Geology & Earth Sciences Vocabulary: 100 Key English Terms
Most textbooks, scientific articles, earthquake reports and geological maps that earth science students use are written in English, and international field camps and conferences run in English too. These terms cover what a geology or earth science student meets in the first months: rocks and minerals, plate tectonics, earthquakes and volcanoes, landforms, soil, water, weather and climate, and the maps and field methods that tie them together.
100 terms
11 topics
58 core terms
200 example sentences
Read, understand, keep going
No account needed. Read the meaning, see where the term is used, then study the examples. Click any word in the lesson for help. You can also select a word and press Alt + Enter.
Earth's Structure
geology
noun
Meaning
The science that studies the solid Earth: what it is made of, how its rocks and landforms formed, and how it has changed over time.
Where you use it
Used for the subject, the university department and the rocks of a place: study geology, a geology degree, the geology of Cappadocia. A person who studies it is a geologist; the adjective is geological (UK) or often geologic (US).
Examples
She is a second-year geology student at Ankara University.
The local geology explains why the town has so many springs.
Usage note
The stress falls on the second syllable: ge-OL-o-gy. The same is true for geologist.
Common phrases
study geology · structural geology · the local geology · geology department · field geology
The thin, rocky outer layer of the Earth. It is about 5 to 10 km thick under the oceans and usually 30 to 50 km thick under the continents.
Where you use it
Geologists distinguish oceanic crust, which is thin, dense and mostly basaltic, from continental crust, which is thicker, lighter and older. The boundary between the crust and the mantle is called the Moho.
Examples
The crust is thickest beneath high mountain ranges.
Oceanic crust is rarely older than about 200 million years because it sinks back into the mantle at subduction zones.
The thick layer of hot, mostly solid rock between the crust and the core, reaching a depth of about 2,900 km. It flows very slowly over millions of years.
Where you use it
Divided into the upper and lower mantle. Students often think it is liquid, but it is solid rock that can deform and flow slowly; only small parts melt to form magma. Common phrases: mantle convection, mantle plume, mantle rocks.
Examples
The mantle makes up most of the Earth's volume.
Pieces of the upper mantle can be seen at the surface in some ophiolites.
Usage note
Do not confuse it with 'mantel', the shelf above a fireplace, which sounds exactly the same.
The central part of the Earth, made mainly of iron and nickel. The outer core is liquid and creates the magnetic field; the inner core is solid.
Where you use it
Usually used with outer and inner: the outer core, the inner core, the core-mantle boundary. Most of what we know comes from seismic waves; for example, S waves cannot pass through the liquid outer core.
Examples
Movements in the liquid outer core generate the Earth's magnetic field.
Seismologists first detected the inner core in the 1930s.
Usage note
In drilling, a core is a cylinder of rock cut from a borehole; Turkish geologists call it 'karot'. The context tells you which meaning is meant.
The rigid outer shell of the Earth, made of the crust and the uppermost part of the mantle. It is broken into tectonic plates and is typically around 100 km thick.
Where you use it
Used when explaining plate tectonics. Note the difference: crust and mantle are layers defined by composition, while lithosphere and asthenosphere are defined by strength. Common phrases: oceanic lithosphere, continental lithosphere.
Examples
Tectonic plates are pieces of the lithosphere.
Old oceanic lithosphere is cold and dense, so it sinks easily.
Common phrases
oceanic lithosphere · continental lithosphere · the base of the lithosphere · lithospheric plate
The hot, weak layer of the upper mantle just below the lithosphere, which can flow slowly and allows the tectonic plates above it to move.
Where you use it
Used in plate tectonics lectures together with lithosphere. It is mostly solid, but high temperature and a little melt make it soft and ductile. It lies roughly 100 to 350 km below the surface, although estimates of its depth vary.
Examples
The rigid plates slide over the weaker asthenosphere.
Seismic waves slow down when they enter the asthenosphere.
Common phrases
the lithosphere and asthenosphere · the upper asthenosphere · asthenospheric flow · low-velocity zone
A circular flow in a fluid or soft solid in which hot material rises, spreads, cools and sinks again. In the mantle, it carries heat towards the surface.
Where you use it
Used in school and university explanations of why plates move. Geologists now see mantle convection as only part of the story: the pull of sinking plates at subduction zones (slab pull) is considered a major driving force. Also used in meteorology.
Examples
Convection currents in the mantle carry heat from the core towards the surface.
Older textbooks say that convection currents push the plates, but the full picture is more complex.
Common phrases
mantle convection currents · convection cell · rising convection current · heat transfer
A natural solid material made mostly of minerals, such as granite or limestone. Rocks make up the Earth's crust and are grouped by how they formed.
Where you use it
The basic word of geology. It is uncountable for the material (hard rock, solid rock) and countable for rock types and pieces (volcanic rocks, a rock sample). Common verbs: form, expose, break, date, describe.
Examples
These rocks formed on the sea floor about 100 million years ago.
Label each rock sample with the date and the location.
Usage note
'Rock' is the natural material; 'stone' is used for building stone, gems and names such as limestone. A geologist says 'a rock sample', not 'a stone sample'.
Common phrases
rock type · rock sample · solid rock · volcanic rocks · rock formation
A naturally occurring, inorganic solid with a definite chemical composition and an ordered internal structure, such as quartz, calcite or feldspar.
Where you use it
Used in mineralogy labs, rock descriptions and mining. Students identify minerals by colour, hardness, cleavage and lustre. 'Mineral deposits' and 'mineral resources' are economic terms; 'rock-forming minerals' are the few common minerals that build most rocks.
Examples
Quartz and feldspar are the most common minerals in granite.
Use a hand lens to identify the main minerals in each sample.
Usage note
In everyday English 'minerals' can also mean nutrients in food, such as iron or calcium. In geology the word always means a natural crystalline solid.
Common phrases
identify a mineral · rock-forming minerals · mineral deposit · clay minerals · mineral composition
Rock that forms when molten magma or lava cools and becomes solid. Granite forms slowly underground, while basalt forms quickly at the surface.
Where you use it
One of the three main rock groups. Textbooks divide igneous rocks into intrusive (plutonic) rocks, which cool inside the crust, and extrusive (volcanic) rocks, which cool at the surface. Grain size usually tells you which is which.
Examples
The large crystals tell us that this igneous rock cooled slowly at depth.
Most of the oceanic crust is made of igneous rocks such as basalt and gabbro.
Usage note
Pronounced IG-nee-us. The word comes from Latin 'ignis', meaning fire.
Common phrases
intrusive igneous rock · extrusive igneous rock · igneous intrusion · igneous activity
Rock formed when sediment such as sand, mud or shells is laid down in layers, then buried, pressed together and cemented over time.
Where you use it
Covers sandstone, shale, limestone, conglomerate and salt deposits. Geologists study sedimentary rocks for fossils, past environments, groundwater, oil and gas. Typical features are bedding, ripple marks, cross-bedding and fossils.
Examples
Most fossils are found in sedimentary rocks.
The valley walls show a thick sequence of sedimentary rocks laid down in a shallow sea.
Rock that has been changed by heat, pressure or hot fluids deep in the Earth without melting, such as marble formed from limestone.
Where you use it
The third main rock group. Geologists name the original rock (the protolith) and the grade of metamorphism: as temperature and pressure rise, shale becomes slate, then schist and gneiss. A layered texture called foliation is typical.
Examples
Marble is a metamorphic rock that forms from limestone.
The Menderes Massif in western Turkey is known for its metamorphic rocks.
