Glossary

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Ablation How glaciers and ice shelves lose mass. This can be through surface melting and run off, calving icebergs, or melting at the base.
Accumulation How glaciers gain mass, chiefly through precipitation.
Aeolian Processes governed by the wind and wind-blown sand and dust.
APIS Antarctic Peninsula Ice Sheet
Bathymetry Measuring the depth of the world’s oceans. Scientists usually meausure ocean depth with ships that send echos to the sea bed, like a submarine. By using high resolution scanning, they can map the landforms on the sea bed in exquisite detail. See Multibeam Swath Bathymetry below.
Cosmogenic Nuclide Dating This is a technique that provides a measure of the exposure age of a boulder. The exposure age is the length of time since the boulder became exposed at the Earth’s surface, for example, after being deposited by a glacier. Cosmogenic nuclide dating works by analysing minerals within the boulder (such as quartz) for nuclides that are formed when certain particles are bombarded by cosmic rays that originate from supernova explosions throughout the galaxy. The most useful nuclides are radioactive, and Beryllium-10 and Aluminium-26 are used most frequently in dating the exposure age of granitic, quartz-rich erratics.
Diamictite Fully lithified rock containing unsorted grains of all sizes (clay to boulders), originating in this case from glaciers during the Neogene.
Englacial “Within” the ice. For example, englacial hydrological conduits transfer water from the surface to the glacier bed.
Entrain Mechanism by which glaciers incorporate debris into their basal ice layers. Melting and refreezing around debris facilitates transportation and deposition.
Erratic Glacially-transported boulder that is of a different lithology to the immediate bedrock.
Eustatic sea level rise When ice sheets and glaciers melt, they transfer water to the oceans. The increased volume of water in the ocean results in global eustatic sea level rise. This is not to be confused with local isostatic changes in sea level, due to the earth’s crust rebounding after being depressed by the weight of the ice mass upon it.
Firn Snow falls onto glacier surfaces, where the crystals change under the weight of snow above, turning into ice. The intermediate stage of multi-year hard snow is known as firn.
Glacial landsystem A method of mapping and characterising a large region. A landsystem comprises related groups of sediment-landform assemblages, such as moraine or drumlin fields. Theoretically, each landsystem should include a predictable range of surface sediments and landforms, defined by careful analysis of modern systems.
Grounding line “Hydrostatic line” of a tidewater glacier or ice shelf. This is where grounded ice reaches floatation point. Ice beyond the grounding line is subject to tidal flexure (it rises and falls with the tide) and melting from below by warm ocean waters. Floating portions of a tidewater glacier can also cool the sub-ice water and accrete marine ice.
Grounding zone wedge Sedimentary ridge, commonly observed by swath bathymetry on the sea floor. Grounding zone wedges indicate that the grounding line of an ice sheet was positioned at this point during recession, and that it was stationary for long enough to form a significant geomorphological feature.
Holocene The last period of Earth’s history after global deglaciation. The last 10,000 years.
Hyaloclastite Rock composed of tuff and basalt fragments, formed during subglacial volcanic eruptions.
Ice-cored moraine Moraine that has a core of glacier ice. These moraines are formed when englacial and subglacial debris is thrust up towards the surface at the glacier snout, which typically is associated with polythermal glaciers. The debris accumulates on the glacier surface at the snout. Once this debris reaches a certain thickness, it may protect the glacier ice from further ablation. If the glacier retreats, the debris-covered portion of the snout is left behind as an ice-cored moraine.
Ice-rafted debris (IRD) Glaciers erode sediments, and sand and rock fragments become embedded in the glacier ice. In tidewater glaciers that calve icebergs, this sediment is rafted out to sea by icebergs. When the iceberg melts the sediment falls out and settles to the ocean floor, where it is known as ice-rafted debris.
Ice Shelf Thick, permanent, floating sheet of ice that is derived from terrestrial tributary glaciers. The back pressure from an ice shelf stabilises its tributary glaciers, which may be prone to acceleration, recession and retreat if the ice shelf melts away.
Ice shelf collapse Ice shelves on the Antarctic Peninsula have been observed to sequentially collapse during the 20th and 21st Centuries. This has been linked to climate warming; the limit of viability of ice shelves is thought to be an average annual temperature of -9°C. As this isotherm moves southwards, ice shelves north of this point have rapidly disintegrated. Processes of ice-shelf disintegration include long-term thinning from surface and bottom melting, but rapid disintegration occurs along structural lines. Meltwater ponds on the ice shelf surface also encourage disintegration, as they melt through the ice shelf to the bottom, forming lines of weakness along which ice bergs may calve off.
