consists of snow but rime, rain or meltwater that (re)freezes to ice in colder, lower lying strata can have some impact too, as well as in some cases ice avalanches from other, higher lying, glaciers. In Scandinavia the accumulation lies between 0.5 and 5 m water equivalent during normal years, depending on how maritime or continental the climate is.

Accumulation area The part (normally the upper part) of a glacier where the accumulation is larger thatn the ablation. It is seperated from the ablation area by the firn line. The cross-section of a glacier in the accumulation area is normally concave (except for ice caps). The size of the accumulation area varies from year to year, larger in years with surplus and smaller in years with deficit.

The accumulation area of 
Sulitjelmaisen The accumulation area of Sulitjelmaisen, August 1, 1996. (44 kB)

Advance When a glacier advances, or moves forward. An advance can occur due to colder summer climate, more winter precipitation, or both. Colder summers can result in the glacier tongue immediately starts advancing, because the ice movement then gives a surplus resulting in the front starting to directly advance. Such advances are fairly slow though, with normally 1-20 m per year only. Advances caused by increased ice movement, in its turn caused by increased winter precipitation and/or lower summer temperatures, take more time, since a kinematic wave of ice must mover down to the ice front before the glacier can start to advance. However, such advances are normally much more violent, with advance rates of up to 50-100 m per year or even more. Glacier advances form a special kind of terminal moraine wall, a push moraine, when the ice front bulldozes gravel, rocks, and sometimes trees and bushes together. A particularly violent kind of advance is known as a surge, but no such has occurred in Scandinavia during historic times as far as is known.

Briksdalsbreen, advancing glacier Briksdalsbreen, advancing glacier, June 24, 1999. (113 kB)

Albedo Literally "Whiteness"; how light in color something is. A surface with albedo 1.0 reflects all incoming radiation (totally white), while one with albedo 0.0 absorbs all (totally black), within visible light. Freshly fallen snow has a very high albedo (0.95+), old snow (firn) lower (~0.6), pure glacier ice still lower (~0.4), and dirty snow or ice the lowest (~0.2). This is the reason dirty snow or ice melts faster than pure, and that a snowfall in summer decreases melting significantly as long as any fresh snow is left.

Alluvial cone A halfcone-shaped sediment deposit, normally of fairly coarse material, at the foot of a mountain where a stream comes down. Alluvial cones also exist in areas with no glaciers, e.g. in semideserts.

Alpine Name for terrain with many steep and pointed peaks. The glaciers here are mostly of valley and cirque type. Examples of areas with alpine terrain in Scandinavia are Jotunheimen in Norway and Sarek in Sweden.

Very alpine terraine in
Jotunheimen Very alpine terrain in Jotunheimen, July 30, 1984. (81 kB)

Arête French word for sharp mountain ridge, formed by glacial erosion.

Avalanche Collapse of snow down a slope; primarily happens in winter, but may occur in summer too on galciers. There are several types: loose snow avalanche, compact snow avalanche, bslush avalanche etc. A special form restricted to glaciers is the ice avalanche.

Avalanche cone Cone-formed deposit of crushed ice from ice avalanches, below an ice cliff. If an avalanch cone grows large enough it turns into a regenerated glacier. Smaller deposits of snow from normal avalanches can be termed avalanche cones too.

B

Basal sliding One type of ice movement (the other is plastic flow); quite simply ice moving across its bed. This form of movement, which is the only one that erodes the bed, is only found in temperate and partly in subpolar glaciers. The basal sliding is facilitated and lubricated by a thin film of liquid water between the ice and the rock; this water is formed by pressure melting of ice at zero degrees. The portion basal sliding of the total ice movement varies a lot depending on circumstances, from 0 to 90%. In general maritime glaciers have larger portion of basal sliding.

Basal till Till type with pretty large portion of fine material, frozen into the bed layer of the glacier. The coarser material can be frost shattered boulders and rocks, fallen down onto the upper part of the glacier from a mountain side, buried under more snow and ice, and eventually arriving down at the bottom, but can also be material broken loose directly from the bed by plucking. The finer material comes almost entirely from the bed of the glacier, where it is grinded loose by the coarse material frozen into the ice, something known as abrasion. Due to the lesser amount of coarse in-frozen material at the base (no mountain slopes from which rocks can fall down) even the basal ice on outlet glaciers from ice caps normally till poor.

Bed topography How the topography looks beneath the ice; sometimes it is evenly sloping valleys, but often there is overdeepened basins, precipices and sometimes even whole mountains buried beneath the ice. By looking at the surface topography you can make eduacated guesses as to the looks beneath the ice. A depression with almost flat ice indicates an overdeepened basin, a steeper section with a crevasse zone a rock edge, an area with even slope and few crevasses an even valley, a sudden heavily crevassed area a jutting rock klippa etc. Beneath the top of an ice dome the ice is normally thin. To find out exactly how thick the ice is, you will have to use other methods however isen; seismic echo works, but a specially developed glacier radar is much faster and cheaper to use.

Bergschrund Word of german origin denoting as large, deep crevasse in the upper part of a glacier, between the part of the ice frozen to the rock and the part moving. In winter bergschrunds are often filled in with snow, but the crevasse opens up again in summer. A bergschrund is often both wide and deep, and can be a difficult obstacle for mountaineers, especially towards the end of summer.

Blue ice Other name for glacier ice, which indeed has a very beautiful blue color, when the ice is pure anyway. In tempererate glaciers it only takes a few years for snow to be transformed into blue ice, while it may take several tens of years in polar glaciers.

Braided river System of river arms constantly dividing and rejoining again, formed by water with large amounts of sediment. Glacier rivers often display braided river systems, which in extreme cases can cover the entire valley width as a sandur.

Bre The most common Norwegian word for glacier.

C

Calving Fall of ice blocks from a ice cliff down into a lake or the sea. The term also covers blocks breaking off the lower part of the glacier due to their buoyancy, rising up the surface. At high ice cliffs where the ice does not float the calving happens a little at the time in small collapses, and small icebergs, up to about 10 m in size, float away. At larger calvings tsunami waves are produced, which can be dangerous. At a floating glacier tongue in deep water the calving happens more seldom, but much larger pieces are broken off at each time instead, forming up to several hundred m large icebergs (in Scandinavia). Varying water level (tidewater, hydroelectric dams) causes increased calving. Very intense calving can result in catastrophic retreat.

Catastrophic retreat Very fast retreat, up to several hundred m per year, by a glacier tongue, caused by intense calvning. Most often occurs because of increasing water depth when an ice front retreats into an overdeepened basin, often in conjunction with that the ice tongue starts to float. During catastrophic retreat the ice lake or the inner part of the fiord can become almost brimful with icebergs.