Common phrases
high-grade metamorphic rock · low-grade metamorphic rock · foliated metamorphic rock · metamorphic belt
The model that shows how igneous, sedimentary and metamorphic rocks change into one another over long periods through melting, weathering, burial and heat.
Where you use it
Taught in the first weeks of every geology course, usually as a diagram with arrows. Students explain the steps with verbs such as melt, cool, weather, erode, deposit, bury and metamorphose.
Examples
Draw the rock cycle and write a process on every arrow.
In the rock cycle, a granite can become sand, then sandstone, then quartzite.
Common phrases
the rock cycle diagram · stages of the rock cycle · part of the rock cycle
A solid in which the atoms are arranged in a regular, repeating pattern, which often gives it flat faces and a typical shape.
Where you use it
Used in mineralogy and petrology: crystals grow, form and can be well-formed or broken. In igneous rocks, crystal size shows how fast the magma cooled. Related words: crystalline (adjective) and crystallise or crystallize (verb).
Examples
Slow cooling allows large crystals to grow.
The quartz crystals in this vein are up to 5 cm long.
A light-coloured, coarse-grained igneous rock made mainly of quartz, feldspar and mica, formed when magma cools slowly deep in the crust.
Where you use it
The classic textbook example of an intrusive igneous rock. Large bodies of granite are called plutons or batholiths. In the stone trade, 'granite' is used loosely for many hard decorative stones that are not true granite.
Examples
Granite is common in continental crust but almost absent from the ocean floor.
You can see large pink feldspar crystals in this granite.
A dark, fine-grained igneous rock formed when lava cools quickly at or near the surface. It is the most common volcanic rock and makes up the ocean floor.
Where you use it
Used in volcanology, petrology and marine geology: basalt flows, basaltic lava, columnar basalt. Basalt is the volcanic equivalent of gabbro. In Turkey it is widespread in eastern and south-eastern Anatolia; the city walls of Diyarbakır are built of it.
Examples
The plateau is covered by thick basalt flows.
Columns in basalt form when a thick lava flow cools and contracts.
A sedimentary rock made mostly of calcium carbonate in the form of the mineral calcite, often built from the shells and skeletons of sea creatures.
Where you use it
Very common in Turkey, especially in the Taurus Mountains. In the field, geologists test it with a drop of dilute hydrochloric acid: limestone fizzes. It dissolves slowly in rainwater, forming caves and karst landscapes, and is used to make cement.
Examples
Put a drop of acid on it: if it fizzes, it is probably limestone.
The cave formed as groundwater slowly dissolved the limestone.
Usage note
Dolomite looks similar but fizzes only weakly, or only when powdered, so do not identify limestone by colour alone.
A mineral's resistance to being scratched, measured on the Mohs scale from 1 (talc) to 10 (diamond). It is one of the first tests used to identify minerals.
Where you use it
In the lab, students scratch minerals with a fingernail (about 2.5), a copper coin (about 3) and a steel knife or glass (about 5.5). Quartz, at 7, scratches glass. Phrases: hardness test, a hardness of 7, harder than glass.
Examples
Calcite has a hardness of 3, so a knife scratches it easily.
Check the hardness before you decide whether it is quartz or calcite.
Common phrases
Mohs hardness scale · hardness test · a hardness of 7 · relative hardness
The tendency of a mineral to break along flat, smooth planes of weakness in its crystal structure. Mica splits into thin sheets because of its perfect cleavage.
Where you use it
Described by quality (perfect, good, poor) and number of directions: one in mica, two in feldspar, three in calcite and halite. Minerals without cleavage, like quartz, show fracture instead. In metamorphic rocks, 'slaty cleavage' is a rock texture.
Examples
Feldspar has two cleavage planes at nearly right angles.
Calcite breaks into rhomb-shaped pieces because it has three directions of cleavage.
Usage note
In everyday English 'cleavage' also refers to the space between a woman's breasts, so be careful with the word outside a geology context.
Common phrases
perfect cleavage · cleavage plane · two directions of cleavage · slaty cleavage · cleavage and fracture
A hard, common mineral made of silicon dioxide (SiO2), usually clear, white or grey with a glassy lustre. It has a hardness of 7 and no cleavage.
Where you use it
One of the most important rock-forming minerals, found in granite, sandstone, quartzite and veins. It resists weathering, so most beach and desert sand is quartz. It breaks with a curved, shell-like (conchoidal) fracture.
Examples
The white veins cutting through the rock are quartz.
The remains or traces of a plant or animal that lived long ago, preserved in rock, such as shells, bones, leaf impressions or footprints.
Where you use it
Geologists find, collect, identify and date fossils, and use them to work out the age of rocks and past environments. Body fossils are actual remains; trace fossils are signs of activity such as burrows. Also used as an adjective: fossil fuel, fossil record.
Examples
This limestone is full of fossil shells.
The fossils in this layer show that the area was once under the sea.
Common phrases
fossil record · fossil shells · trace fossil · find a fossil · fossil fuel
A single layer of sedimentary rock or sediment with similar features throughout, separated from the layers above and below it. The plural is strata.
Where you use it
Much more common in the plural: rock strata, folded strata, younger strata. In the field, geologists often say 'bed' or 'layer' for a single layer. The study of strata is called stratigraphy.
Examples
The strata dip gently towards the south.
Each stratum in the cliff records a different period of deposition.
Usage note
'Strata' is plural. Say 'a stratum' and 'these strata are', never 'a strata'.
The system that divides the Earth's roughly 4.6-billion-year history into named units such as eons, eras, periods and epochs, based on rocks and fossils.
Where you use it
Called the geological time scale in the UK. The official chart is published by the International Commission on Stratigraphy. Students learn names such as Palaeozoic, Mesozoic, Cenozoic, Jurassic and Cretaceous, and place events on the scale.
Examples
On the geologic time scale, the Jurassic is a period within the Mesozoic era.
Learn the main units of the geologic time scale before the exam.
Usage note
English and Turkish names differ: Jurassic is 'Jura', Cretaceous is 'Kretase', Cenozoic is 'Senozoyik' and Palaeozoic (US Paleozoic) is 'Paleozoyik'.
Common phrases
the geologic time scale · units of the geologic time scale · on the geologic time scale
A method of finding the age of rocks and minerals by measuring how much of a radioactive element has decayed into its products, using the known rate of decay.
Where you use it
Gives numerical (absolute) ages in years, unlike relative dating. Common methods include uranium-lead for very old rocks, potassium-argon and argon-argon for volcanic rocks, and carbon-14 for organic material up to about 50,000 years old.
Examples
Radiometric dating shows that the oldest rocks in the region are about 500 million years old.
We sent the zircon crystals to the lab for radiometric dating.
Usage note
Carbon-14 cannot date dinosaur bones or most rocks: it only works for material up to about 50,000 years old.
Common phrases
radiometric dating methods · uranium-lead dating · radiocarbon dating · absolute age
The time it takes for half of the atoms of a radioactive isotope in a sample to decay. Each isotope has its own fixed half-life.
Where you use it
The basis of radiometric dating. Half-lives range from fractions of a second to billions of years: carbon-14 has a half-life of about 5,730 years and uranium-238 about 4.5 billion years. Usually written with a hyphen; the plural is half-lives.
Examples
After one half-life, half of the original isotope remains; after two, only a quarter is left.
Uranium-238 has a half-life of about 4.5 billion years.
Common phrases
a half-life of · a short half-life · a long half-life · radioactive half-life
The principle that in undisturbed layers of sedimentary rock, the oldest layer is at the bottom and each layer above it is younger.
