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Common geoscientific terms and their definitions.



accelerator mass spectrometry: commonly known as AMS; a method for measuring 14C, 10Be and other isotopes including those produced by cosmic rays [accelerator mass spectrometer]

accretion: the process of [1] adding sediment to a river, beach or offshore area; [2] adding terranes to a landmass; [3] forming planets

acidic: relating to fluids with pH less than 7 [acid]

acoustics: the study and measurement of sound waves

aggregate: crushed rock, gravel or sand used for concrete or road making

Alert Level: the GNS Alert Level is a measure of the current status of the volcano.

alga: a primitive plant without complex structures [algae]

alkali feldspar: a group of light-coloured rock-forming potassium–sodium–aluminium silicate minerals.

alkaline: relating to [1] fluids with pH greater than 7 [alkali]; [2] igneous rocks with high concentrations of the alkali metals lithium, potassium, sodium, rubidium, cesium and/or radium.

alluvial: deposited by rivers [alluvium]

Alpine Fault: the c. 500 kilometre long transform fault that forms the Pacific–Australian plate boundary along western South Island

ammonite: an extinct mollusc with a multi-chambered, coiled, single calcareous shell—a relative of living nautiloids

amphibole: a group of dark-coloured, rock-forming, calcium–iron–magnesium silicate minerals

andesite: a volcanic rock intermediate in composition between basalt and rhyolite, common in volcanic arcs [andesitic]

Antarctic Circumpolar Current: the world's largest and strongest ocean current, which moves eastwards around Antarctica and links with other major ocean currents'

Antarctic Intermediate Water: cold, low salinity water that forms in subantarctic regions before sinking to between 700 and 1200 m ocean depth and spreading northward towards the equator

Antarctic Polar Front: the oceanic boundary between less-saline Antarctic Surface Water (equatorwards) and more-saline Circumpolar Surface Water (polewards)'. The Polar Front lies near the centre of the Antarctic Circumpolar Current, between about 50° and 65° South

Antarctic–Australia Ridge: the part of the mid-ocean ridge system that separates the Australian and Antarctic plates. It begins south of New Zealand at the Macquarie Triple Junction and extends west into the Indian Ocean

anticline: a fold in rock layers, generally convex upwards, where the oldest rocks are in the core

aquifer: a porous rock unit containing water that can be extracted

aragonite: a calcium carbonate mineral with the same chemical composition as calcite, but with a different crystal form [CaCO3]

arc front: an array of volcanoes directly above the upper zone of partial melting in a subduction zone

archaeology: the study of human history and prehistory through the excavation of sites and the analysis of physical remains

argon-40/argon-39 dating: commonly known as Ar–Ar dating; a variation of potassium–argon dating, in which the concentration of stable 40Ar, created from radioactive 40K in a reactor, is compared with the concentration of stable 39Ar

asthenosphere: a weak layer of the mantle below the lithosphere, which deforms plastically when subjected to stress

atmosphere: the envelope of gases surrounding the Earth

Australian Plate: the tectonic plate that includes Australia, the North Island and western South Island. It is also known as the Indo-Australian Plate'

axial ranges: the continuous chain of mountains in eastern North Island including (south to north) the Rimutaka, Tararua, Ruahine, Kaimanawa–Kaweka, Huiarau, Ikawhenua and Raukumara ranges. In South Island, the axial mountain chain includes (from south to north) the mountains of Fiordland, the Southern Alps, Spenser Mountains and St Arnaud Range

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back arc: the region, generally of rifting and subsidence, behind a volcanic arc

ballistic projectiles: Ballistic projectiles are pieces of rock thrown from a volcanic vent in an eruption. These rocks fall rapidly to the ground so rarely reach more than about 3 kilometres radius from the vent. There are two main types, volcanic blocks (large angular solid rock fragments) and volcanic bombs (thrown out as molten rock and smoothed or streamlined during flight)

basalt: a dark-coloured, silica- and alkali-poor volcanic rock composed mainly of plagioclase and pyroxene—the most common type of volcanic rock and a major constituent of the oceanic crust [basaltic]

basaltic andesite: a volcanic rock intermediate in composition between basalt and andesite, common in volcanic arcs

basement rocks: crystalline, indurated or metamorphosed rocks that underlie the softer sedimentary or volcanic cover rocks, and which are generally older than c. 100 Ma in Zealandia

bathymetry: the variation in depth of a water body, such as an ocean or a lake. Bathymetry is usually shown using contour lines of equal depth, or isobaths [bathymetric]

bedding: layers of rock of varying thickness and character [bed; bedded]

belemnite: an extinct, squid-like mollusc with an internal bullet-shaped, calcareous shell

benthic: bottom dwelling—in marine or fresh water

bentonite: a clay formed largely by alteration of volcanic ash, which swells in volume when water is added to it—a sodium–calcium–aluminium–magnesium silicate

beryllium-10 dating: a method for determining the age of [1] sedimentary deposits and [2] exposed surfaces using the in situ build-up over time of cosmogenic 10Be

biodiversity: the variety of plant and animal life— usually the number of species—in a region

biogenic ooze: a fine-grained soft sediment, usually on the deep-ocean floor, consisting mainly of microorganisms

biological productivity: the production of nutrients in the ocean

biology: the study of living organisms [biological]

biostratigraphy: the use of fossils to establish the order of rock succession [biostratigraphic]

biota: the plant and animal life of a region

bivalve: a mollusc with a hinged calcareous double shell—for example, a clam

black smoker: a submarine hydrothermal vent that emits metal-rich fluids with grey-black particles of iron–manganese compounds

brachiopod: commonly known as a lamp-shell; a filter-feeding animal with a hinged double, asymmetrical, calcareous shell

breccia: a coarse-grained sedimentary rock with angular clasts

bryozoan: a colonial filter-feeder that forms a calcareous branched or encrusted skeleton [bryozoa]

