EARS 5 – Natural Disasters & Catastrophes: Vocabulary Review

100 key vocabulary flashcards summarizing fundamental terms, concepts, and phenomena from the EARS 5 lecture notes on natural disasters, plate tectonics, earthquakes, and volcanoes.

Natural Disaster

A naturally occurring event that causes significant destruction of life or property.

Catastrophe

A natural event that kills or injures large numbers of people or causes extensive property damage.

Hazard

The probability that a natural phenomenon will occur in a given region and time period.

Risk

The probability of adverse consequences (loss, injury, damage) resulting from a natural phenomenon.

Mitigation

Strategies designed to minimize risk, including prediction, prevention, preparedness, and regulation.

Recurrence Interval

Statistical estimate of the average time between events of a given magnitude.

Fractal

A geometric pattern that looks similar at many different scales; used to describe natural features such as coastlines or river networks.

Plate Tectonics

Theory describing the large-scale movement of Earth’s lithospheric plates.

Lithosphere

The rigid outer shell of Earth, consisting of crust and uppermost mantle.

Asthenosphere

Weak, ductile layer of the upper mantle that flows slowly beneath the lithosphere.

Crust

Earth’s outermost solid layer; divided into continental and oceanic types.

Continental Crust

Thick, low-density, felsic crust averaging 20–70 km in thickness.

Oceanic Crust

Thin, dense, mafic crust roughly 5–8 km thick, primarily basalt.

Mantle

Thick layer of peridotite rock between crust and core; mostly solid but convects slowly.

Core

Central iron-nickel portion of Earth; outer core liquid, inner core solid.

Moho (Mohorovičić Discontinuity)

Boundary between crust and mantle marked by a sudden increase in seismic velocities.

Geologic Time

Immense span of Earth’s history, measured in billions of years.

Half-Life

Time required for half the atoms of a radioactive parent isotope to decay to daughter products.

Radioactive Decay

Spontaneous transformation of unstable atomic nuclei, used for isotopic dating.

Uranium-Lead Dating

Radiometric method that uses decay of 238U → 206Pb (and 235U → 207Pb) to date old rocks.

Carbon-14 Dating

Technique for dating recent organic material using the 14C → 14N decay (half-life ~5,700 yr).

Significant Figures

Digits in a number that convey its measurement precision.

Precision

Degree to which repeated measurements give the same result.

Accuracy

Degree to which a measurement agrees with the true or accepted value.

Divergent Boundary

Plate boundary where plates move apart and new lithosphere forms.

Convergent Boundary

Plate boundary where plates collide; features subduction or continental collision.

Transform Boundary

Plate boundary where plates slide past each other horizontally.

Mid-Ocean Ridge

Underwater mountain chain formed at divergent boundaries by seafloor spreading.

Subduction Zone

Region where one plate descends beneath another into the mantle.

Hotspot

Stationary mantle plume that generates volcanic activity within a plate.

Shield Volcano

Broad, gently sloping volcano built by low-viscosity basaltic lava flows (e.g., Hawaii).

Stratovolcano (Composite Volcano)

Steep-sided volcano built of alternating lava flows and pyroclastics, common at subduction zones.

Cinder Cone

Small, steep volcanic cone composed mostly of scoria and other pyroclasts.

Caldera

Large volcanic depression formed by collapse after a massive eruption.

Basaltic Magma

Low-silica, low-viscosity magma that typically erupts peacefully.

Andesitic Magma

Intermediate-silica magma often associated with explosive subduction-zone volcanism.

Rhyolitic Magma

High-silica, high-viscosity magma prone to highly explosive eruptions.

Viscosity

Resistance of a fluid to flow; increases with silica content and decreases with temperature.

Volatile Content

Amount of dissolved gases (H₂O, CO₂, SO₂) in magma; controls explosivity.

Magma

Molten or partially molten rock beneath Earth’s surface.

Lava

Magma that erupts onto Earth’s surface.

Tephra

All airborne pyroclastic material ejected by a volcano.

Pyroclastic Flow

Hot, fast-moving density current of gas and volcanic fragments.

Lahar

Mudflow composed of volcanic ash and water, often following eruptions or heavy rain.

Ash Fall

Fine volcanic particles that settle from an eruption cloud over large areas.

Bomb (Volcanic)

Ejected chunk of semi-molten lava > 64 mm in diameter that solidifies in flight.

Lapilli

Volcanic fragments 2–64 mm across ejected during an eruption.

Liquefaction

Loss of soil strength due to earthquake shaking of water-saturated sediments.