Where you use it
One of the basic principles of relative dating, first described by Nicolas Steno in the 17th century. Geologists apply it with care, because folding and faulting can turn layers upside down. Also called the principle of superposition.
Examples
By the law of superposition, the sandstone at the base of the cliff is the oldest unit.
Fossils showed that the law of superposition could not be applied here, because the strata were overturned.
Common phrases
the law of superposition · apply the law of superposition · principle of superposition · relative dating
A surface between rock layers that marks a gap in the geological record, where erosion removed rock or no sediment was deposited for a long time.
Where you use it
Types include the angular unconformity (tilted layers below flat ones), the disconformity and the nonconformity (sediment on igneous or metamorphic rock). Siccar Point in Scotland, described by James Hutton, is a famous example.
Examples
The angular unconformity shows that the older rocks were folded and eroded before the sea returned.
About 50 million years of record are missing at this unconformity.
Common phrases
angular unconformity · unconformity surface · major unconformity · lie above an unconformity
A fossil of a species that lived for only a short time but was widespread and easy to identify, so it is used to date rock layers and match them between areas.
Where you use it
Used in biostratigraphy and correlation. Ammonites, trilobites and foraminifera are classic index fossils. In Turkey, nummulites are well-known index fossils of Eocene limestones. Also called a guide fossil or zone fossil.
Examples
This ammonite is an index fossil for the Early Jurassic.
Index fossils allowed us to correlate the two sections across the valley.
Common phrases
use index fossils · a good index fossil · biostratigraphy · fossil zone
The theory that the Earth's outer shell is broken into large plates that move slowly, causing earthquakes, volcanoes, mountain building and the movement of continents.
Where you use it
The central theory of modern geology, widely accepted since the 1960s. It takes a singular verb: 'plate tectonics explains...'. Used in lectures, textbooks and whenever someone explains why a region has earthquakes or volcanoes.
Examples
Plate tectonics explains why most earthquakes happen along narrow belts.
You cannot understand the geology of Anatolia without plate tectonics.
Usage note
Use a singular verb: 'plate tectonics is', not 'plate tectonics are'.
Common phrases
theory of plate tectonics · plate tectonics explains · modern plate tectonics
One of the large, rigid pieces of the Earth's lithosphere that move slowly over the mantle, usually by a few centimetres a year.
Where you use it
Often shortened to 'plate': the African Plate, the Eurasian Plate. Plates move apart, collide or slide past each other. Most of Turkey sits on the small Anatolian Plate, squeezed between the Eurasian, African and Arabian plates.
Examples
The Arabian tectonic plate is moving north towards Eurasia.
Tectonic plates move at about the speed your fingernails grow.
Common phrases
tectonic plate movement · the Eurasian Plate · plates collide · plate motion
A fracture in the Earth's crust along which the rocks on either side have moved. Sudden slip on a fault causes an earthquake.
Where you use it
Faults are named by their movement: normal, reverse, thrust and strike-slip faults. A fault zone is a wide band of faults, and a fault line is the trace of a fault at the surface. Faults slip, rupture or are reactivated.
Examples
The North Anatolian Fault is a right-lateral strike-slip fault.
We mapped the fault where it cuts across the road.
Usage note
Here 'fault' has nothing to do with blame. Do not confuse it with everyday 'it's my fault', meaning 'I am to blame'.
Common phrases
active fault · fault zone · strike-slip fault · normal fault · fault line
The zone where two tectonic plates meet. Plates move apart at divergent boundaries, towards each other at convergent boundaries and past each other at transform boundaries.
Where you use it
Most earthquakes and volcanoes occur near plate boundaries, so the term is common in hazard discussions. Typical adjectives: divergent, convergent, transform, active. Examples: the Mid-Atlantic Ridge (divergent) and the San Andreas Fault (transform).
Examples
Iceland sits on a divergent plate boundary.
The East Anatolian Fault forms part of the plate boundary between the Anatolian and Arabian plates.
Common phrases
divergent plate boundary · convergent plate boundary · transform plate boundary · along the plate boundary
The process in which one tectonic plate, usually an oceanic one, sinks beneath another plate and down into the mantle at a convergent boundary.
Where you use it
Most often seen in 'subduction zone', where deep ocean trenches, very large earthquakes and chains of volcanoes form, as in Japan and the Andes. The verb is subduct: 'the plate is being subducted'.
Examples
South of Crete, the African Plate sinks beneath the Aegean along the Hellenic subduction zone.
Subduction zones produce the largest earthquakes on Earth.
Common phrases
subduction zone · active subduction · slab subduction · subduction-related volcanism
A bend or curve in layers of rock, formed when the rocks are slowly squeezed by tectonic forces without breaking.
Where you use it
The basic types are anticlines, which arch upwards with the oldest rocks in the core, and synclines, which sag downwards with the youngest rocks in the core. Geologists measure the fold axis and limbs. Also a verb: folded strata, the rocks were folded.
Examples
The limestone layers in this cliff form a tight fold.
Oil often collects at the top of an anticline, a type of upward fold.
Common phrases
anticline and syncline · fold axis · tight fold · fold belt · folded strata
A long underwater mountain chain where two plates move apart and new oceanic crust forms from rising magma, such as the Mid-Atlantic Ridge.
Where you use it
Linked to seafloor spreading: the ocean floor gets older with distance from the ridge. Mid-ocean ridges form a connected system more than 60,000 km long around the globe. Common phrases: form at the ridge, ridge axis, spreading rate.
Examples
New oceanic crust is created at mid-ocean ridges.
Iceland is one of the few places where a mid-ocean ridge rises above sea level.
A long valley formed where the crust is stretched and pulled apart, so that a block of land drops down between faults. The East African Rift is a well-known example.
Where you use it
Used for divergent boundaries on land and the early stages of ocean opening; the Red Sea is a rift that the sea has flooded. Related terms: rifting, rift zone, graben. Western Anatolia's Gediz and Büyük Menderes grabens formed through similar crustal stretching.
Examples
The East African Rift Valley may one day split the continent in two.
Deep lakes often form on the floor of a rift valley.
Common phrases
the East African Rift Valley · rift zone · continental rifting · rift basin
The idea, proposed by Alfred Wegener in 1912, that the continents have slowly moved across the Earth's surface and were once joined in a supercontinent called Pangaea.
Where you use it
Wegener's evidence included the matching coastlines of Africa and South America, similar fossils and rocks on different continents, and clues to past climates. The idea was rejected for decades and was later explained by plate tectonics.
Examples
Matching fossils in Africa and South America support the idea of continental drift.
Wegener could not explain what caused continental drift.
Common phrases
theory of continental drift · evidence for continental drift · Wegener's continental drift
A sudden shaking of the ground caused by rocks breaking and slipping along a fault, which releases energy as seismic waves.
Where you use it
Common in news, reports and lectures: an earthquake strikes, hits a region, is felt in a city. Scientists say 'quake' informally, 'event' in technical reports and 'seismic activity' when talking about many earthquakes.
Examples
The earthquake was felt as far away as Istanbul.
Many large earthquakes in Turkey have occurred along the North Anatolian Fault.
Common phrases
a strong earthquake · an earthquake strikes · earthquake zone · earthquake-resistant building
A number that describes the size of an earthquake at its source, based on the energy released. Each whole step on the scale means about 32 times more energy.
