Glossary
Every key term from every chapter in plain language, with a link back to the chapter that teaches it. 233 terms so far.
233 terms from 23 chapters
A
Abrasion
Mechanical wear caused by particles grinding and colliding against one another as they are moved.
Weathering and SoilAftershocks
Smaller earthquakes on the same fault that follow the main shock, sometimes for months.
EarthquakesAir mass
A large body of air with fairly uniform temperature and humidity, taken from the region where it formed.
Pressure, Wind, and Air MassesAir pressure
The weight of the atmosphere pressing on a surface, measured with a barometer in millibars or inches of mercury.
Pressure, Wind, and Air MassesAphelion
The point in an orbit farthest from the sun, where an orbiting body moves slowest.
Gravity, Orbits, and the Solar SystemApparent motion
The perceived movement of the sun, moon, and stars across the sky, caused by Earth's own motions.
Earth's Motions and SeasonsArid
A dry climate, where mechanical weathering dominates and slopes stay steep and angular.
LandscapesAsteroid
A rocky object orbiting the sun, most found in the belt between Mars and Jupiter.
Gravity, Orbits, and the Solar SystemAsthenosphere
The hot, soft (but still solid) layer of the mantle below the lithosphere. It flows very slowly, letting the plates above it move.
Earth's Interior
B
Barometer
The instrument that measures air pressure.
Pressure, Wind, and Air MassesBasalt
A fine, dark extrusive igneous rock. It floors the oceans. The Palisades cliffs across the Hudson are a thick sill of its coarse-grained intrusive twin, diabase.
The Three Rock FamiliesBasaltic
Made of basalt, the dark, dense volcanic rock that forms oceanic crust and erupts as runny lava at divergent boundaries and hot spots.
Plate BoundariesBig Bang
The model of the universe beginning in a hot, dense state about 13.8 billion years ago and expanding ever since.
Stars and the Universe
C
Calcite
The soft mineral of limestone and marble, identified instantly by fizzing in dilute acid.
MineralsCaldera
A broad basin left when the ground collapses into a drained magma chamber after an enormous eruption. Crater Lake and Yellowstone sit in calderas.
VolcanoesCementation
Minerals precipitating from groundwater and gluing sediment grains together into solid rock.
The Three Rock FamiliesChemical weathering
The breakdown of rock by changing its minerals into new substances through reactions with water, air, and acids.
Weathering and SoilCinder cone
A small, steep volcano built from lava fragments during a single short eruption.
VolcanoesClastic
Sedimentary rock made of broken rock fragments cemented together, named by particle size from shale up to conglomerate.
The Three Rock FamiliesCleavage
A mineral's tendency to break along flat planes where its internal bonds are weakest. Mica peels into sheets; halite breaks into cubes.
MineralsClimate
The long-term pattern of weather at a location: its averages of temperature and precipitation and their annual range.
ClimateClimate change
The ongoing shift in Earth's climate driven by rising greenhouse gas concentrations from human activity.
Human Impact and SustainabilityCold front
A front where advancing cold air forces warm air steeply upward, bringing brief heavy showers, then cooler clear air.
Fronts, Station Models, and StormsComet
An icy body on a highly eccentric orbit that grows a glowing tail, always pointing away from the sun, when it nears the sun.
Gravity, Orbits, and the Solar SystemCompaction
The squeezing of buried sediments under the weight of layers above, the first step in turning sediment to rock.
The Three Rock FamiliesComposite volcano
A steep cone built from alternating layers of lava and ash at a subduction zone. Also called a stratovolcano. Fuji and Rainier are examples.
VolcanoesCondensation
Water vapor changing into liquid water, which happens when air cools to its dew point and forms dew, fog, or cloud.
The Atmosphere and MoistureCondensation nuclei
Tiny floating particles of dust, salt, and smoke that water vapor condenses onto to form cloud droplets.
The Atmosphere and MoistureConduction
The transfer of heat by direct contact, molecule to molecule; how heat moves through solids and into the air touching the ground.
The Atmosphere and MoistureContinental climate
A climate deep inside a landmass, with hot summers, cold winters, and a large annual range.
ClimateContinental crust
The thick, lower-density granitic crust that makes up the continents, about 2.7 g/cm3. Too buoyant to subduct.