Amplification (Seismic)

Increase in shaking intensity caused by soft surface materials.

Seismograph

Instrument that records ground motion during earthquakes.

Seismogram

Paper or digital record produced by a seismograph showing wave arrivals.

Epicenter

Point on Earth’s surface directly above an earthquake’s focus.

Hypocenter (Focus)

Actual location within Earth where earthquake rupture starts.

P Wave (Primary)

Fastest compressional body wave; travels through solids, liquids, and gases.

S Wave (Secondary)

Slower shear body wave; travels only through solids.

Rayleigh Wave

Surface wave with retrograde elliptical particle motion in a vertical plane.

Love Wave

Surface wave with horizontal shear motion perpendicular to propagation.

Surface Wave

Seismic wave confined to Earth’s surface; arrives after body waves and often causes most damage.

Seismic Moment (M₀)

Physical measure of earthquake size: rock rigidity × rupture area × slip.

Moment Magnitude (Mw)

Scale based on seismic moment; uniformly measures very small to giant earthquakes.

Richter Magnitude (ML)

Original scale using maximum seismic amplitude at 100 km to estimate earthquake size.

Modified Mercalli Scale

Qualitative scale (I–XII) describing earthquake intensity based on observed effects.

Elastic Rebound Theory

Model stating that earthquakes occur when accumulated elastic strain is released by sudden fault slip.

Fault Scarp

Step-like surface feature produced by vertical displacement along a fault.

Hanging Wall

Block of rock above an inclined fault plane.

Footwall

Block of rock below an inclined fault plane.

Normal Fault

Dip-slip fault where the hanging wall moves down relative to the footwall.

Reverse Fault

Dip-slip fault where the hanging wall moves up relative to the footwall.

Strike-Slip Fault

Fault with primarily horizontal movement parallel to strike of the fault.

Right-Lateral

Sense of strike-slip motion where the opposite block moves to the right.

Left-Lateral

Sense of strike-slip motion where the opposite block moves to the left.

Seismic Shadow Zone

Area on Earth’s surface that does not receive direct P or S waves due to core refraction or absorption.

P-Wave Shadow

103°-142° distance zone that lacks direct P waves owing to outer-core refraction.

S-Wave Shadow

Zone beyond 103° where no S waves arrive because they cannot travel through the liquid outer core.

Tsunami

Sea wave generated by submarine earthquake, landslide, or eruption; long wavelength, high speed.

Landslide

Downslope movement of rock or soil triggered by gravity, often induced by earthquakes or rain.

Wildfire

Uncontrolled fire in vegetation-rich areas; considered a natural disaster type.

Drought

Prolonged period of deficient precipitation resulting in water shortage; a climatological hazard.

Geophysical Event

Natural disaster category including earthquakes, volcanic activity, and tsunamis.

Meteorological Event

Disaster category including storms such as hurricanes and tornadoes.

Hydrological Event

Disaster type involving floods and mass movements like landslides.

Climatological Event

Disaster category involving extreme temperatures, drought, and wildfires.

Risk Perception

Public or individual judgment about the severity and probability of a risk.

Seismic Gap

Segment of an active fault known to produce earthquakes but that has been quiet for an unusually long time.

GPS Plate Motion

Measurement of plate velocity and direction using global positioning system receivers.

Magnetic Stripe (Seafloor)

Symmetric bands of normal and reversed magnetism recording seafloor spreading.

Hypsographic Curve

Graph showing distribution of Earth’s surface elevations relative to sea level.

Blue Book Activity

In-class written exercise used for formative assessment in EARS 5.

Disaster Movie Paper

Course assignment critiquing the scientific accuracy of a disaster film.

Modified Curve Grading

Course policy in which final grades follow an adjusted statistical distribution, not negotiable.

Moment-Energy Relation

Formula log E = 11.8 + 1.5 Mw giving seismic energy in ergs from moment magnitude.

East African Rift

Active zone of continental extension marked by normal faulting and basaltic volcanism.

Yellowstone Hotspot

Continental mantle plume responsible for rhyolitic calderas and the Snake River Plain track.

Flood Basalt

Extensive plateau-forming eruption of very fluid basaltic lava from fissures.

Decompression Melting

Partial melting caused by pressure release as hot mantle rises without significant cooling.

Water-Aided Melting

Partial melting triggered by addition of volatiles from a subducting slab into overlying mantle.

Pyroclastic Flow Deposit

Layered rock formed by emplacement of hot, dense pyroclastic material.

Seismic Amplification

Increase in ground motion due to soft sediments relative to bedrock.

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