Geography terms in Extreme environments

The loss of mass from a glacier by melting, sublimation, evaporation and calving; the zone of ablation is the lower part of a glacier, where annual losses exceed gains.

The addition of mass to a glacier by snowfall, avalanches, wind-blown snow and refreezing meltwater; the zone of accumulation is the upper part of a glacier, where annual gains exceed losses.

The surface layer of soil above permafrost that thaws each summer and refreezes each winter, from a few centimetres to several metres thick.

A period from about 14,500 to about 5,000 years ago, often called the Green Sahara, when stronger monsoon rains turned much of the Sahara into grassland and savanna with lakes and rivers.

A fan-shaped deposit of sediment formed where a stream or flash flood leaves a narrow valley or mountain front and spreads out onto a plain; merged fans form a bajada.

An illness caused by the low oxygen pressure at high altitude, with headache, nausea, fatigue and breathlessness, usually affecting people who climb quickly above about 2,500 m.

The international agreement, signed in 1959, that reserves Antarctica for peace and science, sets aside territorial claims and, through its 1991 Environmental Protocol, bans mineral extraction.

A narrow, steep-sided rock ridge formed where two cirques or glacial troughs erode back towards each other.

An environment in which potential evaporation greatly exceeds precipitation, giving a water deficit for most or all of the year; its aridity index lies between 0.05 and 0.2.

A soil of arid regions that is dry for most of the year, with little organic matter and often layers of calcium carbonate, gypsum or salts near the surface.

A permanent shortage of moisture in a climate, caused by low precipitation relative to potential evaporation; a long-term characteristic of a place, unlike drought, which is temporary.

A measure of dryness equal to mean annual precipitation divided by mean annual potential evapotranspiration; below 0.05 is hyper-arid, 0.05–0.2 arid, 0.2–0.5 semi-arid and 0.5–0.65 dry sub-humid.

Small-scale mining by individuals, families or small groups using simple tools, often informal or illegal, with little protection for workers or the environment.

A crescent-shaped dune with its horns pointing downwind and its slip face on the concave side, formed where sand is limited and the wind blows from one direction.

The movement of a glacier over its bed on a film of meltwater, possible only where the base is at the pressure melting point.

A cycle in which a place grows rapidly while a resource is profitable to extract and declines sharply when prices fall or the resource runs out.

Water with a much higher concentration of dissolved salts than seawater, produced as waste by desalination plants or found naturally beneath salt flats.

A method of obtaining lithium and other dissolved salts by pumping mineral-rich groundwater from beneath a salt flat into shallow ponds, where evaporation concentrates it before processing.

An isolated, steep-sided hill with a small flat top, higher than it is wide, formed as a mesa is worn back by weathering and erosion.

An irrigation system in which a line of sprinklers mounted on wheeled towers rotates around a central water supply, watering a circular field.

The idea, proposed by Jule Charney in 1975, that vegetation loss in drylands raises surface albedo and reduces rainfall, so that less vegetation grows: a positive feedback.

The decomposition of rock by chemical reactions that change its minerals, such as hydration, oxidation and solution; it needs water and is fastest in warm, wet climates.

An armchair-shaped hollow on a mountainside with a steep backwall, an over-deepened rock basin and a lip, eroded by a small glacier; it often holds a tarn after the ice melts.

The planned, permanent movement of a community away from a place made unsafe or uninhabitable by the effects of climate change, such as erosion or permafrost thaw.

A measure of relative variability equal to the standard deviation of a set of values divided by their mean, multiplied by 100; for annual rainfall, a higher percentage means less reliable rain.

A glacier whose base is below the pressure melting point and frozen to the bedrock, so it moves only slowly by internal deformation and does little erosion.

A technology in which mirrors focus sunlight onto a receiver to heat a fluid that drives a turbine; the heat can be stored, for example in molten salt, to generate power after dark.

The effect of distance from the sea on climate: places deep inside a large continent have a larger annual temperature range and usually less precipitation than coastal places at the same latitude.

Permafrost that underlies 90–100% of the ground surface, found where mean annual temperatures are well below freezing; it is often hundreds of metres thick.

Rights to own or use land that come from the traditions of a community, such as a village, clan or herding group, rather than from a title registered by the state.

The removal of loose, fine particles from the ground surface by wind, which lowers the land and can form deflation hollows.

A surface layer of closely packed pebbles and stones left when deflation removes the finer particles, which then protects the ground from further wind erosion.

Land degradation in arid, semi-arid and dry sub-humid areas resulting from various factors, including climatic variations and human activities (UNCCD definition).

