Term
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Definition
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Accumulation Area Ratio
The area of the glacier at the end of the summer, divided by the area of the whole glacier. The higher AAR, the healthier the glacier.
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Definition
| Unorganized debris on the glacier surface |
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Definition
| Rate of increase of net mass balance with altitude. The larger the activity index, the greater is the anual volume of ice that must be transported across the firn line by glacier flow. |
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Definition
The property of ice that causes the deformation rate to differ, depending on the direction of applied stress.
It mainly results from the stress loading history, which can orient individual ice crystals. |
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Definition
| A sharp and sometimes jagged ridge formed by the intersection of two cirques. |
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Definition
| The movement of ice relative to the substrate, either through basal sliding or through bed deformation of a soft sedimentary substrate (till), or both. |
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Definition
| A large crevasse that separates the flowing ice from the nearly stagnant ice mass above. Often it runs clear across the head of teh glacier, where it constitutes a late-summer obstacle to mountaineers when snow bridges have melted away. |
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Definition
| A sausage-shaped block of less ductile material separated by a short distance from its neighbours within a more ductile medium. Normally form perpendicular to the maximum compressive stress. |
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Definition
| The process of the detachment of blocks of ice from a glacier into water. |
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Definition
| Bowl shaped feature at the head of a glacial valley. They have steep headwalls and a low threshold of rock or moraine. Formed as a result of glacial erosion high on a mountainside, and often containing a rock basin with a tarn. |
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Definition
| A high level pass formed by glacial breaching of an arete or mountain mass. |
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Term
| Constitutive relationships |
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Definition
| Relates applied stress to deformation rate (also called stress-strain relationship). This relationship is dependent on the rheology of the specific material. |
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Term
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Definition
(internal deformation)
The movement of an ice mass through the deformation of glacier ice |
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Definition
| Form due to differences in glacier velocity. As the parts move at different speeds and directions, shear stresses cause the two sections to break apart, opening the crack of a crevasse all along the disconnecting faces. |
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Term
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Definition
| Long veins of clear ice a few cm wide, formed as a result of fracture and recrystallization of ice under tension without separation of the two walls. Also formed as crevasses come back together. |
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Term
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Definition
Are the most common crevasse type and they form in a zone of extension.
Ice accelerating.
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Term
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Definition
| Form when there is neither extension nor compression. |
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Term
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Definition
Crevasses that form on the periphery of the glacier as a result of frictional stress between the glacier and the valley walls.
The form due to the shear between the middle of the glacier (flowing faster) and the margins.
If flow is not tensional or compressive, marginal crevasses will form as chevron crevasses, pointint at a 45 degree angle upglacier.
During compressional ice flow, marginal crevasses will splay upglacier at anglers greater than 45 degrees.
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Term
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Definition
Form as the glacier flows from an area of lateral containment to one without (ie. valley walls widen or disappear).
This causes glacier to spread laterally, forming crevasses perpendicular to ice flow.
When longitudinal crevasses show great curvature (due to differential rates of lateral expansion), they are called splaying crevasses. |
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Term
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Definition
En echelon
Zones of simple shearing in the marginal areas and between ice-flow units of valley glaciers are commonly defined by these types of crevasses, which are analogous to tension gashes in deformed rocks.
Bergschrund
is a crevasse that divides moving glacier ice below the bergschrund from the stagnant ice above it and may extend to bedrock below. |
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Term
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Definition
| The history of strain on a given structure. Strctural assemblages in glaciers are likely to reflect total strain experienced by teh ice as it has travelled downglacier. |
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Definition
| The physical and chemical changes occuring in sediments b/w the times of deposition and lithification. |
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Term
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Definition
| Smoothly rounded mounds, usually of till deposited underneath a glacier and elongated parallel to glacier flow. Sometimes has a bedrock core. Is formed beneath an actively flowing glacier. |
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Definition
| The resulting ice flow processes caused by the interplay of the physical mechanism causing a glacier to move (gravity) and forces resisting this movement (Friction) |
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Definition
| Debris dispersed throughout the interior of a glacier. It originates either in surface debris that is buried in the accumulation area or falls into crevasses, or in basal debris that is raised by thrusting processes. |
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Term
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Definition
| Separates the ablation and accumulation zones. At this altitude, the amount of new snow gained by accumulation is equal to the amount of ice lost through ablation. |
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Definition
| A narrow, winding ridge of till and outwash deposited by a subsurface meltwater stream of a former glacier. |
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Term
| Extensive and compressive flow |
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Definition
Extensive - occurs as forward velocity of the glacier increases as you go down the glacier
Compressive - occurs as forward velocity of the glacier decreases as one goes down glacier. |
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Definition
| a displacement in a glacier formed by ice fracturing without its walls separating. It can be recognized by the discordance of layers in the ice on either side of the fracture. |
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Definition
| Dense, old snow in which the crystals are partly joined together, but in which the air pockets still communicate with each other. |
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Definition
| Glacier-eroded valleys that have been inundated by the sea. May contain existing glaciers. |
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Definition
| A junction that separates structures rotated in one orientation from structures rotated in a different orientation. Easier to identify on an aerial photograph than in the field. Generally characterized by different flow regimes. |
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Term
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Definition
| Layers of ice that have been deformed into curved forms by flow at depth in a glacier. |
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Term
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Definition
Isoclinal
Similar
Parallel
Chevron
Intrafolial |
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Term
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Definition
Groups of closely spaced, often discontinuous layers of coarse bubble, coarse clear, and fine grained ice, formed as a result of shear or compression at depth in a glacier.