Plate BoundariesContour interval
The difference in elevation between adjacent contour lines on a map.
Topographic MapsContour line
An isoline of equal elevation on a topographic map.
Topographic MapsConvergent boundary
A boundary where two plates move toward each other, producing subduction zones, trenches, volcanoes, or folded mountains.
Plate BoundariesCoriolis effect
The apparent curving of winds and currents caused by Earth's rotation; deflection is to the right in the Northern Hemisphere.
Pressure, Wind, and Air MassesCorrelation
Matching rock layers from different locations by rock type, marker layers, or fossils.
Geologic HistoryCosmic background radiation
The faint glow arriving from every direction in space: the cooled afterglow of the early universe and key Big Bang evidence.
Stars and the UniverseCross-cutting relationships
The principle that a fault or intrusion is younger than every rock layer it cuts through.
Geologic HistoryCrust
Earth's thin, solid outer skin: granitic rock under continents (about 35 km thick) and denser basaltic rock under oceans (often under 10 km).
Earth's InteriorCrystal
A solid whose atoms repeat in an orderly internal pattern. That hidden pattern is what gives every mineral its properties.
MineralsCrystallization
The growth of mineral crystals as magma or lava cools, the process that forms igneous rock.
The Rock CycleCyclic change
A change that repeats in a regular, predictable pattern, such as tides, seasons, and moon phases.
Observations and Measurement
D
Dendritic drainage
A tree-like, branching drainage pattern that forms on uniform, flat-lying bedrock.
LandscapesDensity
The mass of a substance per unit volume (D = m/V). A property of the substance itself, unchanged by sample size.
Observations and MeasurementDeposition
The dropping of transported sediment when the agent carrying it loses energy.
Erosion and DepositionDew point
The temperature to which air must cool to become saturated. A high dew point means moist air.
The Atmosphere and MoistureDirect relationship
A relationship in which both variables increase together, graphing as a line that slopes upward.
Observations and MeasurementDivergent boundary
A boundary where two plates move apart. Magma rises into the gap and hardens into new oceanic crust.
Plate BoundariesDoppler effect
The shift in wavelength caused by motion: compressed toward the blue when approaching, stretched toward the red when receding.
Stars and the UniverseDrainage pattern
The shape a stream system makes when viewed from above, which reflects the underlying bedrock.
LandscapesDynamic equilibrium
The steady overall shape a landscape holds when uplifting forces and leveling forces are in balance, even as rock moves through it.
Landscapes
E
Earthquake
Shaking of the ground caused by the sudden release of stored energy when rock breaks and slips along a fault.
EarthquakesEccentricity
How stretched an ellipse is: the distance between the foci divided by the length of the major axis. Zero is a perfect circle.
Gravity, Orbits, and the Solar SystemEclipse
The alignment of sun, Earth, and moon so one body passes through another's shadow: lunar at full moon, solar at new moon.
The MoonEffusive
An eruption style in which runny lava flows out steadily rather than exploding.
VolcanoesElastic rebound
The snap of bent, stressed rock back toward its original shape when it finally breaks, releasing stored energy as an earthquake.
EarthquakesElectromagnetic spectrum
The full range of light energy, from long radio waves to short gamma rays, with visible light as a thin slice.
Stars and the UniverseElevation
Height of the land above sea level.
LandscapesEpicenter
The point on Earth's surface directly above an earthquake's focus. It is the location reported in the news.
EarthquakesEquinox
The days, about March 21 and September 23, when the sun is overhead at the equator and day and night are equal everywhere.
Earth's Motions and SeasonsErosion
The transport of weathered material away from its source by an agent such as running water, glaciers, wind, or waves.
Erosion and DepositionErratic
A boulder carried by a glacier and left stranded far from its source rock.
Erosion and DepositionExtrusive
Igneous rock that cooled quickly at the surface, leaving crystals too small to see, like basalt.
The Three Rock Families
F
Fault
A crack in Earth's crust along which blocks of rock have moved. Transform boundaries are giant faults.
EarthquakesFeldspar
The most abundant mineral family in Earth's crust, with blocky cleavage in two directions at about 90 degrees.
MineralsFelsic
High-silica, light-colored, lower-density igneous composition (granite, rhyolite). The explosive end of the ESRT igneous chart.