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caesium-137 dating: a method for determining the age of sediment or soil using the occurrence of 137Cs generated in atmospheric nuclear tests

calcareous: comprising or containing significant amounts of calcium carbonate

calcite: a commonly occurring, colourless, white or light-coloured calcium carbonate mineral [CaCO3]

caldera: a large, basin-shaped depression formed by the collapse of a volcano during or after an explosive eruption

calibration: the assignment of numerical ages to (1) the boundaries of geological time intervals; (2) dates derived using relative chronological methods, such as radiocarbon [calibrate]

carbonate: a commonly-occurring ion consisting of one atom of carbon and three atoms of oxygen (CO3). Combined with other elements, it forms common minerals such as calcite (calcium carbonate), dolomite (calcium magnesium carbonate) or siderite (iron carbonate)

carbon dioxide: a gas composed of carbon and oxygen [CO2] and a key greenhouse gas; the dissolved form is bicarbonate [HCO3-]

carbon isotopes: there are three naturally-occurring isotopes of carbon (C), the stable isotopes 12C and 13C and the radioactive isotope 14C (radiocarbon)

carbon monoxide: a colourless and odourless gas composed of carbon and oxygen [CO]

cement: a substance that holds together particles such as sand grains, pebbles or shell fragments. Common cementing substances in rocks are calcite, silica (silicon dioxide) or limonite (iron oxide) [cementation]

Cenozoic Era: the time span that started 65 million years ago and continues to the present day

CFC dating: a method for determining the age of groundwater using the occurrence of industrially produced chlorofluorocarbons

chalk: a soft, light-coloured, fine-grained limestone

chemistry: the study of the elements, the compounds they form and the reactions they undergo [chemical]

chemosynthesis: the process by which microbes convert inorganic compounds to carbohydrates or sugars without sunlight

chert: a hard flinty rock composed mainly of siliceous microfossils

chloride: the dissolved form of chlorine, and a common constituent of geothermal fluids [Cl-]

chronology: an arrangement of events in the order of their occurrence [chronological; chronometer]

clast: a rock fragment or grain broken or eroded from a larger rock. Many sedimentary rocks are called clastic rocks, because they are accumulations of debris eroded from older rocks

clay: [1] groups of (i) layered silicate minerals including kaolinite, illite, halloysite and smectite, (ii) oxide minerals including gibbsite, goethite and haematite, and (iii) extremely small minerals allophane and ferrihydrite; [2] a very fine-grained product of the chemical or physical break-down of rock and deposits [claystone]

closure temperature: the temperature below which a mineral retains the daughter products from in situ radioactive decay

coal: compressed plant remains—peat, lignite, subbituminous, bituminous and anthracite (in order of increasing carbon, and decreasing water, contents)

coccolithophorid: a microscopic single-celled marine plant that secretes calcareous plates [coccolith]

concretion: a hard, often spherical deposit formed by precipitation of minerals from solution within fine-grained rocks

condensate: hydrocarbon gases that condense into a liquid as pressure and temperature are reduced

conglomerate: a coarse-grained sedimentary rock with rounded clasts

conodont: a tooth-like phosphatic microfossil

continental crust: the 20–50 kilometre thick crust that underlies the continents

continental drift: plate tectonic movement of continents about the globe

continental shelf: the gently sloping submerged margin of a continent between the shore and the uppermost continental slope

continental slope: the region between the continental shelf and the deep-ocean floor

convection: continuous transfer of heat by slow circular movement [convective]

convergence (tectonic): the coming together of plates, usually resulting in mountain building or subduction [converge; convergent]

core: [1] the innermost part of a planetary body; [2] a sample of rock or deposits obtained by drilling or coring

correlation: the process of relating rocks or sedimentary deposits of the same essential character or age [correlate]

Coromandel Volcanic Zone: the volcanic arc active from c. 18 to 2 Ma along the present-day Coromandel Peninsula [Coromandel Arc]

cosmogenic isotopes: isotopes produced by primary cosmic rays in the atmosphere or by secondary cosmic rays in minerals contained in exposed rock surfaces

COSPEC: COrrelation SPECtrometer, used to measure a particular gas species, in this case sulphur dioxide in the gases from erupting Ruapehu. High SO2 levels indicate actively degassing magma at shallow depths.

cover rocks: rocks formed on top of basement rocks since about 100 Ma in Zealandia

crust: the outermost shell of the Earth [crustal]

crustacean: an aquatic, crab-like animal with a hard external skeleton [crustacea]

crustal assimilation: the incorporation of rock material into a magma as it moves through the crust

crystal fractionation: the crystallisation and settling out of minerals from a magma, modifying the magma’s composition

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dacite: A type of volcanic rock intermediate between andesite and rhyolite. Mount Tauhara at Taupo and Mount Edgecumbe (Putuaki) near Kawerau are examples of dacite volcanoes.

debris avalanche: a rapidly moving mass of material, resulting from sudden collapse of rocks or deposits on steep slopes. Commonly occurs on volcanoes

deep ocean: the abyssal depths beyond the base of the continental slope [deep sea]

deformation: the process of folding, faulting, shearing, compressing or stretching of rocks or soft sediments due to tectonic stress, or as a result of gravitational movements (e.g. landslides)

diatom: a microscopic single-cell form of alga with a siliceous shell

dike: a narrow intrusion, usually of magma, that cuts across the natural bedding or layering of the host rock

dinoflagellate: a single-celled, mobile plant-like organism (alga) with a resistant-walled cyst

dinosaur: large extinct reptile from the Mesozoic Era

dip: the inclination of a planar feature such as a layer within a rock, or a fracture plane in a rock. Usually measured in degrees, where 0° is horizontal, 20° is gentle, 65° is steep and 90° is vertical [dipping; also see strike]

discharge: the volume of flow of a moving liquid or gas. Examples include a river, a spring, a gas blow from a hydrothermal vent or flow from an artificial channel or pipe. Commonly measured in litres per second or cubic metres per second

DNA: deoxyribonucleic acid—the ‘genetic code’ molecule found in living tissues

dolomite: a light-coloured mineral composed on calcium magnesium carbonate. Commonly occurs as a magnesium-rich variant of limestone

DSIR: New Zealand’s Department of Scientific and Industrial Research (1926–1992)

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earthquake: a sudden motion or trembling in the crust caused by the abrupt release of accumulated stress along a fault

earthquake magnitude: commonly denoted as M; the size of an earthquake based on the original Richter scale

earthquake wave: the energy radiated from an earthquake source in the form of P-, S- and other waves [seismic wave]

eruption plume: cloud of volcanic ash emitted from a volcanic vent or volcano.