Where you use it
Written 'a magnitude 6.8 earthquake' or 'M 6.8'. Seismologists today mostly use moment magnitude (Mw); the Richter scale is now mainly historical. People say an earthquake 'had a magnitude of' or 'measured' a value.
Examples
A magnitude 5.9 earthquake struck the region early this morning.
The two agencies reported slightly different magnitudes for the same event.
Usage note
English uses a decimal point (magnitude 6.8), Turkish a decimal comma (6,8). Do not translate 'şiddet' as magnitude: 'şiddet' is intensity.
Common phrases
moment magnitude · a magnitude 7 earthquake · a magnitude of · magnitude scale
The point on the Earth's surface directly above the place underground where an earthquake starts.
Where you use it
Usually given with distance and direction: 'the epicenter was 12 km south of the town'. The US spelling is epicenter, the UK spelling epicentre. It is also used figuratively, as in 'the epicentre of the crisis'.
Examples
The epicenter was offshore, about 20 km from the coast.
Damage was worst in the villages closest to the epicentre.
Common phrases
the epicenter of the earthquake · near the epicenter · the epicenter was located · epicentral area
A wave of energy that travels through the Earth or along its surface, produced by an earthquake, an explosion or another sudden ground movement.
Where you use it
Students learn three main types: P waves (fastest, compress the rock), S waves (shear the rock and cannot cross liquids) and surface waves (slowest and usually the most damaging). Seismic waves travel, arrive, are recorded and are reflected.
Examples
Seismic waves from the earthquake reached stations around the world within minutes.
Seismic waves slow down and grow larger when they pass through soft sediment.
Common phrases
P wave · S wave · surface waves · seismic wave velocity · travel time
A smaller earthquake that follows a larger one in the same area as the crust adjusts after the main shock. Aftershocks can continue for months or years.
Where you use it
Used in news and seismology reports: strong aftershocks, an aftershock sequence, aftershocks were felt. Related words: mainshock (the largest event) and foreshock (a smaller earthquake before it). Damaged buildings may collapse in a strong aftershock.
Examples
Hundreds of aftershocks were recorded in the first 24 hours.
Engineers warned people not to enter damaged buildings because of the risk of aftershocks.
Common phrases
a strong aftershock · aftershock sequence · a series of aftershocks · aftershock activity
The point underground where an earthquake rupture starts, also called the focus. Its depth below the surface is called the focal depth.
Where you use it
Given in seismology reports with its depth: 'a shallow hypocenter at 10 km'. Shallow earthquakes, less than about 70 km deep, usually cause more damage than deeper ones of the same magnitude. The UK spelling is hypocentre.
Examples
The hypocenter was only 8 km deep, which explains the heavy damage.
Seismologists locate the hypocentre using arrival times at many stations.
Common phrases
focal depth · a shallow hypocenter · locate the hypocenter · hypocenter depth
An instrument that detects and records ground movement caused by earthquakes and other vibrations. The record it produces is called a seismogram.
Where you use it
Strictly, the seismometer is the sensor and the seismograph is the whole recording system, but people often use the words interchangeably. Seismographs work in networks; in Turkey, AFAD and Kandilli Observatory run national networks.
Examples
Seismographs hundreds of kilometres away recorded the explosion.
Each seismograph station sends its data to the centre in real time.
Common phrases
seismograph station · seismograph network · recorded by seismographs · seismogram
A series of very long sea waves caused by a sudden movement of the sea floor, usually an undersea earthquake, but sometimes a landslide or volcanic eruption.
Where you use it
A Japanese word used worldwide. A tsunami is generated or triggered and strikes or hits a coast. Warning centres issue tsunami warnings after large undersea earthquakes. In deep water the waves are low and fast; they grow high near the coast.
Examples
The earthquake triggered a small tsunami that flooded the harbour.
If the sea suddenly pulls back from the shore, a tsunami may be coming.
Usage note
Do not call it a 'tidal wave': tsunamis have nothing to do with tides. Many English speakers do not pronounce the first 't': soo-NAH-mee.
A measure of how strongly an earthquake's shaking is felt and how much damage it causes at a particular place. It usually decreases with distance from the source.
Where you use it
Given in Roman numerals from I (not felt) to XII on scales such as the Modified Mercalli Intensity (MMI) scale or the European Macroseismic Scale (EMS-98). After an earthquake it is shown on intensity maps or shakemaps.
Examples
The intensity reached IX in the town centre but only VI in the nearby villages.
Soft ground can increase the intensity of shaking.
Usage note
Magnitude is one number for the whole earthquake; intensity varies from place to place. Turkish 'şiddet' means intensity, not magnitude.
The likelihood that a given place will experience earthquake shaking of a certain strength within a certain period of time.
Where you use it
Shown on seismic hazard maps and used in building codes. In Turkey, AFAD publishes the Turkey Earthquake Hazard Map, which engineers use in design. Hazard depends on faults and ground conditions; risk also takes buildings and people into account.
Examples
The new hospital was designed for the high seismic hazard in the region.
Seismic hazard is highest near active faults and on soft ground.
Usage note
Hazard and risk are different. Hazard is the chance of strong shaking; risk is the expected loss, which also depends on how many people and weak buildings are exposed.
The process in which loose, water-saturated sand or silt loses its strength during strong earthquake shaking and behaves like a liquid.
Where you use it
A key term in earthquake engineering and engineering geology. Liquefaction can make buildings tilt or sink and cause sand boils at the surface; it was widespread in Adapazarı in 1999. Engineers assess liquefaction potential before building.
Examples
Several buildings tilted because of liquefaction of the sandy ground.
The site investigation showed a high risk of liquefaction near the river.
An opening in the Earth's crust where magma, gas and ash come out, and the mountain or hill built around it by repeated eruptions.
Where you use it
Volcanoes are described as active, dormant or extinct, and by shape: stratovolcano, shield volcano, cinder cone. Volcanologists monitor them with seismometers, gas sensors and satellites. The plural is volcanoes; volcanos is also accepted.
Examples
Mount Ararat and Erciyes are large volcanoes in eastern and central Anatolia.
The volcano has been quiet for centuries, but scientists still monitor it.
Molten or partly molten rock beneath the Earth's surface, often containing crystals and dissolved gases. It is called lava once it reaches the surface.
Where you use it
Used in igneous petrology and volcanology: magma forms, rises, cools, crystallises and erupts. A magma chamber is a large body of magma in the crust. Magmas are described by composition, from basaltic to rhyolitic.
Examples
Magma rising beneath the volcano caused hundreds of small earthquakes.
Silica-rich magma is very viscous and tends to erupt explosively.
Common phrases
magma chamber · rising magma · basaltic magma · magma cools · magma composition
Molten rock that has come out of a volcano onto the Earth's surface, and also the solid rock that forms when it cools.
Where you use it
Lava flows, pours, spreads and cools. Volcanologists talk about lava flows, lava fields and lava domes, and describe basaltic lava as runny and silica-rich lava as sticky. It is usually uncountable, but geologists use 'lavas' for different types.
Examples
The lava flow destroyed several houses but moved slowly enough for people to leave.
The columns in this basalt formed as the lava cooled and shrank.
Usage note
Magma is underground; lava is at the surface. They are the same material in different places.
Common phrases
lava flow · lava field · lava dome · molten lava · basaltic lava
To send out lava, ash and gas, either in a violent explosion or as a quieter flow of lava. Said of volcanoes, and also of geysers.
Where you use it
Used without an object for volcanoes ('the volcano erupted in 1991') and with an object for material ('it erupted ash and lava'). The noun is eruption: an explosive eruption, an eruption column. It is also used figuratively: violence erupted.