VolcanoesField
A region in which a quantity such as elevation or temperature has a measurable value at every point.
Locating Points on EarthFocus
The point underground where an earthquake actually begins, on the fault where the rock broke.
EarthquakesFoliation
The banding or alignment of minerals in a metamorphic rock, produced as pressure forces crystals to line up.
The Three Rock FamiliesFracture
Breaking with rough or curved surfaces instead of flat planes, as quartz and garnet do.
MineralsFront
The boundary where two different air masses meet, where clouds and precipitation concentrate.
Fronts, Station Models, and StormsFrost wedging
Mechanical weathering in which water freezes in a crack, expands, and pries the rock apart over repeated freeze-thaw cycles.
Weathering and Soil
G
Galaxy
An enormous system of billions of stars held together by gravity. The sun belongs to the Milky Way galaxy.
Stars and the UniverseGarnet
A hard, glassy, usually deep red mineral with no cleavage. New York's official state gemstone, mined in the Adirondacks.
MineralsGeocentric model
The historical Earth-centered model of the universe, replaced because it could not simply explain planetary motions.
Gravity, Orbits, and the Solar SystemGeologic time scale
The calendar of Earth history, divided into eons, eras, periods, and epochs based on the fossil record.
Geologic HistoryGraded bedding
A sediment layer that grades from coarse at the bottom to fine at the top, a signature of deposition by water.
Erosion and DepositionGradient
How rapidly a field value changes with distance: change in value divided by distance. Steep slopes have high gradients.
Topographic MapsGranite
A coarse, light-colored intrusive igneous rock of feldspar, quartz, and mica. The classic continental rock.
The Three Rock FamiliesGravity
The attractive force between all masses. It grows with mass and weakens rapidly with distance.
Gravity, Orbits, and the Solar SystemGreenhouse effect
The warming of Earth's surface by atmospheric gases that let sunlight in but absorb outgoing infrared radiation.
Human Impact and SustainabilityGreenhouse gas
A gas such as water vapor, carbon dioxide, or methane that absorbs and re-radiates outgoing infrared energy.
Human Impact and Sustainability
H
Hachures
Short tick marks on a closed contour loop pointing inward, marking a depression rather than a hill.
Topographic MapsHalf-life
The time required for half of a radioactive parent isotope in a sample to decay into its daughter product.
Geologic HistoryHardness
A mineral's resistance to being scratched, ranked 1 to 10 on the hardness scale from talc to diamond.
MineralsHeliocentric model
The sun-centered model of the solar system, in which the planets, including Earth, orbit the sun on ellipses.
Gravity, Orbits, and the Solar SystemHot spot
A fixed zone of rising hot mantle rock that melts through the moving plate above it, building a chain of volcanoes such as Hawaii.
VolcanoesHumid
A wet climate, where chemical weathering and vegetation round the land into gentle, soil-covered slopes.
LandscapesHumus
The dark organic material in soil formed from decayed plants and animals.
Weathering and SoilHurricane
An intense tropical low-pressure storm powered by heat from warm ocean water, weakening quickly over land.
Fronts, Station Models, and StormsHydrolysis
A chemical weathering reaction in which water changes feldspar into clay.
Weathering and Soil
I
Igneous rock
Rock formed when molten magma or lava cools and crystallizes. Crystal size records the cooling speed.
The Three Rock FamiliesIndex contour
A darker contour line, usually every fifth one, labeled with its elevation to make the map faster to read.
Topographic MapsIndex fossil
A fossil of an organism that was geographically widespread but existed for a short time, ideal for correlating and dating layers.
Geologic HistoryInertia
The tendency of a moving object to keep moving in a straight line. Together with gravity, it produces orbits.
Gravity, Orbits, and the Solar SystemInference
An interpretation or conclusion drawn from observations rather than observed directly.
Observations and MeasurementInner core
The solid iron-nickel sphere at Earth's center. Hotter than the outer core, but kept solid by extreme pressure.
Earth's InteriorIntensity
How strong the shaking felt and how much damage occurred at a particular place. It decreases with distance from the epicenter.
EarthquakesIntrusive
Igneous rock that cooled slowly underground, growing crystals large enough to see, like granite.