East Pacific Rise: the part of the mid-ocean ridge system east of New Zealand that separates the Pacific and Antarctic plates

echinoderm: a spiny-skinned marine animal that has five-part radial symmetry—for example, starfish, seaurchin

ecology: the study of the relationships of living things to each other and to their environment [ecological; ecologist]

economic minerals: geological materials that can be utilised profitably, including oil, gas, coal, metallic and non-metallic minerals, and water

ecosystem: a community of interacting organisms and their physical and chemical environment

effusive flow: a quiet, non-explosive eruption [effusion; extrusion]

electrical conductivity measurement: a geophysical method based on the ease with which current can pass through the ground [electrical resistivity]

electron spin resonance (ESR) dating: a method for determining the age of sediment using the change in magnetism in crystal lattices resulting from electrons dislodged by natural radiation

epicentre: the point on the Earth’s surface directly above an earthquake source

estuary: a coastal embayment or river mouth where fresh and marine water mix [estuarine]

evolution: [1] a biological process relating to change in form over time, leading to the rise of new species; [2] a non-biological process relating to gradual change, often from a simple to a more complex form [evolutionary; evolve; evolving]

Exclusive Economic Zone: the 200 nautical mile-wide offshore area adjacent to a country’s coastline, in which it has exclusive economic rights

extension (tectonic): the pulling apart of sections of the crust at faults or plate boundaries [extend; extensional]

extinction: the dying out of an entire class, family, genus or species

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fall deposit: Mantling blanket of pyroclastic particles (ash, scoria, pumice, etc) erupted explosively and transported through the atmosphere before falling back to the ground

fault: a major fracture or dislocation along which the crust has moved

fauna: the animal life of a region or geological interval

feldspar: a group of light-coloured potassium–sodium– calcium–aluminium silicate minerals—the most common mineral type in crustal rocks

ferromanganese deposit: an iron–manganese-rich nodule or crust formed in the deep ocean

fiord: a glacier-cut valley that has been flooded by the sea

flood plain: low- and flat-lying areas adjacent to a river, containing river-transported sediment deposited during floods

flora: the plant life of a region or geological interval

fold: a curve or bend in a planar geological structure such as bedding—varieties include anticline, syncline

food web: a complex set of feeding interactions and energy flows between species in an ecosystem

foraminiferan: a single-celled micro-organism with a calcareous shell [foraminifera]

forensics: scientific tests or techniques used in the investigation of crimes

formation: a body of rock unified by origin, age or composition

fossil: the remains, trace, or imprint of an ancient organism

fracture: a brittle crack in the crust

frequency of occurrence: the long-term average return period for earthquakes, volcanic eruptions, tsunamis, floods etc.

fumarole: an active volcanic vent that emits steam and other gases

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gamma radiation: naturally-occurring radiation resulting from decay of radioactive elements in minerals

gas hydrate: an ice-like crystalline solid formed from a mixture of water and natural gas, usually methane

gastropod: a mollusc with a single, asymmetrical shell that is usually spiral-coiled—for example, a snail

gene pool is the complete genetic potential (all of the available alleles) within a species or population

genus: in Linnaean classification, the second-lowest level used to group organisms, and consisting of one or more related species—for example, Agathis, the genus to which kauri trees belong

geochemistry: the study of the chemistry of the crust and mantle [geochemical; geochemist]

geochronology: [1] in general usage, the study and measurement of geological time; [2] with respect to radiometric dating, the determination of the time that a mineral first crystallised [geochronological; geochronologist]

geodetics: the study and measurement of ground movement

Geographic Information System: commonly known as GIS; a computer-based information system that uses a set of procedures and tools to store, integrate, manipulate, query, model and display geographically referenced and associated data

geography (physical): the study of the Earth’s physical features, resources and climate

geological hazards: natural events that threaten human existence, including earthquakes, floods, meteorite strike, tsunamis and volcanic eruptions [natural hazards]

geological map: a map that contains primarily geological information [geological mapping]

geological structure: the general disposition, attitude, arrangement or relative positions of rock masses

geological time: the time from the formation of the Earth 4.6 billion years ago to the present

geological timescale: a chronological arrangement or sequence of geological events—key timescales include the Global Geochronological Scale; the Geomagnetic Polarity Time Scale; the New Zealand Geological Timescale

geology: the study of the composition, structure and origin of the solid Earth; sub-disciplines include geochrononology, engineering geology, mineralogy, petrology, paleontology and stratigraphy [geological; geologist]

geomagnetic polarity: the configuration of the north and south magnetic poles of the geomagnetic field

geomagnetic stripes: a set of parallel magnetic anomalies that increase in age away from a mid-ocean ridge

geomagnetism: the study and measurement of the Earth’s magnetic field—the geomagnetic field

geomorphology: the study of the physical features of the Earth’s surface [geomorphological; geomorphologist]

geophysics: the study of the physical properties of the Earth [geophysical; geophysicist]

geoscience: the study of geology, geochemistry, geophysics, geomorphology, soil science and some aspects of hydrology, meteorology and oceanography [geoscientific; geoscientist]

geothermal: relating to [1] natural heat within the crust; [2] heat from hot groundwater or steam used for power generation

geothermometer: specific chemical compositions in minerals or fluids that indicate the temperature, at equilibrium, of a system

glaciation: a phase of globally cooler climate, with growth or expansion of glaciers or ice sheets in high-altitude or high-latitude land areas, and lowering of sea level by up to 120 m due to the build-up of glacier ice on land. During the last 800,000 years, Earth's climate has experienced periods of glaciation (or glacials) alternating with interglaciations (inrterglacials), on an approximate 100,000 year cycle. About 18,000 years ago, the last glaciation ended, and the climate reached full interglacial conditions about 11,700 years ago

glacier: a slowly moving mass of ice, formed where more snow accumulates over winter than can melt in summer. Excess snow compacts into glacier ice and flows downhill to lower warmer altitudes or, in polar regions, to iceberg-calving margins (e.g. Ross Ice Shelf in Antarctica) or arid zones where ice evaporation (sublimation) exceeds the flow rate (e.g. Dry Valleys of Antarctica). Glacier types include mountain valley glaciers (for example; Franz Josef Glacier or Tasman Glacier in the South Island) or ice sheets such as exist today on parts of Iceland or in Antarctica