Chisel mark Small (dm-size) curved mark in the bedrock, roughly transversal to the ice movement direction, formed by pressure from infrozen rock fragments in the bottom layer of the glacier. Compare ice groove.

Cirque glacier A glacier of alpine type, lying in a more or less deeply excavated cirque in a mountain side. Cirque glaciers are usually relatively small, with a length/width ratio less than about 2. There are transitory forms towards valley glaciers and ice caps both. A typical cirque glacier is Storsylglaciären.

Cold glacier See polar glacier.

Condensation Water vapor in the air turning into liquid phase at contact with a cold surface, e.g. a glacier. At condensation pretty much latent heat, able to melt snow and/or ice, is liberated, and therefore condensation from humid air can have a fairly large impact on the ablation, in particular for maritime glaciers.

Continental climate Climate characterized by relatively large temperature differences between summer and winter, and relatively low precipitation. Glaciers in areas with continental climate are fairly inactive, with low numbers for accumulation and ablation both, and slow ice movement causing only a few crevasses. Continental glaciers normally react slow to changes. The ablation is primarily caused by direct sunshine.

Crevasse Elongated opening in the surface of a glacier. Crevasses can be from a m to several hundred m long, 1 cm to 10 m wide and up to 30-40 m deep. Crevasses are formed by tension in the upper, brittle part of a glacier when the tensions due to uneven stress passes the ice's ability to stay together. Below a depth of some 30 m the plastic flow closes all crevasses again. There are several different types of crevasses: transverse crevasses are most common, but longitudinal crevasses and bergschrunds also occur. All crevasses except the very largest are normally filled in by snow during winter, but the ice movement opens them (or others between) again in summer. In early summer the crevasses are narrow, but they become wider towards the fall. Crevasses are the without comparison biggest danger at glacier travel - as long as you move on bare ice and you can see them in is not so dangerous (even if you may be forced to detours), but crevasses may hide beneath the snow in the upper parts of a glacier. Perhaps the snow bridge will hold for your weight - perhaps not. For this reason you shoul always be at least three people tied into a rope when travelling on snow-covered glaciers, so that the others can brace for the jerk and later pull up the one who might fall through.

Crevasse on 
Austre Okstindbreen Crevasse on Austre Okstindbreen, July 26, 1997. (75 kB)

Crevasse zone Distinct area on a glacier with uncommonly many crevasses. Is formed e.g. above a precipice or other irregularity in the bed.

Crushed ice Snow-like material, in reality finely crushed glacier ice, the material in avalanche cones created by ice avalanches.

Crushed ice on Fonndalsbreen Crushed ice on Fonndalsbreen, July 28, 1997. (118 kB)

Cumulative net balance The sum of the net balances for a glacier during a series of years; a number showing how the volume of the glacier has changed during the period in question. Is stated in water equivalent evenly distributed across the entire ice surface.

D

Dead ice Ice mass not in movement, which is "dead", stagnant ice. Dead ices are usually formed when glaciers melt away during a warmer climate, when the ice thickness has become so low that the ice movement stops. More and more till is accumulated on the surface as the ice melts away, and finally you often can not see any ice at the surface at all. Because of the insulation the ice melts away slower and slower, but in the end there is no ice left but a layer of dead ice till only. During a retreat sometimes whole secions of ice can disconnect from a glacier tongue, forming dead ices. In a climate where the glaciers are growing snow fields can turn into dead ices, and from there into true glaciers too.

Dead ice pit Hollow, sometimes water-filled and sometimes not, often in glaciofluvial material in a delta or a sandur from the ice age, formed by a large ice block that stuck and became partly buried in glacial material, and which then melted away.

Dead ice till Till deposited from a dead ice. Terrain with dead ice till is often very irregular and undulating. This because of the till cover protecting underlying stagnant ice from melting, but sooner or later the heaps of till colapse down into the hollows formed by melting, and then it melts more on other places instead. The end product is a till layer with very varying thickness. Rogen moraine is a special type of dead ice moraine.

Delta Very gently sloping sediment structure where a river transporting fine material runs out into a lake or into the sea A delta mostly consists of material in sand and silt size. Glacier rivers usually contain so much fine material that large deltas are created relatively quickly.

Density How much something weighs for a certain volume. Expressed in g/cm3 liquid water has a density of some 1.0, while compact ice is somewhat lighter at roughly 0.9. The density of freshly fallen snow varies between about 0.1 and 0.3, wind-packed snow can reach 0.4, while firn lies at 0.4-0.6. White firn ice with lots of air bubbels has about 0.75, while blue glacier ice with few air bubbles has a density of some 0.85. Because of the density differences between different snow and ice layers glaciologists recalculate the values to water equivalent for comparisons.

Dirt cone Between a few dm and a few m high cone-shaped structure of ice, covered by a dirt layer about a cm thick. Because of the darker color dirt on a glacier surface absorbs more solar radiation than the ice around, is warmed up and thus melting down into the ice. More dirt is often collected in the hollows, but when the layer gets thick enough it insulates the ice below from melting instead in the same way as the block in an glacier table, and after a while you get a dirt cone.

Dirt cone on
Pårtejekna Dirt cone on Pårtejekna, August 16, 1994. (103 kB)

Drumlin Elliptical hill of till, elongated in the ice movement direction. Is formed by basal till and often exist is swarms. There are variants lying up- or downstream a rock. Drumlins from current Scandinavian glaciers are rare and small, but drumlins from the ice age can be several km long, up to 1 km wide and 100 m high. A related, much smaller form is fluted moraine.

E

Edge cleft Cleft between a mountain side and a glacier. Different from a bergschrund, an edge cleft is formed by melting; the dark rock absorbs more solar energy than the snow, is warmed up and melts the snow and ice closest to it. Some clefts can form through ice movement and melting both.

Equilibrium line The position the firn line has a year with the same amount of accumulation as ablation.

Erosion Wearing down of rock and earth, caused by glaciers, running water, waves, wind, animals or humans. Glaciers erode their beds with abrasion and plucking, and their sides using frost shattering.

Esker Long undulating ridge of sorted glaciofluvial material, deposited by an ice river in a tunnel beneath the ice. Eskers from the ice age may be up to 50 m high and several tens of km long, but examples from current glaciers are much more modest.

F

Fiord Glacially eroded sea inlet, deeper in its inner part than in the mouth. A U-valley eroded down below sea level, and later filled in by the sea. The fiords in Scandinavia were formed during the ice age, and can be very deep; the deepest, Sognefjorden, is 1307 m deep. In general fiords become narrower and deeper in hard bedrock. A fiord is deepest in its middle part because the erosion was most intense there, due to fastest ice movement. Fiords are much less eroded down at their mouths, but often there lie thick moraine walls there too, making it shallower still.