Ice Stream Large outlet glacier moving at an order of magnitude faster than the surrounding ice. May by topographically confined. Ice streams transport 90% of the ice and sediment out of Antarctica. Their behaviour and stability is essential to the health of the ice sheet.
Isostatic uplift When there is a mass on the earth’s crust (such as an ice sheet, or a mountain range), the elastic crust is depressed. When the mass is removed, for example by the ice sheet melting, the crust slowly rebounds, resulting in falling relative sea levels. For example, Scotland is still slowly rising up in response to the removal of the last great ice sheets, 18,000 years ago.
Last Glacial Maximum (LGM) The last time when the ice sheet reached its maximum extent, to the shelf break. In the Antarctic Peninsula, this occurred before 18,000 years ago.
Marine ice sheet An ice sheet, such as the West Antarctic Ice Sheet, where the bed is below sea level. The bed gets deeper inland for the West Antarctic Ice Sheet, which may make it unstable.
Mass balance Glaciers receive precipitation and melt. The zone where net accumulation exceeds net melting (ablation) is the accumulation zone. The zone where net melting exceeds net accumulation is the ablation zone. Mass balance is the balance between accumulation and ablation; if accumulation is greater, the glacier has a positive mass balance. If ablation is greater, then the glacier has a negative mass balance.
Mega scale glacial lineations (MSGLs) Elongate ridges in sediment produced under an ice sheet and typically under a fast-flowing ice stream, with lengths from 6-70 km and widths of 200-1300m. They can normally only be observed under remotely sensed images because of their large scale.
Mesa Flat topped mountain. On James Ross Island, the mesas are formed from flood basalts relating to subglacial volcanic eruptions.
Moraine Landform generated at the margins of a glacier by the movement of material to the glacier margin. Material may also be derived from debris transported on the glacier’s surface as well as from beneath the glacier.
Moulin A shaft melted by running water, where streams enter the glacier (into the englacial environment). They tend to be roughly circular, and can be very large.
Multibeam swath bathymetry See information at Woods Hole. Ship-based method of imaging the sea floor through sonar; the reflectance of ‘pings’ from a ship are analysed to measure the depth to the sea floor.
Nunatak Mountain that protrudes above the surface of an ice sheet.
Palaeoglaciology The study and reconstruction, using glacial geology and numerical computer models, of ancient glaciers and ice sheets.
Paraglacial A region, typically periglacial, where the ground water has been frozen for more than two years. The active layer, consisting of the uppermost sediments, seasonally thaws.
Periglacial A region with a cold climate, and processes and landforms associated with a cold climate. Typically occurs near glacierised regions.
Polythermal glacier A glacier that is wet-based in its centre but cold-based at its margins. This may result in thrusting at the ice margin, as the wet-based ice moves downslope under gravity and encounters the cold-based ice, which is frozen to its bed.
Sandur Wide braid plain in front of a glacier, formed by numerous meltwater streams exiting the glacier.
Subglacial Beneath the glacier. Includes basal sediments and the basal layers of ice.
Supraglacial On the surface of the glacier.
Thermal regime The temperature of the ice at the base of a glacier controls the subglacial environment. If it is warm enough, the ice will melt under the pressure of the ice above. This is the pressure melting point. Ice with water at the bed is warm-based. This ice lubricates the glacier sole and encourages deformation of subglacial sediments, sliding of the glaciers, and formation of tills and glacial landforms. If it is too cold, the ice will not melt, and the glacier will therefore be cold-based. These glaciers are frozen to the bed, exhibit little forward movement and generate few glacial sediments or landforms. Many small glaciers in particular may be polythermal, with warm-based ice in the thicker, upland parts of the glacier but cold-based ice at the thinner margins.
Tidewater glacier A glacier that originates on land but that flows out over the ocean, where it begins to float.
Till Sediment that is deposited at the glacier sole. Typically comprises fine-grained detritus, sand and gravel that was eroded, modified and transported by the glacier.
Tillite Glacial till that has been fully lithified (made hard like rock). In this case, the tillite originates from Neogene glaciation.
Tributary glacier A glacier that originates on land but flows out into the sea, where it begins to float. If the floating portion of the glacier combines with that of several other glaciers it forms a floating ice shelf.
Quaternary The last epoch of the Earth’s history; the last two-million years. During this epoch, glaciers and ice sheets came to dominate the Earth’s climate, when large global ‘glacials’ were interspersed with warmer ‘interglacials’.

 

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