Global Positioning System: commonly known as GPS; a satellite-based system for accurately determining locations on the Earth’s surface

global warming: an increase in global average temperature resulting from natural processes or human activity

Gondwana: the ancient super-continent in the Southern Hemisphere from which Zealandia split 83 million years ago [also known as Gondwanaland]

gradual evolution: an evolutionary pattern where new species develop as a result of gradual continuous changes throughout their history.

granite: a coarse-grained, crystalline plutonic rock rich in silica, alumina and alkali metals [granitic; granitoid]

graptolite: a dendritic, colonial fossil with a protein-like skeleton

gravity measurement: a geophysical method based on measurement of the attractive force of the Earth, which varies with altitude, latitude and the density of local rock masses

gravity anomaly: the difference between measured gravity and the expected (modelled) gravity at a site

greenhouse gas: an atmospheric gas, such as carbon dioxide or methane, which traps heat and causes global warming

greywacke: an indurated medium-grained sedimentary rock composed mainly of quartz, feldspar and rock fragments; often used collectively to mean greywacke plus argillite, a major constituent of basement terranes

ground shaking: the ground motion caused by an earthquake

ground truthing: the use of field observations to verify data obtained by remote sensing and office-based interpretations

groundwater: subsurface water contained in pores and fissures in rock beneath soil, most of which is beneath the water table

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habitat: the natural home of an organism

half-life: the time for half of an amount of a radioactive isotope to decay

hazard map: a map showing areas of relative risk for a particular geological hazard

Hazard Zones: the GNS Hazard Zones are a series of zones set up around Mt Ruapehu to indicate areas prone to various hazards (lava bombs, etc).

Hikurangi subduction system: the subduction zone east of the North Island, where the Pacific Plate descends beneath the Australian Plate

hydrocarbons: the chemical components of oil, natural gas and coal

hydrogen isotopes: the isotopes of hydrogen, namely 1H (hydrogen), 2H (deuterium) and 3H (tritium)

hydrogen sulphide: a poisonous, strongly odorous gas composed of hydrogen and sulphur [H2S]

hydrology: the study of land-based water systems, including rivers, lakes and groundwater

hydrophone: an instrument for detecting sound and seismic waves underwater

hydrothermal: relating to naturally occurring hot water—often referred to as ‘thermal’ at tourist locations—whose minimum temperature is higher than the ambient mean annual temperature

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ice age: an extended interval of cold glaciations and warmer interglacials, the most recent of which began c. 2.6 million years ago

ice core: a core of ice drilled from a glacier or ice sheet

ice sheet: a vast extent of ice covering a landmass [ice cap]

igneous: relating to rocks or minerals solidified from magma

ignimbrite: a volcanic deposit formed by a pyroclastic flow. Ignimbrite layers can be soft and full of pumice such as the land surface around Taupo (from the Taupo eruption 1800 years ago); or hard rock where the deposit has been thick and hot enough for the particles to fuse together (eg at Bulli and Te Toki Points on Lake Taupo).

impermeability: the inability of rocks or sediments to transmit fluid [impermeable]

interglaciation: a warm period between glaciations— the most recent (present) interglaciation is called the Holocene

intrusion: an igneous rock body that cooled and crystallised deep in the crust [intrude; intrusive]

invertebrate: an animal without a backbone

ionise: to give atoms an electrostatic charge [1] in a chemical reaction; [2] in a mass spectrometer [ion; ion source]

ironsand: black sands containing heavy minerals rich in iron—for example, magnetite, titanomagnetite and ilmenite

isotopes: forms of an element with differing numbers of neutrons [isotopic]

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ka: thousands of years ago (a point in time)

Kermadec Arc: the chain of largely submarine volcanoes northeast of New Zealand, including the Kermadec Islands

K/T boundary: the Cretaceous–Paleogene boundary (derived from ‘Cretaceous–Tertiary’), marked by a mass extinction of dinosaurs and other species

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lahar: a water-charged flow of volcanic debris

landslide: the down-slope movement of rock and soil under the influence of gravity

lapilli: material from 4 to 32mm in diameter blown out by a volcano.

Last Glacial Maximum: commonly known as the LGM the time of maximum global ice volume and minimum temperature between c. 24,000 and 18,000 years ago (extended by some scientists to 28,000–18,000 years ago in New Zealand)

Last (Otiran) Glaciation: : the most recent glaciation encompasses Stages 2 to 4 inclusive of the Marine Oxygen Isotope Scale (MIS), beginning at c. 71,000 years ago and ending at the start of the Holocene epoch at 11,700 years ago. In New Zealand, this glacial phase is known as the Otira Glaciation [last glacial; Otiran]

lava: molten rock that has reached the Earth's surface and been thrown out of or has flowed from a volcano or volcanic vent. Molten rock that is still underground is called magma

lava bombs: Blocks of lava greater than 32 mm in diameter thrown out of the volcano by an eruption.

lava dome: a hill produced by upward pressure of slowly oozing magma

lead isotopes: isotopes of lead, expressed as ratios of 206Pb, 207Pb or 208Pb and 204Pb, and used to determine the source and evolutionary history of rocks

lead-210 dating: a method for determining the age of sediment using the radioactive decay of the short-lived isotope 210Pb to stable 206Pb

limestone: a sedimentary rock composed of more than 50 percent calcium carbonate

lithification: to turn become a rock by chemical or physical means [lithify]

lithological: related to the physical character of a rock [lithology]

lithosphere: the outer shell of the Earth, consisting of the crust and upper mantle [lithospheric]

luminescence dating: a method for determining the age of sediment by measuring the amount of radiation it has received from its surroundings

