ES 331/767 Glossary

Glossary of Glacial Terms
James S. Aber

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Acheulian: archeologic culture attributed to Homo erectus of old world, 300,000 to 1.5 million years BP.

Altithermal: climatic optimum of mid-Holocene when climate was slightly warmer overall than before or since, also called hypsithermal.

Amino-acid dating: dating of organic materials based on racemization (chemical change) of amino-acids, which is both time and temperature dependent.

Arc of exhumation: geomorphic zone inside and parallel to margin of ancient ice sheet in which preglacial strata have been largely stripped away to expose crystalline bedrock. Large lake/sea basins located within this arc: Great Lakes, Great Slave and Bear Lakes, Baltic Sea, Kattegat, etc.
Bergschrund: large crevasse usually found at head of cirque glacier.
Blytt-Sernander sequence: classic sequence of pollen zones during late glacial and postglacial time of northern Europe, from oldest to youngest: Pre-boreal, Boreal, Atlantic, Subboreal, Subatlantic.
Boreal: refers to high northern latitudes, for example the boreal forest is the conifer (spruce) forest extending across northern Canada and Scandinavia. Austral refers to high southern latitudes.
Carbonate compensation depth: depth in an ocean basin below which rapid solution of calcium carbonate takes place. Little calcareous ooze can accumulate below this depth, which varies from one ocean to another.
Cirque: horseshoe-shaped basin at head of glacial valley, enclosed by high head and side walls, with low lip and smooth basin floor; often containing small lakes or glaciers today in alpine settings.
CLIMAP: stands for "Climate, Long Range Investigation, Mapping and Prediction", a group project to monitor climatic change in ocean cores and to map the climatic patterns.
Dendrochronology: tree-ring dating, using master sequences for particular species within particular regions. Also used for dendroclimatology.
Diamicton: unsorted and unstratified sedimentary deposit of any origin, for example: till, landslide debris, mudflows, turbidites, etc.
Drift: general term refering to any kind of glacially derived deposits. Comes from early idea that most drift was dropped from melting icebergs drifting in a glacial sea.
Drumlin: elongated, streamlined hill molded by glacial deposition or erosion. Usually found in fields containing hundreds of individualdrumlins, located behind major end moraines and parallel to ice flow direction.
Erratic: any kind of rock material that has been transported by ice or water a great distance from its origin and now rests on bedrock of different character, also called exotics.
Esker: long, narrow, high ridge of sand and gravel representing ice-contact deposits of some kind of melt-water stream or delta; generally normal to ice margin, behind major end moraines.
Eustasy: global position and changes in position of sea level.
Exine: resistant outer shell of pollen grain often preserved in sediments and which can be identified to generic level.
Facies: lateral or vertical changes in the character of a sediment or rock unit. Changes in mineralogy, color, texture, fossil content, etc.
Fennoscandian Ice Sheet: Pleistocene ice sheet centered on Norway, Sweden, and Finland, and extended at times into the northern European lowlands.
Firn: old snow which has survived at least one summer melt season, density in the range of 0.4 to 0.5 (see névé).
Fjord: deep, long, steep-sided glacial trough that extends into the sea.
Glaciation/deglaciation/interglaciation: process of growth and spreading of ice sheets and glaciers to cover a major portion of the Earth's land (app. 30% during height of Pleistocene glaciations). Deglaciation is the opposite, the shrinking of ice sheets and glaciers to uncover land areas; the world is presently in an interglaciation in which roughly 10% of the land is ice covered.
Glacier accumulation/ablation: gain of ice mass mainly through snowfall by a glacier; ablation is the loss of mass mainly by melting or calving.
Glacier ice: ice formed from the accumulation and recrystallization of snow, which exhibits past or present flow. Typically has a bluish-green color due to tiny gas bubbles or may be dirty with included sediment. Density 0.5-0.9 g/cc.
Glacier surge: rapid, wavelike movement of ice down a glacier which results in sudden advance of the ice margin. Mass transfer of material from the accumulation zone to the ablation zone with high ice velocities. Occurs cyclically in certain glaciers, but never occurs in others.
Glacio(...): used as a prefix with another term to indicate relationship to glaciers, as in: glaciofluvial = melt-water streams, glaciolacustrine = ice-marginal lakes, glaciomarine = ice-marginal seas, glaciotectonic = ice-induced deformations in bedrock and sediment, etc.
Gumbotill: till which is highly weathered and becomes sticky and plastic when wet.
Holocene (Recent) Epoch: last and still continuing portion of the Quaternary Period. Characterized by wholly modern fossils (all fossils are of modern organisms). Began 10,000 radiocarbon years BP with the end of the last major glaciation.