Firn From German: old snow, snow that has survived a summer. Melting and refreezing during the summer and compacting below higher snow layers cause a recrystallization of the snow. Fragile, branched snow flakes are slowly transformed to larger, rounded snow grains, which are packed much denser. Firn consists of up to a few mm large ice crystals, and has a density of some 0.5. In a tempererate glacier it onlt takes a year for snow to be transformed to firn, while it may take ten years or more on polar glaciers.

Firn ice White opaque continuous ice, still containing many air bubbles, an intermediary state between firn and glacier ice. Firn ice has a density of some 0.7.

Firn line The border line between the accumulation and the ablation area. The firn line lies lower down early in summer and during years with mass surplus, and higher up late in summer and during years with mass deficit. The firn line is the border between bare ice and snow-covered ice, and is normally indicated by a slush zone of varying width.

Fluted moraine Moraine structure, reminiscent of drumlins, but in much smaller scale. Parallel "stripes" of stones and gravel in the ice movement direction, a few m wide and half a m high.

Fluted moraine at 
Argalaijekna Fluted moraine at Argalaijekna, August 8, 1996. (79 kB)

Frost shattering Water trickling into cracks in rock freezes when the temperature dips below 0 degrees, and since ice has a lower density than water the ice exercises a strong pressure against the sides of the crack, enlarging it, and finally a stone or boulder is pried loose from the rock. Mountains next to glaciers are exposed to intense frost shattering due to temperatures constantly shifting between plus and minus temperatures, the constant availability of moisture, and the absence of a protecting layer of earth and vegetation. Frost shattering is the source for almost all surface till on glaciers.

G

Glacial 1.) Adjective: Having something to do with glaciers. 2. Noun: See ice age.

Glacial erosion The erosion performed by glaciers, which digs out U-valleys, cuts of valley spurs, and sharpens mountain ridges into arêtes and peaks into horns.

Glacier Definition: Mass of snow and ice, the largest part of which is on land, and that is in movement. Glaciers are formed where the accumulation is larger than the ablation, that is, where the summer heat is not sufficient to melt all winter snow. This can occur either if the summers are cool, or if there comes large quantities of snow in winter, or in a combination of both. Glaciers in areas with moderate winter precipitation but cool summers are continental, and occur partly near the poles (e.g. Svalbard) or in high mountains (e.g. Eastern Jotunheimen), while glaciers in areas with lots of winter precipitation and warm summers are maritime (e.g. Ålfotbreen). Snow that has survived a summer becomes more coarse-grained, and is called firn. As the firn layers are covered by new layers the pressure increases, and by recrystallization and refreezing the lower firn layers slowly turn to continuous ice, at first white firn ice, and then blue glacier ice. When the mass has attained a thickness of some 15-25 m (depending on temperature) the ice slowly starts to move downslope due to its own weight, and we have a glacier. Glaciers vary a lot in size; the smallest are only a few acres in size, whereas the largest are many millions of km. The thickness varies from some 15 m to more than 4 km, in Scandinavia a little more than 600 m at the most though.

Glacier complex Continuous system of a number of ice streams. Ice stream nets, ice fields and ice caps are examples of different kinds of glacier complexes.

Glacier ice Also called blue ice due to the color. The end product after compacting and refreezing of snow, via firn and firn ice. Glacier ice has a relatively high density, but somewhat lower than fully compact ice, this due to the air bubbles glacier ice contains. A certain thickness is required for the blue color to stand out - small pieces look entirely colorless. Normally 90-95% of the volume of a glacier is blue ice; only 5-10% is snow and intermediary forms. Direct sunshine melts glacier ice very unevenly; the contact surfaces between the ice crystals melt much easier than the crystals themselves. After a few days of sunshine this gives the surface a very small-scale irregular texture where you get a good foothold in up to 30 degrees' slope even without crampons, and where every step is characterized by a crunching sound of crushed ice crystals beneath the boots. Rain on the other hand melts the entire ice surface evenly, and after rain a glacier surface can be extremely slippery.

Glacier ice in Kjenndalsbreen Glacier ice in Kjenndalsbreen, September 16, 1989. (81 kB)

Glacier radar Radar used for echo surveying of glaciers. You run a pattern of profiles and in this way get a map over the ice thickness, which subtracted from a map over the surface topography gives the bed topography. For polar glaciers frequencies of several hundred MHz can be used, but temperate glaciers with freely flowing water inside demand lower frequencies; 5-10 MHz or thereabouts.

Glacier river Water course coming from a glacier. Normally the meltwater contains large amounts of sediment, primarily sunspended fine-grained clay, silt, and sand material, but also a considerable amount of gravel and stones bouncing or rolling along the bed. The water in a glacier river is because of this gray and opaque; the quantity of material varies though. In areas with hard bedrock the water contains only small amounts of sediment, looks milky and is fully drinkable (even if there may be some crunching between the teeth), while where the bedrock is softer it can be virtually mud soup. Because of the large amount of sediment in the water glacier rivers are often braided and almost always form deltas where they run out into the sea or into a lake, as well as often sandurs or alluvial cones on dry land.

Glacier table A glacier table is a boulder resting on an ice pillar. They are formed by large boulders protecting the underlying ice from direct sunshine and thereby decreasing the melting. At the same time the ice surface on the sides melts down faster, and after a while the boulder rests on a pillar of ice. Since it is a melting phenomenon glacier tables only occur in the ablation area. Most glacier tables have ice pillars only a few dm high, but unusually large boulders can have ice pillars several m high. As the melting proceeds the ice pillar gets narrower at the same time as it gets higher, and finally the boulder falls off and the pillar melts away.

Glacier 
table on Mikkajekna Glacier table on Mikkajekna, July 9, 1983. (114 kB)

Glacier tongue The lower part of a glacier, often about the same as the ablation area, with a convex cross-section. Seen from the air or from a mountain peak the similarity in appearance to a tongue can clearly be seen.

Glacier tunnel Tunnel-like opening farthest down on a glacier tongue, where an ice river emerges into the daylight. Glacier tunnels often lead into ice caves, but they are very dangerous, due to the great risk of collapse of quick water inundation. Impressive glacier tunnels occur most often in glaciers which are stable or in retreat, while the water in advancing glaciers normally emerges in a very low (1 dm or so) opening.

Glacier wind A kind of catabatic wind; a cold wind sweeping down a glacier in sunny weather. It is formed because the air is heated up much more over the surrounding area than above the glacier itself, partly due to higher albedo, and partly because almost all solar energy is consumed by melting snow and ice. When the warm air rises from the surroundings cold air flows down the glacier as a replacement. The warmer and sunnier weather, and the larger the glacier, the more powerful glacier wind; in some cases it may reach gale force. The glacier wind normally flows in a fairly thin layer; between 2-10 m is common. Sometimes you can see the glacier wind layer from a distance as a thin zone with quivering air just above the surface.