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Ma: millions of years ago (a point in time)

macrofossil : a fossil typically more than one millimetre across that is easily visible to the naked eye

magma: molten or partly molten rock [magmatic; magmatism]

magma chamber: A large body of magma below the volcano that rises up through the column and feeds the volcano.

magma column: Pipe of magma within the volcano joining the magma chamber to the surface.

magnetism: the magnetic property of rocks or minerals

mantle: the part of the Earth’s interior between the core and the crust, composed of peridotite

mantle hot spot: a site of high heat flow from the mantle, usually associated with intra-plate volcanic activity

mantle wedge: the wedge-shaped region of mantle that lies between the subducting plate and over-riding plate

marine regression: retreat of the sea from the land marking a fall in relative sea level

marine transgression: an advance of the sea across the land marking a rise in relative sea level

Marlborough fault system: the system of faults in northern South Island between the Alpine Fault and the North Island fault system

mass extinction: a globally-significant event where large numbers of unrelated species suddenly die out

mass spectrometry: a method for separating ions of different mass, used for radiometric dating and isotope ratio measurement [mass spectrometer]

Mesozoic Era: the time span between 250 and 65 million years

metallurgy: the study of the production, purification and properties of metals

metamorphism: the alteration of rocks by heat and/or pressure [metamorphic; metamorphosed]

methane: a hydrocarbon—a major constituent of natural gas, and a key greenhouse gas [CH4]

mica: a variably-coloured group of layered, sheet-like silicate minerals that include muscovite and biotite

microfossil: a fossil typically less than one millimetre across that can usually be studied only under a microscope

micro-organism: a microscopic life form [microbe]

mid-ocean ridge: a submarine ridge system associated with seafloor spreading, in which basalt rises to the surface from the mantle

Milankovitch cycle: a repeating cycle of climatic fluctuation due to changes in the Earth’s orbit and in the tilt and wobble of the Earth’s axis

mineral: [1] a constituent of a rock with a specific chemical composition, or range of compositions [mineralogy; mineralogist]; [2] in an economic sense, a profitable geological commodity [mineralised; mineralisation]

mitigation: the reduction of the social and economic effects of geological hazards

moa: a large extinct flightless bird known only from New Zealand

mollusc: an invertebrate, typically with a calcareous shell—for example, a paua, scallop or squid

moraine: rock debris transported by a glacier and deposited along the glacier sides and front

mudstone: a fine-grained sedimentary rock of mixed silt and clay-sized grains [mud]

multi-beam sonar: a method for the detailed mapping of the seafloor based on multiple reflection of sound waves

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nannofossil: a tiny calcareous fossil, best studied using an electron microscope

nautilus: a mollusc with a multi-chambered coiled, single calcareous shell with a simpler internal chamber than an ammonite [nautiloid]

neoteny: when youthful characteristics are retained by the adult organism due to arrested development.

nitrate: the oxidised form of nitrogen, a major polluter of groundwater [NO3-]

normal fault: a fault in which the upper, hanging wall moves down with respect to the lower, footwall

North Island fault system: the system of faults between Cook Strait and the Bay of Plenty, including the Wellington and Wairarapa faults

Northland Arc: a volcanic arc active between 23 and 15 million years ago on the Northland peninsula

nutrient: a substance that provides essential nourishment for the maintenance of life

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oceanic crust: the 5–10 kilometre-thick crust generated at mid-ocean ridges that underlies the oceans

oceanography: the multidisciplinary study of the oceans [oceanographic; oceanographer]

ore body: a metallic or non-metallic mineral deposit that can be mined at a profit

orogenic: relating to [1] mountain building; [2] ore formation in metamorphic or sedimentary terranes

orographic: relating to precipitation caused by airflow over mountain ranges or hilly terrain

ostracod: a tiny free-swimming, aquatic crustacean with a hinged, double calcareous shell

oxide: a compound of oxygen with another element

oxygen isotopes : the stable isotopes of oxygen, expressed as 16O/18O (δ 18O), used either as an indicator of the source of rock material, the temperature of seawater or cave water or, when compared to a calibrated paleo-seawater curve, the age of fossil remains

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Pacific Plate: the tectonic plate that includes much of the Pacific Ocean and eastern South Island

pakohe: the Māori word for an indurated (‘baked’) mudstone

paleoclimate: ancient climate as determined from the geological record [paleoclimatic]

paleomagnetism: past geomagnetic field information that is preserved in rocks [paleomagnetic]

paleontology: study of life in the geological past [paleontological; palaeontologist]

Paleozoic Era: the time span between 540 and 250 million years ago

palynology: the study of spores, pollen, dinoflagellates and other acid-resistant organic structures [palynological; palynologist]

peat: plant material decomposed in water and partly carbonised

permeability: the ability of rocks or sediments to transmit fluid through interconnected pores or fractures [permeable]

petroleum: crude oil and natural gas

petrology: the study of rocks [petrologist]

Phanerozoic eon: The major unit of geological time in which abundant life has existed. It began about 542 million years ago.

phosphate: a phosphorous-bearing compound present in bones and cement [PO43-]

photosynthesis: the process by which plants and some micro-organisms use sunlight to convert carbon dioxide and water to carbohydrates and oxygen.

phreatic eruption: A small steam-driven volcanic explosion. The driving force is the flashing of hot water to steam by magmatic heat, but fresh magma itself is not involved.

phreatomagmatic eruption: A volcanic eruption of fresh magma that mixes with water. Falling ash from these eruptions is usually wet and sticky and often accompanied by rain.