Ice lobes, fans, domes, etc: dynamic features within large ice sheets which reflect glacier accumulation and ablation, ice temperature, bedrock topography, ice topography, marginal seas, and ice flow:
- Dome - high, central stable portion of ice sheet with low rates of accumulation and slow ice movement.
- Saddle - depression or sag on ice sheet between domes.
- Divide - line across central domes or saddles marking iceshed position.
- Stream - narrow zone extending from dome toward margin in which concentrated, fast ice movement takes place, often developed over subglacial troughs or valleys. Also called fleuve de glâce.
- Lobe - marginal extension of ice stream along broad bedrock trough or valley, may be 100s of km long.
- Tongue - small marginal extension of ice sheet into narrow valleys, generally few km long.
- Fan - coalescence of thin, marginal, ice lobes on land.
- Shelf - portion of ice margin floating on sea or lake, ablation by calving of icebergs into water.
INQUA: International Union for Quaternary Research; international scientific organization for study of Quaternary geology, climate, biology, and anthropology, founded in 1928.
Isostacy: concept of a density/mass equilibrium within the lithosphere that "floats" on the asthenosphere. Changes in mass, such as loading and unloading by ice or water bodies, cause depression or rebound of the lithosphere.
Isotope: form of an element with a certain number of neutrons, for example carbon exists in three isotopes: C¹², C¹³, and C¹⁴. Some isotopes are naturally unstable and spontaneously decay at a fixed rate; other isotopes are stable.
Jökulhlaup: Icelandic term for massive outburst flood of glacial melt water, often associated with a subglacial volcanic eruption.
Kame: hill or terrace deposit of ice-contact, stratified drift laid down in ice-marginal streams or deltas; generally parallel to ice margin.
Laurentide Ice Sheet: Late Wisconsin ice sheet that covered all of eastern and central Canada and extended into the north-central and northeastern U.S.A. It may have joined at times with the Greenland and Cordilleran Ice Sheets.
Little Ice Age: period of expanded alpine glaciers and cooler climate during the 16th through 19th centuries. Corresponds with Maunder solar minimum.
Loess: silt-sized sediment which mantles uplands in deserts and periglacial regions. Represents wind-blown (aeolian) dust deposits.
Maunder minimum: period of solar minimum from A.D. 1645 to 1715, during which sunspots and auroras were much less common and the 11-year sunspot cycle did not exist.
Milankovitch mechanism: mechanism for climatic cycles resulting from changes in latitudinal distribution of solar radiation due to variations in Earth's orbital geometry around the sun.
Moraine: general term refering variously to glacial deposits or landforms. Used in America mainly for glacial landforms of constructional nature, such as end moraine or ground moraine. Used in Europe also to refer to the glacial deposits themselves, as with moraine clay or sand. Also refers to sediment in transport by a glacier, such as medial or lateral moraines. Derived from French word for piles of rubbly deposits in front of glaciers.
Morphologic sequence: refers to a single downstream progression of landforms and stratified drift leading from an ice-contact position to distal river, lake, or sea.
Mousterian: Old World archeologic culture attributed to Neanderthal Man, 50,000 to 100,000 years BP.
Neoglaciation: series of relatively small glacier readvances during the last few thousand years of the Holocene.
Névé: zone of accumulation in high portion of glacier where firn is found.
Nunatak: Eskimo term refering to mountains or lands that protrude through an ice sheet.
Ogives: alternating bands of dirty and clean ice on surface of valley glacier below an ice fall, annual banding formed by summer and winter movement over ice fall, also known as Forbes bands.
Oxygen-isotope ratios: ratio of stable oxygen isotopes in various materials, such as sea water, glacier ice, and fossil shells. Thought to be a reliable indicator of past climatic conditions.
Paleoecology: reconstruction of past environments, especially from a viewpoint of ancient plant and animal life.
Paleo-Indians: earliest well-documented archeologic cultures in North America, 6000-12,000 years BP, characterized by Clovis, Folsom, or other well-made spearpoints, associated with several now-extinct large mammals (i.e. mammoth).
Paleomagnetism: Earth's magnetic field of the past as shown by natural remnant magnetism in rocks; paleomagnetic reversals of polarity are a common feature, and reversals can be used as stratigraphic markers.
Paleosol: ancient or buried soil, often used as a stratigraphic marker for interglaciation.
Palynology: scientific study of pollen, pollen stratigraphy, paleobotany, and paleoclimatology of plants.
Paternoster lakes: chain of small lakes located in successive cirques or rock basins along an alpine glacial valley; may resemble beads on a rosary.
Pelagic: refers to the deep (abyssal) central portion of an ocean basin.
Periglacial: refers to zone or environment surrounding an ice sheet or cap, often characterized by harsh climate.
Permafrost: perennially frozen ground, often containing ice-wedge polygons, pingos, and other unusual features.