The Three Rock FamiliesInverse relationship
A relationship in which one variable increases as the other decreases, graphing as a line or curve that slopes downward.
Observations and MeasurementIsland arc
A curved chain of volcanic islands, such as Japan or the Aleutians, built above a subduction zone where two oceanic plates converge.
Plate BoundariesIsobar
An isoline connecting points of equal air pressure on a weather map.
Locating Points on EarthIsoline
A line on a map connecting points with the same field value. Isolines never cross.
Locating Points on EarthIsotherm
An isoline connecting points of equal temperature on a weather map.
Locating Points on Earth
L
Lahar
A volcanic mudflow of ash mixed with water or meltwater that races down river valleys, sometimes long after an eruption.
VolcanoesLake-effect snow
Heavy snow dropped downwind of a lake when cold dry air picks up moisture crossing the warmer water.
ClimateLandscape
The shape of Earth's surface in a region: its hills, valleys, ridges, and flats.
LandscapesLandscape region
An area with similar landscape characteristics because it shares the same bedrock and structure. Boundaries between regions are usually abrupt.
LandscapesLatitude
Angular distance north or south of the equator, from 0 to 90 degrees. In the Northern Hemisphere it equals the altitude of Polaris.
Locating Points on EarthLava
Magma that has erupted onto Earth's surface.
VolcanoesLeeward
The downwind side of a mountain range, where sinking air warms and dries.
ClimateLeveling forces
Weathering and erosion, which wear the land down and carry material away.
LandscapesLight-year
The distance light travels in one year, about 9.5 trillion kilometers; the working unit of cosmic distance.
Stars and the UniverseLithification
The turning of loose sediment into solid sedimentary rock through compaction and cementation.
The Rock CycleLithosphere
Earth's rigid outer shell, about 100 km thick: the crust plus the uppermost mantle. The tectonic plates are pieces of lithosphere.
Earth's InteriorLongitude
Angular distance east or west of the prime meridian, from 0 to 180 degrees.
Locating Points on EarthLuminosity
The true brightness of a star: the total energy it gives off.
Stars and the UniverseLuster
How a mineral's surface reflects light: metallic like polished metal, or nonmetallic (glassy, pearly, dull). The first fork in the ESRT mineral chart.
Minerals
M
Mafic
Low-silica, dark, denser igneous composition rich in iron and magnesium (basalt, gabbro). The runny, quiet end of the chart.
VolcanoesMagma
Molten rock beneath Earth's surface. Its silica and gas content decide how it erupts.
VolcanoesMagnetic field
The field generated by currents in the liquid outer core. It steers compasses and shields Earth from solar radiation.
Earth's InteriorMagnitude
A number describing the energy an earthquake releases. Each whole step up represents about 32 times more energy.
EarthquakesMain sequence
The band on the star chart where stars spend most of their lives fusing hydrogen, the sun included.
Stars and the UniverseMantle
The thick layer of solid silicate rock between the crust and the core, nearly 2,900 km deep. Its slow convection drives plate motion.
Earth's InteriorMantle convection
The slow overturning of the mantle as hot, less dense rock rises and cooler, denser rock sinks. It is the engine behind plate motion.
Plate BoundariesMantle plume
The rising column of unusually hot mantle rock that feeds a hot spot.
VolcanoesMarble
Metamorphosed limestone: interlocking calcite crystals that still fizz in acid, with the fossils erased.
The Three Rock FamiliesMarine climate
A climate moderated by a nearby large body of water: cooler summers, milder winters, small annual range.
ClimateMass movement
The downhill movement of rock and soil under the pull of gravity, such as landslides and slumps.
Erosion and DepositionMeasurement
An observation expressed as a number with a unit, such as grams or degrees Celsius.
Observations and MeasurementMechanical weathering
Physical breakup of rock into smaller pieces without changing its minerals. Also called physical weathering.
Weathering and SoilMetamorphic rock
Rock changed by intense heat and pressure without melting, often showing banding or aligned crystals.
The Three Rock FamiliesMeteor
The streak of light produced when a fragment from space burns through Earth's atmosphere.
Gravity, Orbits, and the Solar SystemMeteorite
A fragment from space that survives its passage through the atmosphere and lands on Earth's surface.
Gravity, Orbits, and the Solar SystemMeteorites
Rocky and metallic leftovers from the early solar system. Iron meteorites hint at the composition of Earth's core.