physics: the study of the properties and interaction of matter and energy [physical]

phytoplankton: planktic plants such as algae, diatoms and coccolithophorids that help regulate the concentration of carbon dioxide in the ocean and atmosphere

pillow lava: lava in the shape of pillows with glassy margins, which is formed when lava erupts effusively into water

plagioclase: a group of light-coloured, rock-forming, sodium–calcium silicate minerals of the feldspar family

planktic: relating to organisms that float or drift in marine or fresh water [plankton]

plate (tectonic): a rigid segment of the crust and upper mantle [lithosphere]

plume: [1] a body of convecting fluid travelling upward through the mantle or crust; [2] a dense cloud of black, mineral-laden ‘smoke’ expelled from hydrothermal vents on the seafloor; [3] a suspension of muddy sediment discharged onto the continental shelf by rivers; [4] a concentration of pyroclastic (tephra) particles, aerosols and gases from an erupting volcano

plutonic: related to magma that has solidified deep in the crust [pluton; plutonism]

polar: regions between the Arctic or Antarctic circles and the north and south poles, respectively

polarised light: light that vibrates in a single plane, producing diagnostic interference colours in microscope thin sections

pollen: a fine powdery substance dispersed from a flower’s anther—the microscopic male reproductive cell of plants

porosity: the state of having open pore spaces in rocks

potassium-40–argon-40 dating: commonly known as K–Ar dating; a method for determining the age of rocks and minerals using the radioactive decay of 40K to stable 40Ar

pounamu: commonly known as greenstone; the Māori word for the mineral nephrite jade

progenesis: an early onset of reproductive maturity. It is when the organism reaches maturity when it is in its juvenile state.

prospect: a mineral occurrence that requires further investigation to determine if it is economic to mine

pumice: a light, frothy, volcanic rock full of bubble holes (vesicles) and usually composed of glassy rhyolite'

punctuated evolution: an evolutionary pattern in which new taxa (types of plants or animals) appear relatively suddenly via major shifts in characteristics within very short time spans and then remain constant in those characters for a period of time. (Shown by the graph on the right)

Puysegur subduction system: the subduction system southwest of New Zealand where the Australian Plate descends beneath the Pacific Plate

P-wave: a primary (pressure) earthquake wave—the first to arrive at a seismograph station

pyroclastic: relating to an explosive eruption or explosively erupted fragmental material—literally, ‘fiery fragments’

pyroclastic fall: Volcanic material that has been erupted explosively into the air and has fallen back to earth (for example, volcanic ash).

pyroclastic flow: a hot, gas-charged, fast moving, ground-hugging flow produced by an explosive eruption, where particles are concentrated at the base

pyroclastic material: Volcanic material erupted in an explosive volcanic eruption (for example, ash, lapilli, ignimbrite, etc).

pyroclastic surge: a hot, gas-charged, fast moving, ground-hugging flow produced by an explosive eruption, where particles are in a dilute suspension throughout the flowing mass

pyroxene: a group of black, magnesium–iron–calcium– aluminium silicate minerals

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quartz: a commonly occurring, variably-coloured mineral composed of silicon dioxide (SiO2), also known as silica. A rock composed largely of quartz is called quartzite [quartzose, silicious]

quiescence: relating to seismical, tectonical or volcanical inactivity [quiescent]

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radioactive decay: the breakdown of some isotopes by splitting of the atomic nucleus and the emission of subatomic particles

radiocarbon (carbon-14) dating: commonly known as carbon dating; a method for determining the age of carbon-bearing materials less than c. 60,000 years old, using the concentration of 14C calibrated against atmospheric 14C

radiolarian: a siliceous single-celled marine microorganism [radiolaria]

radiometric dating: a method for determining the age of geological materials using radioactive isotopes

remote sensing: the acquisition of information by remote means using, for example, satellites or ships

reserve: a mineral resource that has been defined to a high level of confidence and is extractable at a profit

reservoir: a porous volume within a rock formation containing fluids

resource(s): [1] economic mineral reserves plus all other known mineral deposits that may eventually become available; [2] mineral and energy sources that may be of economical use to society

return period: the average time between hazardous events

reverse fault : a fault in which the upper, hanging wall moves up with respect to the lower, footwall

rhyolite: A type of highly viscous magma with high silica content, it is found as pumice, ignimbrite, lava or obsidian. Rhyolite is also the name given to the volcanic rock formed from rhyolitic lava.

rift: a large region within a plate that is being pulled apart (extended) horizontally [rifting; rifted]

risk: the likelihood of suffering adverse consequences from being exposed to a hazard

rubidium–strontium dating: commonly known as Rb–Sr dating, this method for determining the age of rocks uses the decay of long-lived radioactive isotope 87Rb to stable isotope 87Sr

rupture: displacement along a fault-line

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saline: relating to a fluid with moderate to high concentrations of salts [haline; salinity]

samarium-147–neodymium-143 dating: commonly known as Nd–Sm dating; a method for determining the age of rocks using the radioactive decay of the long-lived isotope 147Sm to stable 143Nd

sandstone: a medium-grained sedimentary rock with cemented grains more than 60 micrometres in size [sand; sandy]

satellite altimetry: the use of satellites to determine the height of the Earth’s land or ocean surface

satellite telemetry: the use of satellites to transmit data

scarp: a cliff or bank formed by upward movement along a fault trace

schist: a foliated, metamorphosed rock derived typically from sandstone or greywacke

science: studies conducted on objective principles involving systematic observation and experimentation

scoria: a frothy basaltic rock, full of small gas bubbles, produced during weak explosive eruptions. Typically a black or red colour, it is common in the Auckland Volcanic Field

scoria cone: a small volcanic hill formed mainly of scoria erupted from a central vent

seamount: a submarine mountain rising 1000 metres or more above the seafloor

seafloor: the submarine surface below the seawater column [ocean floor]

seafloor spreading: the concept that new oceanic crust is created at mid-ocean ridges, causing lateral movement of the crust

sea level: the average height of the ocean’s surface, usually expressed as ‘mean sea level’, which is the average mid-point between high tide and low tide at any location. Generally taken as an elevation of 0 m and the reference datum for the elevation of the land surface, global sea level is approximated across the whole planet (including areas far from the sea) by the ‘geoid’, a geodetic reference surface’