Glaciofluvial material Sorted somewhat rounded material of stone, gravel and sand sizes deposited by glacial rivers. Deposits from the ice age are being heavily used as gravel pits.

Glaciologist Scientist working in glaciology. In addition, there are amateur glaciologists, like e.g. the author of this site.

Glaciology Literally "Lore about ice". Science branch within Earth science, concerned with ice in all its forms, in particular glaciers, but ice on lakes and at sea as well. Researchers working in glaciology are naturally enough called glaciologists.

H

Holocene The time passed since the end of the ice age. Now, the ice sheet ice sheet didn't melt away all in one instant, but during many thousands of years, but normally the time after 10 000 BC is meant. Compare Pleistocene.

Horn Sharp mountain peak where three or more arêtes join up, formed by glacial erosion.

I

Ice age Also called glacial. Really there have been many ice ages; roughly 20 during the latest 2 2 million years, but usually the latest, which lasted from some 120 000 to 10 000 years ago, is born in mind. An ice age is a period when the Earth's climate turns much colder, probably primarily because of cyclic changes in the Earth's orbit and rotation, and large ice sheets spread out across the Earth. During the height of the latest ice age about three times as large an area was covered by ice as now, and so much water was bound up there that the global sea level was some 120 m lower than now. The warmer periods between the ice ages are called interglacials, and we are now at the end of one such. Even during an ice age colder peiods, stades, alternate with warmer, interstades.

Ice avalanche Larger fall of ice from an ice cliff on a steep glacier. Up to several hundred thousands of tons of ice can crash down at the same time, in some cases many hundreds of m. When the ice falls relatively short distances, a few tens of m or so, it is only crushed coarsely into blocks in decimeter to meter size, but when it falls far it is completely pulverized at impact, into something resembling snow, with a few larger pieces of ice here and there. Ice avalanches bring much more rocks and gravel with them than the continuous movement in a normal icefall, making the ice below much dirtier. Repeated ice avalanches create an avalanche cone consisting of crushed ice below the precipice. If the supply of material is high enough the crushed ice fuses together again into new glacier ice and forms a regenerated glacier. Ice avalanches are very dangerous and have resulted in fatalities in modern time.

Ice block from ice avalanche at Bøyabreen Ice block from ice avalanche at Bøyabreen, June 23, 1999. (90 kB)

Iceberg Piece of glacier ice, broken away from an ice cliff, floating in a lake or in the sea. In Scandinavia icebergs are normally small, in most cases smaller than 10 m, but icebergs with sizes up to a few hundred m occur. Because of the density of the ice most of an iceberg lies below the surface of the water.

Iceberg from 
Isvassbreen Iceberg from Isvassbreen, July 28, 2000. (49 kB)

Ice cap Glacier not lying in any topographical depression, but up on a mountain plateau. Larger ice caps are often glacier complexes with outlet glaciers in all directions. Ice caps are typical for Norway, and have been called "glaciers of Norwegian type". Apart from mounatins with plateaus at high altitude relatively high winter precipitation is needed in order for ice caps to form. Small ice caps are often fairly thin, but the larger examples show the highest ice thickness of all glaciers in Scandinavia and may bury the underlying topography completely. A good example of a larger ice cap is Hardangerjøkulen.

Ramnefjellbreen, ice cap Ramnefjellbreen, ice cap, June 25, 1999. (66 kB)

Ice cave Cave in a glacier; may be formed by crevasses or by meltwater. They are seldom totally dark due to ice being translucent, but are instead filled with a shimmering blue light. They can display fantastic ice formations, often have meltwater streams on the floor and water is dripping everywhere. Ice caves are the most beautiful caves there is, but the most dangerous too, because of the high risk of collapse or flooding by icily cold meltwater. Glacier tunnels often lead into ice caves, but they are the most dangerous of them all.

Ice cave in Alep Pastajekna Ice cave in Alep Pastajekna, August 14, 1994. (42 kB)

Ice cliff Vertical ice front, most often caused by calving. Most ice cliffs form where a glacier tongue extends out into deep (more than a few m) water, in a lake or in the sea. The front becomes steep, since ice lying entirely below water is broken off and floats up to the surface due to the buoyancy caused by its lower density. In Scandinavia ice cliffs can be up to a few km wide, and between 1 anh 70 m high above the water surface. A high ice cliff means that the ice rests on the bottom (that is, it does not float), while a low ice cliff can mean very deep water and a floating ice tongue or a thin ice tongue in shallow water. An ice cliff can also form on a steep glacier, from which ice avalanches go down.

The ice cliff of Austerdalsisen The ice cliff of Austerdalsisen, July 18, 2000. (73 kB)

Ice-cored moraine In continental areas the lateral and terminal moraines of glaciers are often ice-cored, with only a relatively thin layer of till above. Ice-cored terminal moraines are large and high and often form whole complexes with many moraine walls next to each other. Ice-cored moraines in steep slopes may slowly flow downslope as rock glaciers.

Ice crystal Single, continuous unit of ice. In a glacier the size varies from some 0.1 mm in freshly fallen snow to several cm (max: >10 cm) for crystals far down on the glacier tongue. Ice crystals slowly grow at the expense of their smaller neighbors, and large crystals are normally very old.

Large ice crystal from 
Mørkbekkbreen Large ice crystal from Mørkbekkbreen, July 17, 2000. (98 kB)

Ice-dammed lake Type of ice lake, dammed by a glacier tongue; most often it is a side valley being dammed. If the lake has an outflow in another direction, and the water pressure is not enough to lift the ice the lake is stable. Otherwise the water will rise until it either starts to flow over the edge, or the water pressure becomes high enough to lift the ice, letting the water pass below itself. In both cases a jökulhlaup is the result, which can cause much damage downstream. To control ice-dammed lakes drainage tunnels keeping the water level below the critical level have been blasted out.

Ice-dammed lake at Rembesdalsskåki Ice-dammed lake at Rembesdalsskåki, September 30, 2000. (40 kB)

Ice divide Borderline between different ice streams within a glacier complex; imagined line where the ice moves in different directions at either side.

Ice dome Gently sloping dome of snow and ice, from which the glacier ice moves out into all directions. The highest point on an ice cap is often an ice dome, and there the ice thickness normally is quite low.

Ice domes in Folgefonna Ice domes in Folgefonna, June 23, 1986. (49 kB)

Ice edge line A high, transversal, terminal moraine-alike formation, consisting of glaciofluvial material, formed when the ice front stands still for a long time. In Scandinvia there are several massive ice edge lines from the ice age, in particular from Younger Dryas.