The layered structure of glacier ice generated by flow deformation and recrystallization.
Longitudinal:
Axial Planar: |
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Term
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Definition
| Any action which alters, or tends to alter, a body's state of rest or uniform motion in a straight line. The magnitude of aforce is measured by its effect. |
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Definition
| Top 50m of a glacier, which is not under enough pressure for plastic flow. |
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Definition
Also- Ice Age
A period of time when large areas of the Earth were covered by ice. Numerous glacial periods haveoccurred within the last few million years, and are separated by interglacial periods. |
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Definition
| The extremely fine rock debris that gives a milky color to rivers and a chocolate to green colour to lakes fed by glaciers. |
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Definition
| Debris-laden layer of ice at the bottom of a glacier. |
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Definition
| A rock left perched on an ice pillar by ablation of the pedestal and the surrounding unprotected ice. |
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Definition
| A glacier, usually small, clinging to a steep mountainside. Also any glacier that terminates abruptly at the top of a cliff. |
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Definition
| A tributary valley whose mouth ends abruptly part way up the side of a trunk valley, as a result of teh greater amount of glacial downcutting of the latter. |
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Definition
| Region where the glacier forms. Terminates at the foot. |
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Definition
| A sharp peak of resistant rock left after the surrounding lanscape has been eroded away by glaciers. A horn normally marks the intersection of three or more aretes. Its faces are the headwalls of cirques. |
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Term
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Definition
| Glacier surface features caused by drainage of subsurface water-filled cavities and subsequent colapse of the cavity roof. |
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Definition
| A steep reach of a glacier with a chaotic crevased surfae and rapid rate of flow. Demonstrates very conspicuous evidence of active glacier flow, and tis broken, chaotic surface may be impossible for the most expert mountaineer to traverse. In spite of the name, this feature is still not an ice "fall" in the sense of an avalanche of ice from the terminal of a hanging glacier, which cascades down a mountainside in seconds or minutes. The flow of the underlying ice is accelerated by the steep gradient and constricted channel, while the surface layer of the glacier, unable to accommodate to this change, is broken into crevasses and seracs which are pulled apart by the extending flow at the top. Icefalls separate plateaus or basins, which serve as accumulation zones, from the valley ablation areas of mountain glaciers. |
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Term
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Definition
| An extensive area of interconnected valley glaciers from which the higher peaks rise as nunataks. Not ice cap (completely ice covered area on land, dome with flow from centre) or Ice sheet (a vast, thick layer of ice which inundates a large area of the earth's surface). |
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Definition
| A mass of ice and snow of considerable thickness and covering an area of more tha n50k sq m |
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Definition
| A sudden and sometimes catastrophic flow of water discharged from a glacier. |
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Term
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Definition
| Also known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption b/w the layers. As opposed to turbulent flow. In a glacier, it is regular flow ithout compressive or extending flow (all points move parallel to the bed). |
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Term
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Definition
| Period of time that led to expansion of valley and cirque glaciers world-wide, with their max extents being attained in about 1700-1850 AD in many temperate regions and around 1900 in Arctic regions |
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Term
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Definition
A deposit of rock debris shaped by glacier flow and erosion
Lateral - a ridge of rock debris along the side of a valley glacier
Medial - A long strip of debris on the glacier surface, usually parallel to flow, which originates at the juncture of two glaciers.