Phenology: scientific study of dates of plant growth phenomena, such as flowering or ripening of fruit.
Phylogeny: evolutionary relationship of species.
Pleistocene Epoch: subdivision of the Quaternary Period. Characterized by almost modern fossils (70% fossil mollusks still living organisms), major glaciations of the mid-latitudes, and with associated climatic and environmental changes. Ended roughly 10,000 years BP with the end of the last major glaciation.
Pluvial/interpluvial: period in arid regions much wetter than at present when large freshwater lakes existed. Interpluvials are drier periods (like the present) between pluvials. Pluvials are thought to correspond approximately to major Pleistocene glaciations.
Polynya: open seawater between pack-ice and the land or edge of a glacier, Arctic or Antarctic regions.
Quaternary Period: last period of the geologic time scale, commonly subdivided into Pleistocene and Holocene Epochs. Began 1.6 million years BP and characterized by frequent and rapid environmental changes. The evolution of the genus Homo (man) is probably the single most important development of this period, thus the term Anthropogene is used by some for this period.
Radiometric dating: determination of the age of appropriate materials based on radioactive decay of certain isotopes. Common methods used in Quaternary studies include: C14, fission-track, U series, K-Ar, etc.
Regolith: deeply weathered bedrock produced by prolonged and intense decay of bedrock usually under tropical conditions. Remnants of preglacial regolith found in glaciated regions of Canada and Fennoscandinavia.
Regelation: process of high-pressure melting and refreezing of water at temperatures below 0°C due to pressure changes at base of glacier.
SMOW: stands for "Standard Mean Ocean Water", used as a chemical and isotopic reference standard, for example in oxygen-isotope analysis.
Stade/interstade: glacial advance of brief duration within a glacial stage. An interstade is a brief retreat or minor deglaciation within a glacial stage.
Stage: subdivision of an epoch in the geologic time scale; may represent a glaciation or interglaciation during the Pleistocene, for example the Wisconsin Stage or Sangamon Stage.
Stone/bronze/iron ages: general classification of archeologic cultures based on tool materials, devised in Denmark.
Stratigraphy: scientific classification of rock or sediment strata according to attributes of the strata:
- Lithostratigraphy = Organization of strata into units based on their lithological character.
- Biostratigraphy = Organization of strata into units based on their fossil content.
- Chronostratigraphy = Organization of strata into units based on their age (time).
- Morphostratigraphy = Organization of strata into units based on their surface morphology (landforms).
Stratotype: A specific sequence of sediment or rock, in which a stratigraphic unit or boundary is defined. The stratotype should exhibit the typical characteristics for the stratigraphic unit or boundary. The stratotype serves as a global standard.
Striation (striae): small (mm sized) scatches on bedrock and stones made by glacial scouring, often accompanied by grooves, polish, and fracture marks. Indicators of ice movement direction.
Tephrochronology: dating and stratigraphy of volcanic ash (tephra) beds.
Terrace: benchlike or flat-topped land surface within a major river valley and above the level of the valley floor. Often a series of terraces within a valley form steps on the valley sides. Terraces may be erosional or depositional.
Till: general term refering to any kind of sediment deposited directly from glacier ice with little or no influence by running water; typically unstratified and unsorted; sometimes called boulder-clay. May originate in various manners: lodgement (basal) till is deposited below active ice, ablation till is let down to the ground by melting of stagnant ice, and flow till forms as mudflows off the edge of stagnant ice.
Till fabric: alignment of elongated pebbles within till. Thought to be an indicator of direction of ice movement when till was deposited. Both transverse and parallel fabrics commonly developed.
Transgression/regression: advance of a feature (sea or ice) over the land. Regression is the opposite, the retreat of a feature from the land.
Turbidite: deposit of sediment from a turbidity current. Such currents are dense, muddy suspensions produced on steep slopes in lakes or seas by slumping and sliding of soft sediment. Turbidites usually indicate conditions of rapid sedimentation in unstable environments.
Varves: glaciolacustrine laminations deposited as seasonal couplets (summer and winter); each couplet represents one year, and varve sequences can be used for dating purposes.
Ventifact: facetted or triangular-shaped stone formed by sand-blasting in strong winds, often polished to a high degree.
Vistulian/Saale/Elster glaciations: traditional sequence of glacial stages in northern Europe.
Wisconsin/Illinoian/Kansan/Nebraskan glaciations: traditional sequence of glacial stages in central North America.
Würm/Riss/Mindel/Günz glaciations: traditional sequence of glacial stages in Alps of central Europe.

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© by J.S. Aber (2020).