Permafrost that underlies 50–90% of the ground, broken by unfrozen areas beneath lakes, rivers and warmer slopes.

The difference between the highest and lowest temperatures at a place within 24 hours, or between the mean daily maximum and mean daily minimum for a month.

Growing crops without irrigation in areas of low rainfall by conserving soil moisture, for example through fallowing, mulching and drought-tolerant crop varieties.

Areas with an aridity index below 0.65, made up of hyper-arid, arid, semi-arid and dry sub-humid lands, in which water is the main limit on plant growth and human activity.

The line on a glacier, often given as an altitude, at which annual accumulation equals annual ablation, separating the zone of accumulation from the zone of ablation.

A rock fragment, often a large boulder, transported by ice and deposited far from its source on bedrock of a different type, showing the direction and extent of former ice.

An environment in which climate and relief set severe limits on plant growth, human comfort and economic activity, so that it supports few people without special adaptation; cold, high-altitude and hot arid environments are the main types.

A low-cost method of restoring degraded farmland in which farmers protect and prune shoots growing from the living stumps and roots of trees and shrubs so they grow into trees.

The application of dissolved fertiliser through an irrigation system, usually drip irrigation, so that nutrients reach plant roots in the amounts and at the times the crop needs them.

Granular, compacted snow that has survived at least one summer melt season and is turning into glacier ice as burial squeezes out its air.

A way of employing workers at remote mines in which they are flown to the site for a shift of one to several weeks, living in camps, then flown home for a rest period.

Collecting water from fog by placing large vertical mesh nets in its path, so that droplets gather on the mesh and drip into a trough below.

The principle that Indigenous peoples may give or withhold consent to a project affecting their lands or resources, freely, before it begins and with full information about its impacts.

The breakdown of rock by repeated freezing and thawing of water in cracks and pores, which expands by about 9% when it freezes and pries the rock apart.

The upward swelling of the ground during freezing, caused by ice lenses growing in fine soil as water is drawn to the freezing front; it lifts stones towards the surface.

A sudden release of water from a lake dammed by a glacier or moraine when the dam is overtopped or breached, often after an ice or rock avalanche falls into the lake.

A long cold phase within an ice age, lasting tens of thousands of years, during which global temperatures fall, ice sheets and glaciers advance over large areas and sea level falls.

A glacier viewed as an open system, with inputs of snowfall, avalanches and wind-blown snow, stores of snow, firn and ice, transfers by ice flow, and outputs by melting, sublimation and calving.

A deep, straight valley with steep sides and a wide, flat floor, formed when a glacier deepens, widens and straightens a former river valley.

A large mass of ice, formed on land from compacted and recrystallised snow, that moves slowly downslope or outwards under its own weight.

The difference between a glacier's accumulation and ablation over a year, usually in metres of water equivalent; a positive balance leads to advance, a negative balance to thinning and retreat.

An African Union initiative adopted in 2007 to restore degraded land across the Sahel from Senegal to Djibouti, aiming to restore 100 million hectares by 2030.

A large atmospheric circulation in which air rises near the Equator, flows poleward at 12–15 km, sinks near 30° latitude, creating subtropical high pressure, and returns towards the Equator as the trade winds.

A tributary valley whose floor lies high above the floor of a main glacial trough, because its smaller glacier eroded less deeply; its stream enters the trough by a waterfall.

The strain on the body when it cannot lose enough heat to keep its core temperature stable, caused by high temperature, humidity, sunshine and exertion; it ranges from heat exhaustion to heat stroke.

A mountain or plateau environment outside the polar regions where low temperature, low air pressure, intense solar radiation and steep relief make conditions extreme because of height above sea level.

An arid environment with very low annual precipitation, usually under 250 mm, high daytime temperatures for most of the year and sparse vegetation, such as the Sahara or the Kalahari.

A dangerous fall in the body's core temperature below 35 °C, caused by losing heat faster than it is produced, especially in cold, wet or windy conditions.

A dome-shaped mass of glacier ice covering less than 50,000 km², usually over an upland or plateau, from which ice flows outwards in all directions.

A seasonal road built across frozen lakes, rivers, sea ice or tundra in winter, usable only while the ice is thick enough to carry vehicles.

A mass of glacier ice covering more than 50,000 km² of land, burying almost the whole land surface; the two present-day ice sheets cover Antarctica and Greenland.

An artificial glacier made in winter by piping and spraying stream water into cold air so that it freezes into a tall cone of ice, which melts slowly to supply water in spring.

A contract between a resource company and an Indigenous community setting out the jobs, training, payments and monitoring the community receives in return for supporting a project.