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Term
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Definition
| Vertical hole by which a surface meltwater stream enters a glacier. |
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Definition
| A field of snow or firn pillars produced by an advanced stage of sun cup development |
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Term
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Definition
| Land, generally a mountain peak, completely surrounded by glacier ice. |
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Term
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Definition
| The force per unit area that is pushing or pulling on an ice mass in the along-flow direction |
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Term
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Definition
| The force per unit area that is applied perpendicular to a plane. In the case of glacier dynamics, the normal stress is usually considered the stress acting on the ice through vertical loading. |
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Term
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Definition
| Arcuate bands or undulations on the surface of a glacier, convex downstream, usually recurring in a periodic pattern. |
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Definition
| A flat spread of debris deposited by meltwater streams emanating from a glacier. |
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Definition
| A glacier formed at the foot of mountains by the discharge of ice from one or more confined valley glaciers (looks like alluvial fan) |
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Term
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Definition
| Ice begaves like an easily breaking solid until its thickness exceeds 50m. The pressure on ice deeper than this causes plastic flow. At the molecular level, ice consists of stacked layers of molecules with relatively weak bonds between the layers. When the stress of the layer above exceeds the inter-layer binding strength, it moves faster than the layer below. |
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Definition
| Entire block flows in one piece (unlike pudding)... get shear margins as a result. |
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Definition
A glacier that has subfreezing temperatures throughout its mass
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Term
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Definition
| The differences in eleveation and slope b/w the higher and lower parts of the land surface of agiven area. |
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Definition
| The space or crack b/w the edge of the glacier and the adjacent rock wall. It is bounded on one side by ice and on the other by rock. Not to be confused with a bergschrund, which divides two ice masses. |
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Definition
| Thawing and refreezing of ice through application and release of pressure. |
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Term
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Definition
| The altitude at which annual accumulation balances ablation on a ground surface. |
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Definition
| Is the way glacier ice responds (deforms/strains) to applied stress. It is the study of flow. |
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Definition
| A blaock or column of ice formed by intersecting crevasses. Can topple without warning, often house-sized or larger. Found within an icefall, or on ice faces on the lower edge of a hanging glacier. |
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Term
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Definition
The force per unit area that is applied parallel or tangential to a plane. In the case of glacier dynamics, it is most often the force that is applied to glacier ice due to the ice surface slope.
Pure shearing - The sides of the cube remain parallel and perpendicular after the strain event. Directions of greatest compression and extension are constant. The major and minor axes of the deforming ellipse remain constant. All other lines rotate. As in zones of longitudinal compression in mid-glacier, where the strains are coaxial.
The material does not rotate, but is sort of "squished", to use a non-technical term in response to an applied stress. That is, the material uniformly elongates in one direction and uniformly shortes in the perpendicular direction.
Simple shear - One direction remains constant, and everything else rotates relative to it. As at the ice margins, where the strains are non-coaxial.
Involves a rotational strain in which the material moves parallel to agiven axis. Think of a deck of cards being fanned. In simple shear, the axis perpendicular to the shear plane does not shorter. (The deck of cards does not get thinner). |
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Definition
| The lower part of the ablation area of a valley glacier, often shaped like the snout of an animal. |
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Definition
| A poorly drained area of snow or firn which is saturated with water. |
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Definition
| Transient lower margin of winter snow accumulation on a glacier. |
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Term
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Definition
| Techniques for determining the state of strain in rocks generally rely on the rocks possessing some object of known original size or shape. These objects are strain markers. Strain determination depends on the type of marker (several exist) |
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Term
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Definition
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Term
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Definition
| deformation of a solid due to stress |
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Term
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Definition
| A stress which is applied parallel or tangential to a face of a material, as opposed to a normal stress, which is applied perpendicularly. (IE. if a shear stress is applied to the top of a square while the bottom is held in place, the stress results in a strain, or deformation, changing the square into a parallelogram. |
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Definition
| Shallow scratches and grooves carved in bedrock by glacier flow |
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Definition
| A glacier with subfreezing temperatures in most of its mass |
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Definition
| Cupsate hollowsi n a snow or firn surface formed by complex ablation processes during sunny weather. |
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Term
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Definition
| Ice which forms as a result of the freezing of water-saturated snow. It commonly forms at the surface of a glacier between the equilibrium line and the firn line, and gives the glacier additional mass. |
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Definition
| A small lake occupying a hollow formed by glacial erosion |
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Term
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Definition
| A glacier that is at the pressure melting point temperature of ice in most of its mass. |
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Term
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Definition
(or tension)
The stress state leading to expansion; that is, the length of a material tends to increase in tensile direction. The volume of the material stays constant. Is induced by pulling forces, and is the opposite of compressive stress. |
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Definition
| A ridge of debris in front of a glacier terminus marking its maximum stand or position of readvance. |
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Definition
| lower end, snout, of a glacier. |
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Term
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Definition
| A low-angle fault, usually formed where the ice is under compression. Thrusts commonly extend from the bed and are associated with debris and overturned folds. |
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Term
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Definition
| Unsorted debris deposited by a glacier |
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Term
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Definition
| That part of a valley glacier that extends below the firn line. |
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Term
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Definition
| A sharp line on a hillside marking the boundary between well-vegetated terrain that until relatively recently lay under glacier ice. In many areas the most prominent trim-lines date to the Little Iec Age |
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Term
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Definition
| A discontinuity in the annual layering in firn or ice, resulting from a period when ablation cut across successive layers. |
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Term
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Definition
| The stress at which a material begins to deform plastically. At stressed equal or higher than the yield stress the deformation is instantaneous and irreversible. |
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