Earth's InteriorMica
A family of minerals with one perfect cleavage direction, so they peel into thin, flexible, shiny sheets.
MineralsMid-latitude cyclone
A large low-pressure system with cold and warm fronts spiraling counterclockwise around it; the main storm system of the middle latitudes.
Fronts, Station Models, and StormsMid-ocean ridge
A long underwater mountain chain that forms at a divergent boundary, with a rift valley at its center where new crust is made.
Plate BoundariesMineral
A naturally occurring, inorganic solid with a definite chemical composition and a crystalline structure. Ice qualifies; coal and glass do not.
MineralsMoon phase
The changing appearance of the moon's lit portion through its 29.5-day cycle.
The MoonMoraine
A ridge or mound of till marking the edge or former reach of a glacier. Long Island's two ridges are moraines.
Erosion and Deposition
N
Nonrenewable resource
A resource that forms far too slowly to be replaced as it is used, such as fossil fuels and ores.
Human Impact and SustainabilityNuclear fusion
The joining of light atomic nuclei, hydrogen into helium in stars, converting mass into the energy that powers them.
Stars and the Universe
O
Observation
Information gathered directly by the senses or by instruments that extend them.
Observations and MeasurementOccluded front
The front formed when a fast cold front overtakes a warm front and lifts the warm air entirely off the ground.
Fronts, Station Models, and StormsOcean current
A large stream of moving ocean water. Warm currents flow away from the equator; cool currents flow toward it.
ClimateOceanic crust
The thin, dense, basaltic crust under the oceans, with a density of about 3.0 g/cm3. It subducts when it collides with continental crust.
Plate BoundariesOrbit
The elliptical path of one body around another, with the central body at one focus of the ellipse.
Gravity, Orbits, and the Solar SystemOre
A mineral deposit rich enough to mine at a profit, such as galena for lead or magnetite for iron.
MineralsOrigin time
The moment an earthquake actually happened at the focus, found by working backward from wave arrival times.
EarthquakesOriginal horizontality
The principle that sediment is deposited in flat layers, so tilted layers were deformed after deposition.
Geologic HistoryOuter core
The liquid layer of molten iron and nickel from about 2,900 to 5,150 km deep. It blocks S-waves and generates Earth's magnetic field.
Earth's InteriorOxidation
A chemical weathering reaction between minerals and oxygen, such as iron rusting.
Weathering and Soil
P
P-waves
Primary waves: fast compression waves that pass through solids and liquids and always arrive first at a seismograph.
EarthquakesPangaea
The supercontinent that contained nearly all of Earth's land about 250 million years ago, before plate motion split it apart.
Plate BoundariesParent rock
The original rock that a metamorphic rock formed from: limestone becomes marble, sandstone becomes quartzite, shale becomes slate.
The Three Rock FamiliesPercent deviation
How far a measurement misses the accepted value: the difference divided by the accepted value, times 100.
Observations and MeasurementPerihelion
The point in an orbit closest to the sun, where an orbiting body moves fastest. Earth reaches it in early January.
Gravity, Orbits, and the Solar SystemPlain
A low, flat landscape region with low relief and horizontal bedrock or loose sediment. Also called a lowland.
LandscapesPlate tectonics
The theory that Earth's outer shell is divided into moving plates, and that their motion explains earthquakes, volcanoes, mountains, and the arrangement of the continents.
Plate BoundariesPlateau
A landscape region with high elevation but flat-lying, horizontal bedrock, dissected by streams into hills and valleys.
LandscapesPrecipitation
Any form of water falling from clouds: rain, snow, sleet, or hail.
The Atmosphere and MoisturePrevailing winds
The dominant wind direction of a region. New York sits in the prevailing southwesterlies, so weather moves west to east.
Pressure, Wind, and Air MassesPrime meridian
The 0-degree longitude line through Greenwich, England, from which longitude is measured.
Locating Points on EarthProfile
A side view of the land surface constructed along a line drawn across a contour map.
Topographic MapsPyroclastic flow
A fast avalanche of searing gas, ash, and rock racing down a volcano's flanks. The deadliest volcanic hazard.