sea level (eustatic): this is the ‘global sea level’; a true change in sea level, such as a rise due to melting of land-based ice, or a fall due to an increased volume of land-based ice, is called a eustatic change

sea level (relative): a change in sea level at any particular location relative to the position of the shoreline or depth of the water. A fall in relative sea level may be due to uplift of the crust, build-up of sediment on the sea floor or a true eustatic change; a rise in relative sea level may result from subsidence of the crust, erosion of sea floor sediment or a eustatic change

seal: a natural layer of impermeable rock that prevents seepage of oil, natural gas, water or other fluids from an underground hydrocarbon reservoir

sediment drift: a sedimentary deposit near the base of the continental slope formed by boundary currents

sediment: a deposit composed of mineral or rock particles transported by water, ice, wind, or gravity [sedimentary; sedimentologist]

sedimentology: the study of sediment and sedimentary processes

sedimentary basin: an area where notable thicknesses of sediment have accumulated, commonly due to subsidence of the crust

seiche: ("saysh") rhythmic waves produced in an enclosed or partially enclosed body of water. Wind-generated seiches are common on large lakes and enclosed seas, taking the form of a slow rise and fall of water level over periods of many minutes. Earthquake-shaking can generate seiches in lakes, bays, harbours or even swimming pools. Volcanic explosions may also generate seiches

seismic: relating to earthquakes [seismicity]

seismicity: Seismic activity; earthquakes and other shaking (tremors).

seismic reflection: the use of seismic vibration waves to explore the subsurface distribution of rock types or faults. The reflection of waves off, or refraction along, underground layers or structures, reveals the depths and positions of changes in rock density or character. This geophysical investigation method can utilise vibrations of natural earthquakes, or more commonly used an artificial source of vibration, such as explosions or sound waves

seismic tomography: the use of earthquake (seismic) waves to produce images of the Earth’s interior

seismograph: an instrument for measuring earthquake (seismic) waves

seismology: the study of earthquakes [seismological; seismologist]

self-sufficiency (energy resources): the proportion of domestic production relative to usage

shear: to dislocate and grind within a fault zone [shearing; shear belt]

shield volcano: a large, broad volcano with a flattened dome shape made up typically of basaltic lava flows. Although much modified by erosion, the extinct volcanoes of Akaroa and Lyttelton on Banks Peninsula are examples

silica: the common name of silicon dioxide (SiO2). Typically, it is found as the mineral quartz. Where silica crystals are very fine grained (cryptocrytalline), they form minerals such as opal and the chalcedony group, including agate. Sinters around hydrothermal vents are rich in silica. Organisms such as diatoms and radiolarian have silica skeletons. Accumulations of their remains (biogenic silica) form deep sea-floor oozes and where compacted into rock are called chert, or diatomite if composed mainly of diatoms. In magma, silica content has a great influence on the viscosity of the molten rock; basalt is poor in silica and is very hot and flows freely, while rhyolite is rich in silica, is cooler and more viscous. Erupting rhyolite is more prone to violent explosions as gas struggles to escape from the sticky lava [siliceous, silicic]

silicate: minerals whose key building-block is the silicon tetrahedron (SiO4). The bulk of the rocks forming the Earth’s crust are composed of silicate minerals, such as feldspar, olivine, pyroxene, amphiboles and mica

silicon-32 dating: a method for determining the age of ice or sediment using the build-up over time of the cosmogenic isotope 32Si

slate: moderately metamorphosed mudstone, which breaks into thin, parallel-sided slabs. Where subjected to more intense metamorphism, mudstones are converted into fine-grained schist rock

slip-rate: the average net rate of movement of crust along a fault

soil: the zone of intense biological activity immediately beneath the land surface. Soils vary in thickness and properties depending on their age and the parent materials from which they are formed. A typical soil profile in New Zealand consists of an A horizon, composed of dark, organic rich material that is the locus of invertebrate animal activity (e.g. worms) and bacterial action, passing downwards to a transition zone of somewhat disturbed and weathered material (B-horizon) resting on the undisturbed parent rock or deposit (C-horizon). The soil zone supports rooted plants, and is essential to life through recycling of nutrients, carbon and oxygen

source: [1] also known as the focus; the initiation point of an earthquake rupture; [2] the origin of crustal fluids—meteoric, magmatic or connate, including groundwater; [3] the origin of hydrocarbons leading to the formation of oil and gas reservoirs; [4] the location of the original material making up a rock

species: a basic level of life-form in the Linnaean classification—a group of organisms capable of interbreeding and producing fertile offspring—for example, Agathis australis is the species name for kauri trees

spore: the microscopic reproductive cell of many plants, fungi and algae, designed for dispersal and survival

stable isotope: a non-radioactive isotope of an element

stasis: morphologic constancy of a species through a stratigraphically significant time interval.

strain: the proportional change in shape or size resulting from the application of stress

strata: layers of sedimentary rock visually separable from those above and below [stratum; stratification]

stratigraphy: the order and relative position of rock units or other geological deposits in sequence [stratigraphic]

stratovolcano: a large, typically andesitic, conical volcano formed of interlayered lava flows and pyroclastic deposits

stress: the force per unit area acting on any surface within a 3D object

strike: the direction of a horizontal line on a planar feature such as a layer within a rock, or a fracture plane in a rock. Usually measured as a compass bearing, in degrees. Strike in combination with dip defines the orientation, or ‘attitude’, of any planar geological feature [striking; also see dip]

strike-slip: displacement parallel to the strike of a fault

Strombolian eruption: Volcanic eruption characterised by small explosive eruptions due do the viscous (thick) nature of the lava.