Icefall Part of glacier, so criss-crossed by crevasses that there is no continuous surface any more, only isolated ice pillars or in more extreme cases a chaotic jumble of ice towers and loose ice blocks. Occurs due to very fast ice movement caused by steep slope or concentration of ice, and/or very uneven bed. Larger icefalls can be several km wide and more than 1000 m high, with average slopes of between 20 and 35 degrees. The velocity in ice falls is higher than anywhere else in a glacier and can in Scandinavia be up to several hundred m a year. Below icefalls ogives are formed. Extremely steep icefalls are disconnected; that is, the ice really falls down in ice avalanches, often many hundreds of m, pulverizing at impact and forming an avalanche cone or a regenerated glacier below. Smaller falls of ice occur very often in icefalls.

The icefall in Bergsetbreen The icefall in Bergsetbreen, June 22, 1999. (100 kB)

Ice field An intermediate form between an ice cap and an ice stream net. An ice field is characterized by a number of continuous depressions, with nunataks jutting up; peaks and ridges between. A good example is Øst-Svartisen.

Ice front The lowermost part of a glacier tongue. A glacier which is advancing has a higher, steeper and more crevassed front than one in retreat. The front of the latter is normally gently sloping and easy to get onto. The front in a stable glacier is often high and steep, but is usually fairly free of crevasses. The ice front of an advancing glacier can be dangerous, due to constant smaller falls of ice from it.

The ice front of Nigardsbreen The ice front of Nigardsbreen, June 22, 1999. (105 kB)

Ice groove Long groove in bedrock, in the ice movement direction. Is formed by rocks and blocks frozen into the ice scrape the rock. Compare chisel mark.

Ice lake Lake, into which a glacier extends, with drifting icebergs. As might be expected the temperature in an ice lake stays close to 0 degrees the year around.

Storglombreen and the ice lake Storglomvatnet Storglombreen and the ice lake Storglomvatnet, September 28, 2000. (58 kB)

Ice movement The special with a glacier is that the ice in it is in motion; because of its own weight an ice mass starts to slowly move downslope when it has achieved a thickness of 15-20 m. In temperate glaciers the motion has two components: basal sliding and plastic flow. Polar glaciers have the latter component only. Glaciers usually move very slowly, and the velocity in Scandinavian glaciers is between some 10 and a few hundred m a year. The faster the movement, the more crevassed the ice becomes. Small, gently sloping glaciers move the most slowly, large steep glaciers move the fastest. The very highest speeds occur in icefalls. The ice movement varies a lot even within a glacier; faster at the surface than at the bottom and faster in the centerline than at the edges (due to friction). The velocity is normally low high up in the accumulation area, increases downstream to a maximum around the equilibrium line (at even slope), and decreases to a relatively low value at the ice front.

Ice river Stream of meltwater flowing in a tunnel along the glacier bed, sometimes emerging into daylight in a glacier tunnel. Brings with it sediments that are being sorted by the water and deposited as glaciofluvial material, in a delta, a sandur, or in the tunnel itself as an esker.

Ice sheet Ice mass covering a continental-size area of land; millions of km2. Today there is only two ice sheets; in Greenland and in Antarctica, but during the ice age ice sheets covered northern Europe and northern Russia as well as northern North America. In the southern hemisphere the Patagonian ice could perhaps qualify as an ice sheet.

Ice stream Here: logical part of a glacier complex moving down towards the same glacier tongue. Can also mean part of ice sheet, where the ice streams much faster than beside, probably because of much lower friction there (water-saturated marine clay as bed).

Ice stream net Complex system of continuous valley glaciers, with mountains looming high above the ice. Northeastern Jostedalsbreen, around Lodalskåpa, is the only good example in Scandinavia.

Ice thickness How thick the ice is. Ice sheets can be more than 4 km thick, but the largest ice depth measured on glaciers in Scandinavia is somewhat more than 600 m, at Vest-Svartisen.

Interglacial Warmer period between ice ages. The interglacials are roughly a tenth as long as the ice ages only. Right now we are in an interglacial, and some 10 000 years have gone since the end of the last ice age. This means that next ice age should be due pretty soon (in geological terms; within 1000 years), but it is possible human warming-up of the Earth (the greenhouse effect) will stop this.

Interstade Somewhat warmer period within an ice age, when the ice sheets decrease in size, but do not disappear.

Isostatic uplift During the ice age the several km thick ice cover pushed the land down with its weight, and then when it melted away the land started to rise up again, something still happening, with up to 1 cm per year.

J

Jökel Older Norse name for glacier.

Jökulhlaup From Icelandic: Catastrophic drainage of meltwater from an ice-dammed lake (or due to volcanic activity beneath glaciers; not in Scandinavia). If the lake is drained by the water running over the edge the jökulhlaup usually will be of low intensity, with a maximum flow of less than a hundred m3/s but with a duration of up to several weeks, with the water slowly melting out a drainage canyon in the ice. If the water pressure instead lifts up the ice from its bed the lake will be drained much faster, due to the much larger cross-sectional area and the high pressure, and we will get a jökulhlaup of high intensity, with a maximum flow of up to several thousand m3/s, but which may be over in a few hours. The latter type in particular can cause severe damage.

K

Kame Deposit of glaciofluvial material in valley side, created by a tributary stream towards an ice mass in a valley during the end of the ice age.

Kinematic wave Wave of ice moving down a glacier after some time of surplus in the accumulation area. Empirically it has been shown that a kinematic wave moves with about 4 times the speed of the actual ice movement. When a kinematic wave reaches down to the ice front it causes a fast and sudden advance, but if the ablation increases while the wave is on its way down it can disappear before reaching the front.

L

Lateral moraine Type of moraine wall lying along the sides of a glacier tongue. Lateral moraines consist mainly of surface till material, and show how thick the glacier tongue has been before. Where two lateral moraines join up a medial moraine is formed.

LIA Short for Little Ice Age.

Little Ice Age Acronym LIA: Name for the climatic time period between roughly AD 1500-1900. This was a time with significantly colder climate on the Earth than the period before and after, and glaciers worldwide then grew larger than they ever had been since the end of the (real) ice age. The exact time for the maximum varies between different areas - in the Alps the glaciers were at tehir largest in the end of the 17th century, while most in Norway reached their maxima around year 1750. Swedish glaciers reached their largest sizes even later; many around year 1900. In Scandinavia the climate before about year 1500 was warmer than now, and the the glaciers were considerably less extensive than today (e.g. Spørteggbreen, which is pretty significant, did not exist at all then). During the period 1500-1675 it became colder however and the glaciers grew to about same size as today, or slightly larger. Then, at the end of the 17th century the second stage arrived, and during the period up to the mid-1700s most Norwegian glaciers grew larger than they ever had been before during Holocene. More continental glaciers in Norway and Sweden reached their maxima later, during the 19th century, or as late as around year 1900. The most important cause for the LIA is believed to be decreased sunshine due to lower solar activity.