Volcanoes
Q
Quartz
Hardness 7, glassy, no cleavage, found nearly everywhere. Its durability is why so many beaches are quartz sand.
Minerals
R
Radial drainage
A drainage pattern with streams flowing outward from a central high point, such as a dome or isolated mountain.
LandscapesRadiation
The transfer of energy by electromagnetic waves, requiring no material; how the sun's energy crosses space to Earth.
The Atmosphere and MoistureRadioactive decay
The steady, spontaneous breakdown of an unstable isotope into a daughter product, used to determine the absolute age of rocks.
Geologic HistoryRain shadow
The dry region on the leeward side of a mountain range.
ClimateRate of change
How quickly a value changes over time: the change in the value divided by the time taken.
Observations and MeasurementRedshift
The stretching of light from distant galaxies toward longer wavelengths, evidence that they are moving away from us.
Stars and the UniverseRelative dating
Placing geologic events in order of occurrence without determining exact ages.
Geologic HistoryRelative humidity
The amount of water vapor in air compared to the maximum it could hold at that temperature, as a percentage.
The Atmosphere and MoistureRelief
The difference in elevation between the highest and lowest points of an area, a measure of how rugged the land is.
LandscapesRenewable resource
A resource replaced by natural processes about as fast as it is used, such as sunlight, wind, and flowing water.
Human Impact and SustainabilityResidual soil
Soil that formed in place, directly from the bedrock beneath it.
Weathering and SoilRevolution
Earth's orbit around the sun, once every 365.25 days.
Earth's Motions and SeasonsRidge push
A driving force of plate motion in which new lithosphere slides downhill off the raised mid-ocean ridge.
Plate BoundariesRift valley
A dropped-down valley that forms where the crust is being stretched and pulled apart at a divergent boundary.
Plate BoundariesRock cycle
The set of processes that continuously changes rock from one type into another. It has no beginning and no fixed order: any rock can become any other.
The Rock CycleRotation
Earth spinning on its axis once every 24 hours, causing day and night and the sky's apparent motion at 15 degrees per hour.
Earth's Motions and Seasons
S
S-waves
Secondary waves: slower side-to-side waves that cannot pass through liquids, which is how they revealed the liquid outer core.
EarthquakesSea breeze
A daytime local wind blowing from water toward land, driven by land heating faster than water.
Pressure, Wind, and Air MassesSeafloor spreading
The process in which new oceanic crust forms at a mid-ocean ridge and moves outward, so the ocean floor gets older with distance from the ridge.
Plate BoundariesSediment
Loose pieces of weathered rock and mineral matter, ranging in size from clay to boulders.
Erosion and DepositionSedimentary rock
Rock built from sediments that were compacted and cemented, from evaporating water, or from the remains of living things. The family that holds nearly all fossils.
The Three Rock FamiliesSeismic waves
Vibrations that carry an earthquake's energy through Earth, including P-waves, S-waves, and surface waves.
EarthquakesSeismogram
The recording a seismograph produces: a trace of ground motion over time, showing the P and S arrivals.
EarthquakesSeismograph
An instrument that detects and records ground shaking.
EarthquakesShadow zone
The parts of Earth's surface where seismic waves from a quake never arrive. S-waves are missing beyond about 103 degrees because the liquid outer core stops them, and refraction at the core boundary leaves a ring from about 103 to 142 degrees with no direct P-waves. Key evidence that the outer core is liquid.
Earth's InteriorShield volcano
A broad, gently sloped volcano built from countless runny basaltic lava flows. Mauna Loa is the classic example.
VolcanoesSilica
The silicon-oxygen compound that makes up most rock. More silica means thicker, stickier, more explosive magma.
VolcanoesSilicate
Rock built from silicon and oxygen, the main ingredient of the crust and mantle.
Earth's InteriorSilicate
A mineral built around silicon and oxygen. Silicates, including quartz, feldspar, and mica, make up most of Earth's crust.
MineralsSlab pull
A driving force of plate motion in which the cold, dense edge of a subducting plate sinks and drags the rest of the plate along. Thought to be the strongest driving force.
Plate BoundariesSoil horizon
A distinct layer in a soil profile, such as topsoil or subsoil, that differs from the layers above and below.
Weathering and SoilSolstice
The days, about June 21 and December 21, when the noon sun is highest or lowest and daylight is longest or shortest.