Examples
The volcano last erupted about 400 years ago.
If the volcano erupts again, the ash could close the airport.
Usage note
Do not confuse erupt with 'interrupt'. The stress is on the second syllable: e-RUPT.
Common phrases
erupt violently · last erupted · begin to erupt · erupt lava · an explosive eruption
Describing a volcano that is not erupting now and has not erupted for a long time, but is expected to be able to erupt again.
Where you use it
Part of the series active, dormant and extinct. The limits are not exact, and many volcanologists simply call any volcano that could erupt 'active'. The word is also used for seeds, bacteria and inactive accounts.
Examples
The volcano has been dormant for more than 1,000 years.
A dormant volcano can become active again with little warning.
Usage note
'Dormant' means sleeping, not dead. A volcano that will never erupt again is 'extinct'.
A large, bowl-shaped hollow formed when the ground above a magma chamber collapses after a big eruption has emptied the chamber.
Where you use it
Calderas are usually several kilometres across, far larger than a crater, and often fill with water to form lakes. In Turkey, Nemrut volcano near Lake Van has a caldera with lakes inside it. Phrases: caldera collapse, caldera lake, caldera rim.
Examples
The caldera formed when the roof of the magma chamber collapsed.
From the caldera rim you can see two lakes inside the volcano.
Usage note
A crater is the small opening at the top of a volcano; a caldera is a much larger collapse feature. Do not use the two words interchangeably.
Common phrases
caldera collapse · caldera lake · caldera rim · collapse caldera
A fast-moving, ground-hugging cloud of hot gas, ash and rock fragments that rushes down the side of a volcano during an explosive eruption.
Where you use it
The deadliest volcanic hazard: pyroclastic flows can travel at more than 100 km/h at temperatures of several hundred degrees. They killed the people of Pompeii and Herculaneum in AD 79. Their deposits form ignimbrite and tuff.
Examples
Pyroclastic flows swept down the valley and buried the villages.
The soft tuff of Cappadocia was laid down by ancient pyroclastic flows.
Common phrases
pyroclastic flow deposits · pyroclastic density current · deadly pyroclastic flows · pyroclastic material
An area of volcanic activity in the middle of a plate, thought to be fed by a plume of unusually hot rock rising from deep in the mantle.
Where you use it
Hawaii and Yellowstone are the best-known examples. As a plate moves over a hotspot, it leaves a chain of volcanoes that get older with distance. Also written 'hot spot'. Related term: mantle plume.
Examples
The Hawaiian Islands formed as the Pacific Plate moved over a hotspot.
Hotspot volcanoes can form far from any plate boundary.
Usage note
In everyday English a hotspot is also a place with public Wi-Fi, or a busy, popular place.
Tiny fragments of rock, minerals and volcanic glass, less than 2 mm across, blasted into the air by explosive eruptions.
Where you use it
A major hazard: ash clouds damage aircraft engines, and ash falls can collapse roofs and harm crops and lungs. In 2010, ash from Eyjafjallajökull in Iceland closed much of European airspace. Compacted ash forms a rock called tuff.
Examples
Volcanic ash covered the town in a grey layer several centimetres thick.
Pilots must avoid volcanic ash clouds because the ash can stop jet engines.
Usage note
Volcanic ash is not soft like the ash from a fire: it is made of hard, sharp particles of rock and glass.
Common phrases
volcanic ash cloud · ash fall · ash layer · fine volcanic ash
The removal of soil and rock fragments from one place and their transport to another by water, wind, ice or gravity.
Where you use it
Often used with the agent that causes it: river erosion, wind erosion, coastal erosion, soil erosion. The verb is erode and the adjective erosional. Common phrases: prevent erosion, cause erosion, be exposed by erosion.
Examples
Soil erosion is a serious problem on steep, bare slopes.
Millions of years of erosion have exposed the granite at the heart of the mountain.
Usage note
Erosion is not the same as weathering. Weathering breaks rock down where it is; erosion carries the pieces away.
The breaking down of rock at or near the Earth's surface by physical, chemical or biological processes, without the pieces being carried away.
Where you use it
Divided into physical (mechanical) weathering, such as frost wedging, and chemical weathering, such as the dissolving of limestone. In field and engineering reports, rock is described as fresh, slightly weathered or highly weathered.
Examples
Chemical weathering is faster in warm, wet climates.
Break off a piece: weathering has stained the surface, but the rock inside is fresh.
Usage note
Do not confuse it with 'weather' in the sense of rain or sunshine. In geology, 'weathering' always means the breakdown of rock.
Common phrases
chemical weathering · physical weathering · weathered surface · resistant to weathering · deeply weathered
Loose particles such as sand, mud, gravel, shells or plant matter that are carried by water, wind or ice and settle in a new place.
Where you use it
Used in sedimentology, hydrology and environmental work. Sediment is transported, deposited, compacted and eroded. It is countable for types (marine sediments, lake sediments). Engineers worry about sediment filling the reservoirs behind dams.
Examples
The river carries huge amounts of sediment after heavy rain.
We took cores of lake sediment to study the past climate.
The process by which sediment carried by water, wind or ice is dropped and builds up, for example when a river slows down.
Where you use it
Often paired with erosion: 'erosion on the outside of the bend, deposition on the inside'. The verb is deposit and the adjective depositional, as in 'depositional environment', a very common phrase in sedimentology.
Examples
Deposition happens where the current slows down, for example at the mouth of a river.
These sandstones record deposition in an ancient desert.
Usage note
In law, a deposition is a witness's sworn statement taken before a trial. In geology the word is only about sediment.
Common phrases
erosion and deposition · rate of deposition · depositional environment · deposition of sediment
A large, slow-moving mass of ice formed from snow that builds up over many years and flows downhill under its own weight.
Where you use it
Glaciers erode, carry and deposit rock, leaving U-shaped valleys, cirques and moraines. They advance or retreat, and most are retreating today as the climate warms. Ice sheets are glaciers that cover huge areas, such as Antarctica.
Examples
The glacier has retreated almost a kilometre in the last century.
This U-shaped valley was carved by a glacier during the last ice age.
Usage note
Pronounced GLAY-sher in American English and GLASS-ee-uh in British English.
A flat, often fan-shaped area of land built from sediment that a river deposits where it slows down on entering a sea or lake.
Where you use it
Named after the Greek letter Δ because of the shape of the Nile delta. Deltas grow, build out into the sea, or shrink when dams trap sediment upstream. In Turkey, the Kızılırmak, Göksu and Gediz deltas are important wetlands.
Examples
The river delta is advancing into the sea by several metres a year.
Since the dam was built, the delta has been losing land to the sea.
Common phrases
river delta · delta plain · delta front · the Nile delta
The sudden movement of a mass of rock, soil or debris down a slope, often triggered by heavy rain, earthquakes or construction work.
Where you use it
Used in hazard reports, news and engineering geology. Landslides are triggered, block roads and bury houses. Specialists use the wider term 'mass movement' and name types such as rockfalls, slides and debris flows. Landslides are frequent in Turkey's Black Sea region.
Examples
A landslide blocked the main road after three days of heavy rain.
Cutting into the slope for the new road made it more prone to landslides.
Usage note
In everyday English 'landslide' also means an election won by a very large margin.
Common phrases
trigger a landslide · landslide risk · landslide hazard map · a major landslide
To make something gradually thinner, smaller or smoother by rubbing, flowing water or wind, or to become thinner in this way.