Longitudinal crevasse Crevasse extending along the ice movement direction on a glacier. Occurs wherethe ice is exposed to sideways tension, e.g. where a glacier tongue spreads out if the vally becomes wider.

M

Maritime climate Climate characterized by relatively small temperature differences between summer and winter, and relatively much precipitation. Glaciers in areas with maritime climate are relatively active, with high numbers for accumulation and ablation both, and rapid ice movement causing many crevasses. Maritime glaciers normally react quite fast on changes. The ablation is primarily caused by warm air and condensation.

Mass balance Determination of how high accumulation (winter balance) and ablation (summer balance) a glacier has in a year, calculation of the net balance, and later on cumulative net balance.

Medial moraine String of surface till material along the direction of the glacier's flow. Formed by the lateral moraines, where two glaciers join up into one, separating the ice from the one from the ice from the other, or sometimes downstream from jutting nunataks. Medial moraines only occur in the ablation area, becoming wider and more prominent the lower down you get. When a glacier retreats the large amounts of till in a medial moraine can protect the underlying ice so much that it forms a remaining dead ice long after it has been disconnected from the glacier tongue.

Large medial 
moraine on Rieppejekna Large medial moraine on Rieppejekna from W, August 10, 1986. (59 kB)

Meltwater canyon Canyon-shaped formation in a glacier, caused by streams melting their way down into the surface during surface drainage.

Meltwater canyon on Sarekpaktejekna Meltwater canyon on Sarekpaktejekna, August 6, 1998. (48 kB)

Moraine Transversal wall of till material, formed by a glacier. There are many different kinds of moraines, including lateral moraines, terminal moraines, push moraines, yearly moraines and fluted moraine.

Moulin From French: Vertical more or less circular hole in the ice in the ablation area, normally 0.5-2 m wide and 20-50 m deep. Part of the meltwater drainage system of a glacier; many surface meltwater streams end in a moulin. Moulins are formed when a meltwater stream flows down into a crevasse. The melting widens the crevasse in that particular spot, keeping the hole open when the rest of the crevasse is closed again by the ice movement. Below 40-50 m depth in the glacier the ice is so plastic that all open holes are closed again by the pressure, and the meltwater flowing down into the moulin continues in a complex system of entirely water-filled channels, until it comes down at the bottom and collects in a ice river. Moulins only occur on tempererate and sometimes on subpolar glaciers.

Moulin on Ramnabergsbreen Moulin on Ramnabergsbreen, September 30, 2000. (71 kB)

N

Net balance The difference between the winter balance and the summer balance for a glacier. Positive in years with surplus, negative in years with deficit.

Nunatak Word of Greenlandic origin, meaning maounatin peak, rock or other firm land totally surrounded by glacier ice. Most nunataks in Scandinavia are fairly small, a few ten to a few hundred m in size, but there are nunataks which are real mountains too.

O

Ogives Transversal bands of white and blue-gray ice, respectively, below icefalls. They are a kind of "annual rings" formed due to the mixing of the ice in the icefall. The white bands represent ice having moved down the icefall in winter, having been mixed with fresh snow, while the blue-gray bands are "summer ice" with some dust mixed in.

Outlet glacier Part of glacier complex; separate ice stream or glacier tongue.

Dimdalsbreen, small outlet glacier from ice cap Dimdalsbreen, small outlet glacier from ice cap, July 24, 2000. (54 kB)

Overdeepened basin Depression in the bedrock, eroded out by glaciers, filled with glacier ice, water or sediment. Overdeepened basins now ice-filled would be filled by lakes (or in some cases the sea) if the ice disappeared.

P

Piedmont glacier From French, "mountain foot": glacier spreading out into a wide lobe on the plain below the mountains. There is no glacier of this type in Scandinavia.

Plastic flow A part of the ice movement, and the only one occurring in polar glaciers. Consists of separate ice crystals sliding slightly in relation to each other under the influence of pressure. In this way an ice mass, still being solid and brittle, can deform under the influence of forces lasting a long time. Plastic flow is the reason glaciers can move at different rates in different parts. Since plastic flow is motion within the ice mass only it does not cause any erosion of the bed.

Pleistocene Geologic period, during which repeated ice ages have been the most distinctive characteristic. Is considered to have begun some 1.8 million years ago, ended about 12 000 years ago, at the end of the last ice age, replaced by Holocene, the current period.

Plucking Type of erosion of the bed in tempererate, and to a certain extent in subpolar glaciers. The temperature at the bed is around zero degrees, but the pressure melting ensures there is lesser amounts of liquid water right at the bed. This water seeps into cracks in the bedrock, and at the "lee side" of edges it refreezes due to the locally lower pressure. This frost shattering loosens rock fragments being carried along by the ice movement as basal till. Plucking primarily erodes out coarser fragments, of gravel-size and larger.

Polar glacier Also called cold glacier. Glacier, the temperature of which never rises to zero degrees. Such glaciers mainly occur in high polar regions like northern Greenland or at summit level in very high mountain ranges like the Himalaya. Polar glaciers move through plastic flow only since they are frozen to their beds, normally very slow too, and because of this cause very little erosion on their beds. Because of this the glacier ice in them usually is very pure, but often more white than blue (more reminiscent of firn ice), since a very long time is required for snow to turn into ice in the absence of refreezing. Since polar glaciers never melt the ablation is limited to calving and/or evaporation. There is no polar glacier in Scandinavia.

Pressure melting It is normally said that ice melts at zero degrees Celsius, but in reality this is only true at normal atmospheric pressure. Due to ice having larger volume than liquid water the melting point decreases with increasing pressure. At the pressure caused by three hundred m of ice the melting point lies at -0.2° C. Not a large difference surely, but large enough to melt the bottommost part of the ice into a thin film of liquid water between the ice and the rock. This is very important, since it increases the ice movement by allowing basal sliding. In addition the frost shattering intensifies, causing plucking and increasing the erosion a lot.

Push moraine Narrow and steep terminal moraine wall formed when glaciers advance. The Ice front quite simply pushes a wall of rocks, gravel, earth and possible vegetation forward like a bulldozer. When a glacier advances out into a lake which is not too deep a push moraine of lake sediments can protect the ice from too much calving and facilitate the advance.

Push moraine at Engabreen Push moraine at Engabreen, July 23, 2000. (91 kB)

R

Reaction time The time it takes for a change in the ice movement, e.g. a kinematic wave, to move down to the ice front. The reaction time depends both on how long the glacier is, and on how fast it moves, which in turn is a function of how steeply it slopes and how much the ice is concentrated. On small, short and steep glaciers, as on larger but very steep outlet glaciers from ice caps, the reaction time can be as short as 5 years, while it may be as much as 100 years on long, gently sloping glaciers.