The physical difficulty of reaching a place because of barriers such as mountains, ice, sea ice, sand seas or a lack of roads, ports and airstrips, which may vary with the season.

The understanding, skills and practices developed by a local or indigenous community over many generations through close interaction with its environment, and passed on through culture and practice.

The descendants of the people who lived in a region before later settlers or states arrived, who keep distinct languages, cultures and ties to their land, such as the Inuit, Sámi or Tuareg.

The inability of a soil to support healthy plant growth because it lacks nutrients, organic matter or a suitable structure, or contains harmful levels of salt or other toxins.

A warmer phase between glacial periods, lasting thousands to tens of thousands of years, when ice sheets retreat to roughly their present extent; the present interglacial is the Holocene.

The slow flow of glacier ice as individual ice crystals deform and slide past one another under the pressure of the ice above.

An organisation of tour companies, founded in 1991, that sets and enforces rules for safe and environmentally responsible private travel to Antarctica among its members.

A wind of cold, dense air that flows downslope under gravity from an ice sheet, plateau or mountain, often reaching very high speeds where it is channelled into coastal valleys.

A long-term decline in the biological or economic productivity of land, caused by processes such as soil erosion, nutrient loss, salinisation and loss of vegetation.

The system of rules, set in law or by custom, that decides how land is owned, used, inherited and transferred, and by whom.

The rate at which air temperature falls with increasing height in the lower atmosphere; the environmental lapse rate averages about 6.5 °C per 1,000 m but varies with time and place.

The purchase or long-term lease of large areas of land, typically thousands of hectares, by companies, investment funds or foreign governments, often for export farming; called a land grab by critics.

The time, between about 26,000 and 20,000 years ago, when the ice sheets of the most recent glacial period reached their greatest extent and sea level was about 125 m lower than today.

A ridge of till along the side of a glacier or glacial valley, formed mainly from rock that fell from the valley sides.

A cool period from about 1300 (or the 16th century) to about 1850, during which glaciers in the Alps and elsewhere advanced to their largest extent of recent millennia.

A fine, yellowish, unstratified silt deposited by wind, often far from the desert or glacial outwash from which it was blown; it forms fertile but easily eroded soils.

A band of debris running along the middle of a glacier, formed where the lateral moraines of two joining glaciers merge.

An isolated, flat-topped hill with steep sides, wider than it is high, left where a resistant caprock protects weaker horizontal rocks as the surrounding plateau is eroded.

An armed group that is not part of a state’s regular armed forces, such as a rebel or paramilitary force, which may control territory and resources by force.

The removal of valuable solid minerals such as metal ores and diamonds, or of oil and natural gas, from the ground or the seabed by mining or drilling.

A ridge or mound of till carried and deposited by a glacier, named by its position as lateral, medial, terminal or recessional.

The transfer of a privately owned company or industry into ownership by the state, with or without compensation to its previous owners.

A way of life in which herders move their livestock between seasonal pastures and water sources instead of farming fixed fields, using mobility to cope with variable rainfall.

A satellite-derived measure of the greenness and density of vegetation, calculated from reflected red and near-infrared light, ranging from −1 to +1, with higher values meaning more vegetation.

A fertile area in a desert where groundwater reaches or comes close to the surface, through springs, wells or channels, allowing permanent settlement and irrigated farming.

A method of surface mining in which ore is removed from a large, stepped excavation open to the sky after the overlying rock and soil have been stripped away.

Sorted, rounded and often layered sand and gravel deposited by meltwater streams beyond or beneath a glacier.

Farming land so intensively, for example by shortening or abandoning fallow periods, that the soil loses nutrients, organic matter and structure faster than they are replaced.

Keeping more livestock on an area of pasture than its vegetation can support, so plants are eaten faster than they regrow and the soil is left bare and compacted.

A regular pattern of stone circles, polygons, nets or stripes on the ground in periglacial areas, produced mainly by frost heave, sorting of stones and, on slopes, solifluction.

A cold, non-glacial environment near ice sheets or glaciers or at high altitude, in which the ground is frozen for much or all of the year and repeated freezing and thawing shapes the land.

The warming and melting of ground ice in permafrost, which deepens the active layer, causes subsidence and releases stored carbon as carbon dioxide and methane.

A technology that converts sunlight directly into electricity in semiconductor cells, usually made of silicon, mounted in panels.

The breakdown of rock into smaller fragments without any change in its chemical composition, by processes such as thermal fracture, salt crystallisation and freeze-thaw.

A dome-shaped hill with a core of ice, up to about 70 m high, formed in permafrost areas when water under pressure freezes near the surface, in drained lake beds (closed system) or from rising groundwater (open system).