Where you use it
A common phrasal verb in textbooks and field talk for describing erosion in simple English. It can take an object (the river wears away the rock) or not (the soft layers wear away faster). Past forms: wore away, worn away.
Examples
Waves are slowly wearing away the base of the cliff.
Soft shale layers wear away faster than the hard sandstone above them.
Usage note
A noun object can go before or after 'away': 'wear the rock away' or 'wear away the rock'. A pronoun must go in the middle: 'wear it away'.
Common phrases
wear away the rock · slowly wear away · worn away by water · wear away over time
The flat land beside a river that is covered with water when the river floods, built up from the fine sediment the river leaves behind.
Where you use it
Floodplains have fertile soils and are often farmed or built on, which increases flood risk. Geologists study floodplain deposits, and planners prepare floodplain maps. It is also written 'flood plain'.
Examples
New houses on the floodplain were badly damaged in the spring floods.
The floodplain is covered with fine silt and clay.
Common phrases
floodplain deposits · river floodplain · build on the floodplain · floodplain map
A landscape formed when water slowly dissolves soluble rocks such as limestone or gypsum, creating caves, sinkholes, underground rivers and large springs.
Where you use it
Used as a noun and as an adjective: karst landscape, karst aquifer, karst spring. Typical landforms are sinkholes (dolines), poljes and caves. Karst is widespread in Turkey's Taurus Mountains, and the large sinkholes of the Konya region are called obruk.
Examples
Rivers often disappear underground in karst areas.
Pollution spreads fast through a karst aquifer.
Usage note
The name comes from the Kras region on the border of Slovenia and Italy, where these landforms were first studied in detail.
The loose top layer of the land surface, made of weathered rock particles, organic matter, water and air, in which plants grow.
Where you use it
Used in soil science, agriculture, ecology and engineering. Soils are described by texture, colour, depth and fertility. In civil engineering, 'soil' means any loose ground above bedrock and is studied in soil mechanics.
Examples
The volcanic soils around the mountain are very fertile.
The engineers tested the soil before designing the foundations.
Usage note
Turkish has two words: 'toprak' for soil scientists and farmers, 'zemin' for engineers. English uses 'soil' for both.
The upper layer of soil, usually the top 5 to 30 cm, which is rich in organic matter and holds most plant roots and soil organisms.
Where you use it
Used in agriculture, soil conservation and construction. Topsoil is lost, washed away, eroded, or stripped before building work. Because it forms very slowly, losing it to erosion is a serious problem.
Examples
Heavy rain washed away the topsoil from the ploughed slopes.
The contractor stripped the topsoil and stored it for later use.
Common phrases
loss of topsoil · fertile topsoil · strip the topsoil · topsoil erosion
A vertical section through a soil from the surface down to the rock beneath, showing its different layers, called horizons.
Where you use it
Soil scientists dig a soil pit or use a road cut to describe a soil profile, recording the depth, colour, texture and structure of each horizon. Profiles are compared to classify soils and judge how old and well developed they are.
Examples
We dug a pit to describe the soil profile down to 1.5 metres.
A mature soil profile shows clear horizons from top to bottom.
Common phrases
describe a soil profile · soil profile description · soil pit · a well-developed soil profile
One of the distinct layers in a soil profile, roughly parallel to the surface, that differs from the others in colour, texture or composition.
Where you use it
Named with letters: O (organic layer), A (topsoil), E (leached layer), B (subsoil), C (weathered parent material) and R (bedrock). Students learn to say 'the B horizon is rich in clay'. Often shortened to 'horizon'.
Examples
In this pit, the soil horizon below the topsoil is rich in clay.
Each soil horizon is described by its colour, texture and thickness.
Common phrases
A horizon · B horizon · soil horizon boundary · organic horizon
The dark, stable organic material in soil that forms when plant and animal remains decay. It holds water and nutrients and makes soil fertile.
Where you use it
Used in soil science, agriculture and gardening. Humus gives topsoil its dark colour. Soils are described as humus-rich or humus-poor, and the process that forms humus is called humification.
Examples
Forest soils often have a thick layer of humus.
Adding compost increases the humus content of the soil.
Usage note
Do not confuse it with hummus, the chickpea dip, which Turkish also calls 'humus'. Soil humus is pronounced HYOO-mus; the food is HUM-us.
The proportions of sand, silt and clay particles in a soil, which control how well it holds water, how it drains and how easily it can be worked.
Where you use it
Measured in the lab or estimated by hand in the field, then named with the soil texture triangle: sandy, loamy, silty, clayey. Loam, a balanced mix, suits most crops. Do not confuse texture with soil structure, the way particles clump together.
Examples
Rub a moist sample between your fingers to estimate the soil texture.
Soil texture affects how quickly water drains after irrigation.
Very fine mineral particles, smaller than about 0.002 mm in soil science, and the soft, sticky material they form when wet. Clay holds water and nutrients well.
Where you use it
Has two meanings: a particle size and a group of minerals (clay minerals such as kaolinite and smectite). Used in soil science, sedimentology and engineering, where clays can swell, shrink or become unstable. The adjective is clayey.
Examples
The clay layer stops water from draining, so the field floods easily.
The rock or loose sediment from which a soil develops through weathering. Its minerals strongly affect the soil's texture, colour and fertility.
Where you use it
One of the classic soil-forming factors, together with climate, organisms, relief and time. Parent material may be the bedrock below the soil or sediment brought by rivers, wind or glaciers. In a soil profile it corresponds to the C horizon.
Examples
Soils developed on basalt parent material are often dark and fertile.
Here the parent material is river sediment, not the bedrock below.
Common phrases
soil parent material · parent material and climate · weathered parent material · soil-forming factors
The continuous movement of water between the oceans, the atmosphere and the land through evaporation, condensation, precipitation and runoff.
Where you use it
Used from school science to university hydrology courses. Technical texts also call it the hydrological or hydrologic cycle. Students describe its stages and explain how water is stored in oceans, ice, groundwater and lakes.
Examples
Groundwater is the slowest part of the water cycle.
A warmer climate speeds up the water cycle.
Common phrases
the water cycle · hydrological cycle · stages of the water cycle · the global water cycle
Water held underground in the pores and cracks of soil, sediment and rock below the water table. It feeds wells and springs.
Where you use it
Used in hydrogeology, water management and environmental reports. Groundwater is pumped, extracted, recharged, polluted or depleted. It is usually written as one word.
Examples
Over-pumping of groundwater has lowered the water table across the plain.
Water that falls from clouds to the ground as rain, snow, sleet or hail. It is usually measured in millimetres per day, month or year.
Where you use it
The technical word for what most people call rain or snowfall. Used in meteorology, hydrology and climate reports: annual precipitation, heavy precipitation, precipitation data. It is one of the main stages of the water cycle.
Examples
Annual precipitation here is less than 300 mm.
Most precipitation in the region falls as snow in winter.
Usage note
In chemistry and geochemistry, precipitation also means a solid forming out of a solution, for example calcite precipitating from cave water.
Common phrases
annual precipitation · heavy precipitation · precipitation data · average precipitation
An underground body of permeable rock or sediment that holds groundwater and lets it flow, so that it can supply wells and springs.
Where you use it
A key word in hydrogeology. Sand, gravel, sandstone and fractured limestone make good aquifers. Aquifers are recharged, tapped, contaminated or overexploited. A confined aquifer lies between impermeable layers; an unconfined aquifer is open to the surface.
Examples
The city gets most of its drinking water from a limestone aquifer.