strontium isotopes: isotopes of strontium, expressed as the ratio 87Sr/86Sr, used either as an indicator of the source and evolutionary history of rock material or, when compared with a calibrated paleo-seawater curve, the age of calcareous fossils

subduction: the process by which an oceanic plate moves down into the mantle at a convergent plate margin [subduct]

submergence: the process of sinking below sea level [submerge]

submersible: a mini-submarine, remotely-operated vehicle or automatically-operated underwater vehicle used in seafloor studies

subsidence: the process of sinking with respect to sea level [subside]

subterranean: beneath the Earth’s surface

subtropical: the regions bordering the tropics to the south or north

succession: the natural time-order of rocks or fossils

sulphur: a yellow non-metal often found in volcanic or geothermal areas [S]; compounds are sulphides [S6-] or sulphates [SO42-]

sulphur dioxide: a colourless, choking poisonous gas often associated with volcanic or geothermal areas [SO2]

S-wave: a shearing earthquake wave—the second to arrive at a seismograph station

syncline: a fold in rock layers, generally concave upwards, where the youngest rocks are in the core

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Taupo Volcanic Zone: the c. 100 kilometre wide by c. 350 kilometre long volcanic region of central North Island extending north from Ruapehu volcano to beyond White Island volcano; the ‘older TVZ’ was active from c. 2 Ma to 340 ka, and the ‘younger TVZ’ has been active since c. 340 ka

taxonomy: the theory and practice of describing and classifying biota, rocks, soil etc.

tectonic: relating to the formation of large-scale structural features [tectonism; plate tectonics]

tectonic earthquakes: Earthquakes occurring in the crust of the earth and caused by movement on fault lines.

tephra: A collective term for all unconsolidated volcanic material erupted explosively. Includes volcanic ash, pumice, scoria, volcanic bombs, some pyroclastic flows, etc.

terrestrial: [1] land-based; [2] Earth-based

terrigenous sediment: sediment derived from the land

Thermohaline Circulation: the global system of oceanic currents that is driven by density contrasts, due to changes in heat and salt

thin section: a thin slice of a rock or mineral that can be analysed under a petrological microscope

thrust: a gently inclined reverse fault, in which the upper, hanging wall moves up with respect to the lower, footwall

transform fault: a strike-slip fault that terminates abruptly at a major transverse feature such as a midocean ridge

trap: an underground natural feature that allows oil, natural gas, water or other fluids to accumulate. Examples include structural traps such as anticlinal domes containing an impermeable layer of rock that traps fluids or gas in an underlying permeable rock layer, or where an impermeable fault zone cuts across a porous rock layer, trapping its fluids or gases under the fault. Stratigraphic traps may occur where a lensoid layer of permeable rock is overlain and cut off by a more continuous younger layer of impermeable rock

trench: a long, deep depression of the ocean floor marking a subduction plate boundary

trigger: a phenomenon or process that gives rise to a geological event such as an earthquake (triggered by build-up of strain in the crust), landslide (e.g. triggered by a rainstorm or by an earthquake) or a volcanic eruption (triggered by rise of magma)

trilobite: an extinct marine arthropod common in the Paleozoic Era

tritium dating: a method for determining the age of groundwater using the concentration of tritium (3H) produced by cosmic rays, and in particular by atmospheric nuclear tests in the 1950s and 1960s

tsunami: waves generated by the sudden displacement of a water body, commonly by an earthquake offset (uplift or subsidence) of the sea bed. Landslides or icefalls into lakes or fiords also may generate tsunamis

tuff ring: A wide low ring of pyroclastic material, surrounding a volcanic vent.

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UNCLOS: the United Nations Convention on the Law of the Sea

unconformity: a break in time within a sequence of rock layers. An unconformity may represent a period when no deposition took place, or may represent an interval of erosion that stripped away some rock layers, before deposition recommenced. Where the rock layers were tilted by tectonic movements and truncated by erosion before younger rock layers were deposited, bedding in the older, truncated layers dips more steeply than those of the younger layers on top; Such a configuration is called an angular unconformity [unconformable]

uplift: the raising of rocks from their place of formation

uranium–lead dating: a method for determining the age of rocks using the radioactive decay of long-lived isotopes of uranium to stable lead [thorium–lead dating]

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vent: Opening through which a volcano erupts or volcanic material passes.

vertebrate: an organism with a backbone

vesicularity: containing pores created by gas bubbles in volcanic rocks [vesicle; vesicular]

viscosity: the state of being sticky and resistant to flow [viscous]

vog: Smog of volcanic origin, composed of volcanic ash and gases.

volcanic arc: a chain of volcanoes, tens to hundreds of kilometres long, overlying a subduction zone

volcanic ash: Material in the form of small fragments from 0.06 to 4mm in diameter, blown out by a volcano.

volcanic centre: a group of volcanoes including stratovolcanoes, calderas, cones, domes etc. that are separated from adjacent volcanic centres by some tens of kilometres

volcanic dome: Gas-poor lava forming a steep-sided hill, usually close to an eruptive vent. Examples include Motutaiko Island (Lake Taupo), Mokoia Island (Lake Rotorua), the domes that make up Mount Ngongotaha (Rotorua), etc.

volcanic earthquakes: Earthquakes (up to about Magnitude 5.5) that are caused by the movement of magma within the crust.

volcanic eruption: Material from deep within the earth/magma chamber finds its way to the surface.

volcanic field: an area containing many small, isolated, mainly basaltic volcanic features (scoria cones, craters etc.)

volcanic gas: Gases released from a volcano or vent that were previously dissolved in magma.

volcanic massive sulphide: deposits of metal sulphide minerals, commonly rich in copper-zinc-lead, formed in association with undersea volcanic hydrothermal vents. Ancient examples are found in some rock sequences and may provide minable ore deposits. Modern examples are seen in ‘black smoker’ hydrothermal vents on the sea floor in volcanically active areas

volcano: A hole in the ground through which magma is erupted. More generally refers to a mountain or caldera that may have several vents. Not all volcanoes are cone-shaped mountains. (eg Lake Taupo).

volcanology: the study of volcanoes [volcanic; volcanism; volcanological; volcanogenic; volcanologist]

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water table: the upper surface of a zone of watersaturated rock or sediment

weathering: the chemical or physical break-down of rocks on the Earth’s surface

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X, Y

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Zealandia: also known as the New Zealand continent; the mainly submergent continental mass that split from Gondwana at c. 83 Ma

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testa - edited and published

test b

test b