Refreezing Meltwater trickling down into snow or ice with a temperature lower than zero degrees freezes to ice again in the spaces, in this way increasing density. At the same time the temperature in the ice mass is increased as the freezing heat is released, so refreezing happens only until the entirety of the ice mass has attained zero degrees. Refreezing occurs at temperate glaciers in early summer, and at subpola glaciers during the entire season, speeding up the snow's transformation into glacier ice very considerably.

Regenerated glacier Glacier with no accumulation area, fed by ice avalanches from higher lying glaciers. Consists of crushed ice having fused together into new glacier ice, usually quite dirty, due to rocks and gravel torn down by the huge avalanches.

Brenndalsbreen, regenerated glacier Brenndalsbreen, regenerated glacier, June 24, 1999. (82 kB)

Retreat When a glacier withdraws. A glacier never moves backwards - it retreats when the ablation is so large so the ice movement is insufficient to compensate. A retreat can occur due to warmer summer climate, less winter precipitation, or both, but can also be caused by increased calving. Warmer summer temperatures can result in the ice front starting to retreat at once, usually rather slowly though; 1-20 m per year. Somewhat faster and more prolonged retreat is caused by decreased ice movement, which in its turn depends on less winter precipitation and/or higher summer temperatures, and may attain between 20 and 50 m per year. The highest retreat rate occurs at calving in deep water (catastrophic retreat), where it may be up to several hundred m per year.

Rime Meteorological phenomenon where droplets in a cloud freeze directly on a cold surface, e.g. a rock or snow. Rime can stick where snow cannot stay, e.g. on a vertical rock wall, and shows the wind direction when it was deposited, since the small ice crystals are deposited on the windward side. Rime can have a certain significance for the accumulationen on a glacier.

Roche moutonnée From French: Typical glacial land form in bedrock, elongated in the ice movement direction, with a roundish, gently sloping stoss side, formed by abrasion and a steep, irregular lee side, formed by plucking

Rock glacier Unusual glacier type, consisting mostly of boulders and rocks, with ice filling up the spaces in between. Rock glaciers can form when a till rich glacier melts away. As the ice melts away more and more boulders, rocks and gravel is accumulated on the surface, forming an isolating cover protecting the ice below from melting. Rock glaciers display even slower ice movement than normal glaciers, often with less than 1 m/year, but the movement forms typical arcuate ridges on the surface. Ice-cored moraines on steep slopes can sometimes display rock glacier-like movement. In Scandinavia there is only a few rock glaciers.

Rogen moraine After type area at lake Rogen in Sweden. Type of dead ice moraine, characterized by steep 10-50 m high and up to a few km long moraine ridges.

S

Saddle canyon Cleft or canyon, eroded out by meltwater from an ice-dammed lake at the end of the ice age. Saddle canyons normally have steep or even vertical sides, can be more than 100 m deep, but currently have no or very little running water.

Sandur Icelandic word: delta-like deposit, but on land and consisting of coarser material, typically sand, gravel and rocks. Is formed by braided rivers transporting very large amounts of coarse material, deposited where the slope lessens, usually right downstream the ice front. Especially extensive sandurs can be formed at repeated jökulhlaups. Also called Outwash plain.

Shelf ice Type of glacier formed where the snow line lies below the sea level. Shelf ices only occur in the Antarctica (apart from a few small ones on Ellesmere Island), have an almost totally flat upper surface and a vertical up to 100 m high ice cliff, and normally float in deep water. Shelf ices grow by snowfall on the upper surface and contributions by land-based glaciers, and shrink by melting from below and through a certain amount of calving. Icebergs from shelf ices are the largest in the world, and may in some cases be more than 100 km (!) long.

Shore line Horizontal mark in valley side after an earlier higher sea or lake level, e.g. after an ice-dammed lake during the end of the ice age.

Silt Grain fraction where the grains are smaller than the ones in sand but larger than the particles in clay. Silt is very easily eroded, and is the main ingredient in deltas.

Slush zone Area on glacier with waterlogged snow; slush. Normally there is a narrow slush zone around the firn line, but subpolar glaciers often display large areas with slush. Such can be very arduous to move across, particularly if the slush is deeper than a few dm.

Snow field Larger area with snow in summer where the winter snow accumulated unusually thick. Snow fields are normally 1-10 m thick. If they grow due to colder and/or more snowy climate they can turn into dead ices or even glaciers.

Snow line Average altitude of the firn line within an area, during a longer period of time. If the mountains are at least that high there are normally glaciers there. The altitude of the snow line depends on how warm and long the summer is and on how much precipitation in the form of snow comes. Winter temperature (as long as it is below zero) and amount of rain has a much smaller impact. Little snow and a warm summer means a high snow line, in the same way as a lot of snow and cool summers means a low snow line. Where the snow line lies below sea level shelf ices are formed. In Scandinavia the snow line lies between roughly 700 and 2000 asl.

Stade Colder period during an ice age, when the ice sheets increase in size.

Subglacial volcano Volcano lying beneath glacier, occurs e.g. on Iceland. Volcanic eruptions below a glacier very rapidly melts large amounts of ice - up to several km3 in a few weeks, causing very large jökulhlaups. Even when a volcano is not in eruption its large heat flow can melt so much ice that a large crater-shaped depression in the ice forms, to where a part of the glacier drains.

Subpolar glacier Glacier, where not the whole ice mass is warmed up to zero degrees in summer. In principle a glacier where certain parts display polar characteristics and other ones temperate. Subpolar glaciers occur in Scandinavia primarily at higher altitudes and in more continental areas. The surface of a subpolar galcier is warmed up to zero degrees in summer and starts to melt, while it continues to be below zero deeper down in the ice mass and along the bed. Because of this meltwater refreezes deeper down in the ice and all internal drainage is stopped. This leads to surface drainage with many and sometimes large and deeply melted-down meltwater streams on the surface, as well as to large slush zones in snow-covered areas with gentle slope. Subpolar glaciers erode their bed more than polar, but less than temperate ones.

Summer balance Part of mass balance measurement. The amount of ice and snow, in the form of melting, evaporation, condensation, and in some cases calving a glacier loses during a summer, expressed in water equivalent and distributed across the entire glacier surface. A continental glacier can during a cool summer have a summer balance of as little as 0.5 m, whereas it in a maritime glacier a warm summer can be as large as 6 m.

Surface drainage Drainage of meltwater on the surface of a glacier; occurs especially at subpolar glaciers, where low internal temperatures stops internal drainage of meltwater. The water melts itself down into the ice, and sometimes forms meltwater canyons.

Meltwater stream on Ålmajalosjekna Meltwater stream on Ålmajalosjekna, July 30, 1996. (103 kB)

Surface till Type of coarse (mostly stones and boulders, only insignificant amounts of gravel and smaller) till coming from frost-shattered material from mountain sides, ending up on the ice mostly by being dragged along in avalanches. Because of this ice caps are very poor in surface till. Lateral moraines and medial moraines almost entirely consist of surface till material.