Earth's Motions and SeasonsSorting
The separation of sediment by size, density, or shape as it is deposited. Water and wind sort; glaciers do not.
Erosion and DepositionStation model
The compact map symbol that records one weather station's temperature, dew point, pressure, wind, and sky conditions.
Fronts, Station Models, and StormsStationary front
A front that has stalled, with neither air mass advancing; often brings long spells of unsettled weather.
Fronts, Station Models, and StormsStrata
The horizontal layers in which sediments are deposited, preserved as the visible beds of sedimentary rock.
The Three Rock FamiliesStreak
The color of a mineral's powder when rubbed on an unglazed tile. More reliable than surface color, which can vary wildly.
MineralsStream velocity
How fast a stream flows. Higher velocity gives the stream more energy to erode and to carry larger particles.
Erosion and DepositionStriations
Parallel scratches carved into bedrock by rock frozen in a moving glacier, showing the direction the ice flowed.
Erosion and DepositionSubduction
The sinking of a denser plate beneath a less dense plate at a convergent boundary, carrying old crust back into the mantle.
Plate BoundariesSupernova
The explosive death of a massive star, which forges and scatters heavy elements and can briefly outshine a galaxy.
Stars and the UniverseSuperposition
The principle that in undisturbed layers the bottom layer is oldest and layers get younger upward.
Geologic HistorySurface waves
The slowest seismic waves, which roll along the ground once energy reaches the surface. They cause most earthquake damage.
EarthquakesSustainability
Meeting present needs without damaging the Earth systems future generations will depend on.
Human Impact and Sustainability
T
Texture
The size, shape, and arrangement of a rock's grains or crystals. Texture is the first clue to which family a rock belongs to.
The Three Rock FamiliesTide
The regular daily rise and fall of ocean water, caused mainly by the moon's gravity.
The MoonTill
Unsorted sediment of all sizes deposited directly by a melting glacier.
Erosion and DepositionTopographic map
A map that shows the shape and elevation of the land using contour lines.
Topographic MapsTornado
A violently rotating column of air extending from a severe thunderstorm to the ground.
Fronts, Station Models, and StormsTransform boundary
A boundary where two plates slide horizontally past each other. Crust is neither created nor destroyed.
Plate BoundariesTransported soil
Soil that was carried in from elsewhere and deposited, such as New York's glacial soils.
Weathering and SoilTrellis drainage
A drainage pattern of parallel main streams with right-angle tributaries, formed where tilted hard and soft layers steer the water.
LandscapesTrench
A deep, narrow depression in the ocean floor that marks where a plate bends downward and subducts.
Plate BoundariesTriangulation
Locating an epicenter by drawing distance circles around at least three stations. The circles intersect at a single point, the epicenter.
EarthquakesTroposphere
The lowest layer of the atmosphere, containing nearly all water vapor and weather.
The Atmosphere and MoistureTsunami
A series of powerful ocean waves generated when an earthquake or landslide suddenly displaces the seafloor.
Earthquakes
U
Unconformity
A buried erosion surface in a rock sequence, representing missing time in the record.
Geologic HistoryUplift
The slow raising of deep rock back toward the surface, driven by Earth's internal heat and plate motion. It keeps the rock cycle from being a one-way trip down.
The Rock Cycle
V
Vent
The opening through which lava, ash, and gas erupt.
VolcanoesVesicular
Full of small holes left by gas bubbles escaping from lava, as in pumice.
The Three Rock FamiliesViscosity
A fluid's resistance to flowing. Low-viscosity magma pours like syrup; high-viscosity magma barely moves and traps gas.
VolcanoesVolcanic arc
A curved chain of volcanoes built on the overriding plate above a subduction zone.
VolcanoesVolcanic ash
Tiny fragments of shattered rock and glass blasted out during explosive eruptions. It collapses roofs, chokes engines, and grounds aircraft.
Volcanoes
W
Warm front
A front where warm air glides up over retreating cold air, bringing widespread, steady precipitation.
Fronts, Station Models, and StormsWeathering
The breakdown of rock, minerals, and soil in place at Earth's surface, without the pieces being carried away.
Weathering and SoilWindward
The side of a mountain range facing the oncoming wind, where rising air cools and precipitates.
Climate
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