Fertiliser from the fields is slowly contaminating the shallow aquifer.
The whole area of land from which rainwater and snowmelt flow into one river and its tributaries, separated from neighbouring basins by higher ground.
Where you use it
Used in hydrology, water management and geomorphology. British English also says catchment or catchment area; American English often says watershed. The boundary between two basins is the drainage divide.
Examples
The Kızılırmak drainage basin covers a large part of central Anatolia.
Pollution anywhere in the drainage basin can end up in the river.
Usage note
In British English 'watershed' traditionally means the dividing line between basins, while in American English it usually means the basin itself.
Common phrases
drainage basin area · river drainage basin · drainage divide · catchment area
The upper surface of groundwater, below which soil and rock are fully saturated with water. Its depth rises and falls with rainfall and pumping.
Where you use it
Used in hydrogeology, agriculture and construction: a high water table, a falling water table, the water table drops. The zone above it is the unsaturated zone. Engineers check the water table before digging foundations or tunnels.
Examples
The water table has dropped by 20 metres because of over-pumping.
In spring, the water table is only a metre below the surface.
Common phrases
a high water table · the water table drops · a falling water table · depth to the water table
Water from rain or melting snow that flows over the ground surface into streams and rivers instead of soaking into the soil.
Where you use it
Used in hydrology, agriculture and environmental reports: surface runoff, stormwater runoff, agricultural runoff. Runoff increases on paved, bare or saturated ground and can carry soil, fertiliser and pollutants. The noun is one word; the verb is 'run off'.
Examples
Concrete surfaces in cities increase runoff and the risk of flash floods.
Runoff from the farms carries nitrates into the lake.
The process in which liquid water turns into water vapour and rises into the air, mainly from oceans, lakes, rivers and wet soil, driven by the Sun's heat.
Where you use it
A key stage of the water cycle. Hydrologists measure evaporation with evaporation pans and combine it with plant transpiration as evapotranspiration. When seawater evaporates in shallow basins, it leaves salt deposits called evaporites.
Examples
In summer, evaporation from the lake is greater than the water flowing in.
These thick salt layers formed by evaporation of an ancient sea.
Common phrases
rate of evaporation · evaporation and transpiration · high evaporation · evaporation pan
Allowing water or other fluids to pass through easily. Sand, gravel and cracked limestone are permeable, while clay and shale let very little water through.
Where you use it
Used in hydrogeology, engineering and petroleum geology. The opposite is impermeable and the noun is permeability. Permeable layers form aquifers, while impermeable layers can trap groundwater, oil and gas beneath them.
Examples
Rain soaks quickly into the permeable sandy soil.
The aquifer is a permeable sandstone between two layers of clay.
Usage note
Permeable is not the same as porous. Clay is very porous and holds a lot of water, but its pores are so tiny that water hardly moves through it.
The typical weather of a region over a long period, usually averaged over 30 years, including temperature, rainfall and wind.
Where you use it
Used in geography, geology and environmental science. Climates are described as arid, humid, temperate, Mediterranean or continental. Geologists also study past climates (palaeoclimate) using rocks, ice cores and fossils.
Examples
Central Anatolia has a dry continental climate with cold winters.
These coal layers show that the climate here was once warm and wet.
Usage note
Climate is the long-term average; weather is what happens today. 'The climate is rainy today' is wrong; say 'the weather is rainy today'.
Common phrases
Mediterranean climate · climate change · arid climate · past climate · climate zone
The state of the atmosphere at a particular place and time, such as temperature, wind, cloud, humidity and precipitation over hours or days.
Where you use it
Used in meteorology, fieldwork planning and daily life: weather forecast, weather conditions, bad weather, weather station. 'Weather' is uncountable: 'the weather was bad', never 'a bad weather'.
Examples
We cancelled the field trip because of bad weather in the mountains.
Check the weather forecast before you go out to the outcrop.
Usage note
Weather and whether sound the same. Never use 'a' with weather: say 'bad weather' or 'a spell of bad weather'.
Common phrases
weather forecast · weather conditions · bad weather · weather station · extreme weather
The layer of gases surrounding the Earth, held in place by gravity. It is mostly nitrogen and oxygen, and weather happens in its lowest layer, the troposphere.
Where you use it
Used in climate science, meteorology and planetary science. Its layers are the troposphere, stratosphere, mesosphere and thermosphere. Earth scientists treat the atmosphere, hydrosphere, biosphere and geosphere as connected systems.
Examples
Large volcanic eruptions can send fine ash high into the atmosphere.
The ozone layer lies in the stratosphere, the second layer of the atmosphere.
The warming of the Earth's surface because gases such as water vapour, carbon dioxide and methane absorb heat given off by the ground and send part of it back down.
Where you use it
A natural effect that keeps the Earth's average surface temperature at around 15 °C instead of about -18 °C. Human emissions strengthen it, so scientists speak of an enhanced greenhouse effect. Related terms: greenhouse gases, emissions, global warming.
Examples
Without the natural greenhouse effect, the Earth would be frozen.
Rising carbon dioxide levels are strengthening the greenhouse effect.
Common phrases
greenhouse gases · the natural greenhouse effect · enhanced greenhouse effect · greenhouse gas emissions
The amount of water vapour in the air, usually given as relative humidity: the percentage of the maximum amount the air can hold at that temperature.
Where you use it
Used in weather reports and meteorology: high humidity, low humidity, a relative humidity of 80%. It is measured with a hygrometer. Warm air can hold more water vapour than cold air, so humidity is closely linked to temperature, cloud and dew.
Examples
Humidity on the Black Sea coast is high for most of the year.
Relative humidity drops in the afternoon as the air warms up.
The boundary between two air masses with different temperature and humidity. When a cold or warm front passes, it often brings cloud, rain and a change in wind.
Where you use it
Used in weather forecasts and meteorology: a cold front, a warm front, an occluded front; a front moves in, passes through or brings rain. On weather maps, cold fronts are drawn with triangles and warm fronts with semicircles.
Examples
A cold front will bring heavy rain and a sharp drop in temperature tomorrow.
The warm front passed overnight, and the morning was mild and cloudy.
Common phrases
cold front · warm front · occluded front · a front moves in · frontal system
The pressure caused by the weight of the air above a surface. At sea level it averages about 1013 hectopascals, and it falls as you go higher.
Where you use it
Also called air pressure or barometric pressure; measured with a barometer in hectopascals (hPa) or millibars. Forecasters talk about high pressure, which usually brings settled weather, and low pressure, which brings cloud and rain.
Examples
Atmospheric pressure falls as you climb a mountain.
A rapid drop in atmospheric pressure usually means a storm is coming.
Usage note
One hectopascal equals one millibar, so '1013 hPa' and '1013 mb' are the same value.
Common phrases
high pressure · low pressure · air pressure · barometric pressure · sea-level pressure
A long period in Earth's history when global temperatures were low and large ice sheets covered parts of the continents. The last glacial period ended about 11,700 years ago.
Where you use it
In everyday use, 'the Ice Age' means the most recent cold period. Scientists distinguish glacial periods, which are cold, from interglacials, which are warmer, like today. Evidence comes from glacial landforms, sediments and ice cores.
Examples
During the last ice age, sea level was more than 100 metres lower than today.
These boulders were carried here by ice during an ice age.
Usage note
Strictly speaking, we still live in an ice age, because there are ice sheets on Antarctica and Greenland; today is a warmer interglacial within it.
Common phrases
the last ice age · during an ice age · glacial period · interglacial period
A place where bedrock appears at the surface, not covered by soil or plants, so that geologists can see and study it directly.