Surface topography How a glacier looks on the surface; what the contour lines on a normal map shows. Often you can make qualified guesses as to the bed topography looks from the surface topography.

Surge Phenomenon at certain glaciers: sudden, very violent advance, where the ice front courses ahead between 0.5 and 20 km during a few months to years, with top speeds of often more than 100 m a day (!). During a surge the ice is totally disrupted by crevasses, like in the most savage icefall, even where the slope is gentle and even. It seems like surges are a periodic phenomenon, occurring with a period of between 10 to 100 years at the glaciers exhibiting it. In the time between surges the front of such a glacier is almost entirely inactive, almost a dead ice, slowly wasting away. A surge lowers the ice surface significantly in the upper parts and rises it in the lower; thus the slope lessens. Surges seem to have the following mechanism: The stagnant ice at the front obstructs the ice movement from above, so the upper parts become thicker and thicker, and the pressure and slope increases. At the same time many of the channels for meltwater are blocked, so reservoirs of water are built up. A surge is released when the slope and water pressure attain a critical level. The whole glacier is lifted up on a layer of liquid water, lowering the friction to almost zero, making the ice mass "slide" downwards. At the same time very large amounts of meltwater are released, almost like in a jökulhlaup. When all water has drained out the ice settles down on its bed again, and the extremely rapid movement stops. There seems to be a certain minimum size for the phenomenon to happen; all known surging glaciers are relatively big. No known surging glacier exists in Scandinavia, but they exist e.g. in Iceland and Svalbard.

T

Temperate glacier Glacier, in which the temperature in summer rises to zero degrees in the entire volume. Temperate glaciers are more active and move faster than subpolar or polar glaciers, mostly because they move not only by plastic flow, but through basal sliding as well, since the base is not frozen to the bed. Most maritime glaciers in Scandinavia are temperate. The relatively rapid ice movement makes temperate glaciers usually fairly crevassed, and they react fast on climate changes. They erode their beds a lot too and have lots of till, unless the bedrock is unusually hard. Surface drainage is normally rare on temperate glaciers since there is always some crevasse the meltwater can drain down into.

Terminal moraine Type of moraine wall, consisting of both basal and surface till, formed at the ice front of a glacier, by the coarser till material the carried along by the ice being "unloaded" there, slowly forming a wall. The outermost terminal moraines outside a glacier usually originate from the Little Ice Age. Push moraines and yearly moraines are special kinds of terminal moraines.

Terrace Horizontal ledge in the terrain, above a valley floor. Often is eroded down remnants of a delta, deeposited at a higher water level, e.g. in an ice-dammed lake, or in the sea during the end of the ice age, when the land was burdened down by the ice sheet.

Tidewater glacier Somewhat deceptive term for glacier extending down into the sea, calving icebergs, regardless if there is powerful tides in the area or not.

Till Unsorted angular material of all sizes: boulders, stones, gravel, sand, silt, clay, i a chaotic mess, created by and deposited by glaciers, and an infallible sign of earlier glaciation.

Tributary glacier Smaller glacier joining up with with a larger, where both lateral moraines form a medial moraine.

Trim line Line in the terrain, e.g. in a valley side showing the earlier extent of a glacier, e.g. during the Little Ice Age. Trim lines often are very prominent as a break in the vegetation, but they can also be visible on barren mountain walls as a line between rock with lichens and rock without.

Tsunami wave From Japanese ("harbor wave"): wave in a lake or the sea caused by a sudden shock, e.g. at an earthquake, a volcanic eruption, or an avalanche. Is often erroneously called "tidal wave". Tsunami waves can also form next to glaciers at larger calvings, when ice blocks weighing several thousand tons fall down into the water from a height of several tens of m (or if a block loosens from the underwater part of the ice cliff suddenly emerging on the surface. Different from normal wind-generated surface waves tsunami waves affect the entire water volume, and can move almost undetected at deep water to suddenly rise to great height and surge in across the shore. Normally such waves in Scandinavia are not very large, but on one occasion one claimed a fatality.

Transverse crevasse The most common type of crevasse on a glacier. Transverse crevasses are, like their name suggests, crevasses extending more or less perpendicular to the ice movement direction. They form where the ice is stretched so much that it cracks, mostly because of irregularities in the bed, but on the outside of turns as well. Transverse crevasses are often concentrated into crevasse zones.

U

U-valley Valley with U-profile, i.e. with steep walls but flat bottom, formed by glacial erosion. Only occurs in glaciated or previously glaciated areas. Compare V-valley.

V

V-valley Valley with V-profile, i.e. ravine-shaped valley with steep sides, formed by running water. Compare U-valley.

Valley glacier Glacier of alpine type, formed when a cirque glacier grows out of its cirque and starts to fill up a valley. Valley glaciers are normally elongated, with a length/width ratio usually more than 2, generally are larger than cirque glaciers, but there are some overlap and transitory forms are common. Valley glaciers can be complex, accepting contributions from tributary glaciers. If a number of valley glaciers join up in a complex pattern an ice stream net is formed. A typical valley glacier is Mikkajekna.

W

Warm glacier See temperate glacier.

Water equivalent Since the density of snow and ice varies a lot, between different places but also with depth at the same site, all values in mass balance calculations are converted to water equivalent, that is corresponding depth of liquid water.

Wind channel Groove formed at the edge of glacier, next to a mountain side, if the wind conditions are right. Wind vortices sweep away the snow closest to the mountain and an up to several km long and 10-50 m deep fuurow is created. A wind channel is easily separated from an edge cleft, by that the latter one has shar edges while a wind channel is rounded.

Winter balance Part of mass balance measurement. The amount of ice and snow, in the form of snow precipitation, rimew and refreezing a glacier receives during a winter, expressed in water equivalent and distributed across the entire glacier surface. A continental glacier can during a winter with low precipitation have a winter balance as small as 0.5 m, whereas it at a maritime glacier during a winter with lots of snow may be as large as 6 m.

Y

Yearly moraine Type of terminal moraine that can form when a glacier is undergoing slow retreat. In winter, when the melting is zero, the ice front advances somewhat and pushes out a small moraine wall, in summer the ice retreats some distance, next winter the ice makes another small wall, but not as advanced as the one from the year before, etc. The result is a series of small moraine walls with short and even distances between.

Younger Dryas Very cold period at the end of the ice age, between roughly 10900 and 9400 BC, which both started and ended very abruptly. The melting of the ice sheets stopped up totally during this time, and massive ice edge lines were formed. Science does not yet know exactly what caused this extremely large and fast climate change.


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Last updated: May 24, 2001 Unless otherwise specified; text, tables, photographs, maps and other
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