Glacial erosion in which meltwater freezes onto jointed bedrock, so that moving ice pulls away blocks of rock.

An environment in the high latitudes, mostly within the Arctic and Antarctic Circles, where the warmest month averages below about 10 °C, winters are long and dark, and precipitation is usually low.

A steep, pointed mountain summit with three or more faces, formed where three or more cirques have eroded back into the same peak, leaving arêtes between them.

A gently sloping underground tunnel that carries groundwater by gravity from an aquifer in higher ground to the surface at a lower point, with vertical shafts for construction and maintenance.

The most recent geological period, from about 2.58 million years ago to the present, characterised by repeated cycles of glacial and interglacial periods.

The reduction of precipitation on the leeward side of a mountain range, because moist air loses its water as it rises over the windward side and then descends, warms and dries.

The degree to which annual rainfall at a place differs from its long-term average from year to year; high variability means low reliability and is usually greatest where rainfall is lowest.

The distance, in space, time or cost, between a place and the main centres of population, markets, services and political power, which raises transport and labour costs and isolates residents.

The assertion by a state of greater control over the natural resources in its territory, through state companies, ownership limits, taxes, royalties or bans, so that more of the benefit stays in the country.

A desalination method in which seawater or brackish water is pumped at high pressure through a semi-permeable membrane that lets water pass but holds back dissolved salts.

A long, narrow lake that fills an over-deepened rock basin on the floor of a glacial trough.

An isolated rock with a narrow, undercut base and a wider cap, formed mainly by wind abrasion concentrated near the ground, helped by weathering at the base.

A payment made by a mining company to the owner of the mineral rights, usually the state, for each unit of resource extracted or as a share of its value or profit.

The physical weathering of rock by the growth and expansion of salt crystals in pores and cracks as salty water evaporates, which forces grains apart.

Frozen seawater floating on the ocean surface; in the Arctic it grows each winter and shrinks each summer to a minimum in September.

The process by which nomadic or semi-nomadic people settle permanently in one place, often encouraged by governments through boreholes, services or restrictions on movement.

A long, narrow, sharp-crested dune lying parallel to the average of two seasonal wind directions, which can stretch for tens to hundreds of kilometres.

A dry environment, usually on desert margins, with an aridity index of 0.2–0.5 and typically 250–500 mm of rain in a short wet season, supporting grassland, scrub and rain-fed farming in good years.

The steep leeward side of a sand dune, standing at about 32–34°, down which sand avalanches after being blown over the crest.

Electricity or heat generated from the energy of sunlight, either by photovoltaic panels or by concentrating sunlight to heat a fluid.

The slow downslope flow of saturated soil, especially of the thawed active layer over impermeable permafrost, forming lobes and terraces.

A large pyramidal dune with three or more radiating arms, each with a slip face, formed by winds from several directions; it grows upwards and moves little.

A zone of unfrozen ground within or beneath permafrost, usually under a lake or river; it may be closed, open or through.

A ridge of till that forms across a valley at the furthest point reached by a glacier's snout, marking its maximum advance.

The physical weathering of rock by repeated heating and cooling, which makes the outer layers expand and contract more than the interior, so they crack and peel away.

An irregular landscape of hollows, mounds and thaw lakes formed when ice-rich permafrost thaws and the ground subsides.

A sealed pipe containing a fluid that passively removes heat from the ground in winter, evaporating at its lower end and condensing at its finned upper end; used to keep permafrost frozen.

Unsorted sediment of clay, sand, gravel and angular boulders deposited directly by glacier ice.

A treeless biome of high latitudes and high mountains in which low temperatures and a short growing season limit vegetation to mosses, lichens, grasses and dwarf shrubs, usually over permafrost.

A non-binding declaration adopted by the UN General Assembly in 2007 that sets out the rights of Indigenous peoples to their lands, resources, cultures and self-determination.

A steep-sided, flat-floored dry valley in a desert, cut mainly by flash floods, that carries water only briefly after heavy rain.

A glacier whose base is at the pressure melting point, so a film of meltwater lets it slide over its bed; it moves relatively fast and erodes strongly.

The lowest temperature to which air can be cooled by evaporating water into it; it combines heat and humidity and indicates how well the human body can cool itself by sweating.

The wearing away of rock surfaces by sand grains carried by the wind, concentrated within about a metre of the ground.

The cooling effect of wind on exposed skin, expressed as the lower air temperature that would cause the same rate of heat loss in calm conditions.

A small planting pit, typically 20–40 cm across, dug before the rains and filled with manure or compost, that collects water and nutrients around a crop on crusted, degraded land.