Where you use it
A key fieldwork word. Geologists visit, describe, sketch, photograph and sample outcrops; road cuts and quarries often provide good ones. It is also a verb: 'limestone outcrops along the coast'.
Examples
The best outcrop of the formation is in the road cut north of the village.
Describe the outcrop carefully before you take any samples.
Common phrases
describe an outcrop · outcrop scale · a fresh outcrop · road-cut outcrop · poor outcrop
A map that shows which rock units occur at or just below the surface, together with their ages, boundaries, faults, folds and strike and dip measurements.
Where you use it
Called a geologic map in the US. Students learn to read the legend, draw cross-sections and make their own geological maps at field camp. In Turkey, the General Directorate of Mineral Research and Exploration (MTA) publishes them at several scales.
Examples
According to the geological map, the village is built on alluvium.
Your final task at field camp is to produce a geological map of the area.
Common phrases
geological map legend · produce a geological map · geological map sheet · geological cross-section
A detailed map that shows the shape and height of the land using contour lines, together with rivers, roads, buildings and other features.
Where you use it
The base map for most fieldwork: geologists plot their observations on a topographic map before drawing a geological map. Common phrases: topographic map sheet, a 1:25,000 topographic map, read a topographic map. 'Topo map' is informal.
Examples
Mark each sample location on your topographic map.
On this topographic map, the contour interval is 10 metres.
Common phrases
topographic map sheet · read a topographic map · base map · 1:25,000 topographic map
A line on a map joining points of equal height above sea level. Lines that are close together show a steep slope; widely spaced lines show gentle ground.
Where you use it
Often just 'contour': the 500 m contour. The height difference between neighbouring lines is the contour interval. Students practise drawing profiles from contour lines and recognising valleys and ridges.
Examples
The contour lines are very close together here, so expect a steep climb.
Where contour lines form a V pointing uphill, there is usually a valley.
Common phrases
contour interval · index contour · draw contour lines · the 500 m contour
Work done outdoors at real sites, such as observing, measuring, mapping and sampling rocks, soils or rivers, rather than in a laboratory or office.
Where you use it
Central to geology degrees, which include field trips, field courses and a field camp or mapping project. People do, carry out or plan fieldwork; 'in the field' means at the site. Observations go into a field notebook.
Examples
We spent three weeks doing fieldwork in the Taurus Mountains.
Fieldwork starts at seven, so bring water, a hat and your hand lens.
Usage note
'Fieldwork' is uncountable: say 'a lot of fieldwork' or 'a period of fieldwork', not 'a fieldwork'.
Common phrases
do fieldwork · carry out fieldwork · fieldwork season · field trip · field notebook
Two measurements that describe the orientation of a rock layer or fault: strike is the compass direction of a horizontal line on it, and dip is its angle of tilt.
Where you use it
Measured in the field with a geological compass and clinometer, written in the notebook and plotted on maps with a T-shaped symbol. Written in different styles, such as '045/30 SE' or 'N45E, 30SE'. Dip is always measured at right angles to strike.
Examples
Measure the strike and dip of the bedding at every outcrop.
The strike and dip readings on both sides of the valley show that the beds are folded.
Usage note
Turkish speakers may link 'dip' with the Turkish word 'dip' (bottom) or with English 'deep'. In geology, dip is an angle measured in degrees, not a depth.
Common phrases
measure strike and dip · strike and dip symbol · dip angle · dip direction · strike line
The ratio between a distance on a map and the real distance on the ground. On a 1:25,000 map, 1 cm on paper equals 250 m on the ground.
Where you use it
Shown as a ratio (1:50,000), a scale bar or in words. Read '1:25,000' as 'one to twenty-five thousand'. Field geologists often map at 1:10,000 or 1:25,000. The word also describes the size of what you observe: outcrop scale, regional scale.
Examples
We mapped the area at a scale of 1:10,000.
Always include a scale bar on your field sketches.
Usage note
A large-scale map (such as 1:5,000) shows a small area in great detail; a small-scale map (such as 1:1,000,000) shows a large area with little detail. Many learners get this the wrong way round.
Common phrases
map scale · large-scale map · small-scale map · scale bar · at a scale of
A small amount of rock, soil, water or sediment collected so that it can be described, tested or analysed in a laboratory.
Where you use it
Geologists collect, label, bag and analyse samples. Common types: hand sample (a fist-sized piece of rock), core sample, soil sample, water sample. Each sample needs a number, location, date and description in the field notebook. Also a verb: we sampled the outcrop.
Examples
Take a fresh sample from below the weathered surface.
The water samples were sent to the lab for chemical analysis.
Common phrases
take a sample · hand sample · rock sample · sample number · sample location
Ten questions from this glossary. Pick the right meaning for each term and see your score.
How to learn geology & earth sciences vocabulary
Learn words in families: erode, erosion and erosional; deposit, deposition and depositional; sediment, sedimentary and sedimentation; volcano, volcanic and volcanism. Papers switch between these forms all the time.
Read real texts from the field: earthquake reports from seismology centres, the legends and explanatory notes of geological maps, field guides, textbook chapters and the abstracts of research articles. They show how the terms are used in context.
Learn the Greek and Latin building blocks: geo- (earth), litho- (rock), hydro- (water), seismo- (shaking), -sphere (layer or shell) and -logy (study of). They unlock hundreds of terms at once.
Practise describing a rock or an outcrop aloud in English: colour, grain size, minerals, layering, fossils, strike and dip. Keep at least part of your field notebook in English.
Watch the Turkish traps: kaya, kayaç and taş; toprak and zemin; plaka and levha; and the decimal comma. Turkish writes '7,2 büyüklüğünde', but English writes 'magnitude 7.2'.
Frequently asked questions
What is the difference between geology, earth science and geoscience?
Geology studies the solid Earth: rocks, minerals, structures and the history recorded in them. Earth science is the wider umbrella that also covers the oceans, the atmosphere, water and climate. Geoscience is mostly a synonym of earth science and is common in job titles and university department names.
Should I say 'rock' or 'stone' in geology?
Use 'rock' for the natural material and for rock types: igneous rock, a rock sample, the rock cycle. 'Stone' is used for cut building material, gemstones and some fixed names such as limestone, sandstone and kidney stone. Turkish geologists make a similar choice between 'kayaç' for a rock type and 'kaya' or 'taş' in everyday speech.
What is the difference between earthquake magnitude and intensity?
Magnitude measures the size of the earthquake at its source, so one earthquake has one magnitude, written with Arabic numerals such as 6.4. Intensity describes how strongly the shaking was felt and what damage it caused at a particular place, so it changes from town to town and is written with Roman numerals such as VIII. Turkish uses 'büyüklük' for magnitude and 'şiddet' for intensity, and the two are often confused in news reports.
How do I read ages and dates such as 'Ma' in geology texts?
Ma stands for mega-annum, meaning millions of years ago: '66 Ma' is read 'sixty-six million years ago'. Ga means billions of years and ka thousands of years. Some authors use 'Myr' or 'm.y.' for a length of time rather than a date, for example 'the eruption lasted 2 Myr'. Turkish texts often write 'My' for 'milyon yıl'.
Do Turkish geologists use English terms in their work?
Yes. Most of the scientific literature they read is in English, theses include an English abstract, and international projects, conferences and field camps use English. Many Turkish terms are also borrowed from French or English, such as fay, magma, lav, rift and karst, so learning the English originals often makes the Turkish clearer too.
