Environmental Science: Earth Formation, Tectonics, Hazards, and Earth Surface Systems

A complete set of 101 vocabulary flashcards covering Earth's internal structure, seismic wave propagation, rheology, plate tectonics, hazard geomorphology, and surface rock-weathering systems derived directly from pages 1–26 of the environmental science lecture notes.

Accretion

The gradual growth of an astronomical body as additional particles or objects collide and become incorporated, such as the accumulation of primitive interstellar material into progressively larger bodies during Earth's formation.

Planetesimals

Small bodies of rock or ice produced by accretion that continued colliding and combining to form planets, with some smaller bodies remaining as asteroids.

Accretion Duration of Earth

The estimated period of approximately $30\text{--}40\,\text{million years}$ during which Earth accreted, with metallic material interacting with silicates as the planet differentiated.

Siderophile Elements

'Iron-loving' elements that preferentially associate with metallic iron and were extracted from silicate material into Earth's developing core during differentiation.

Lithophile Elements

Elements with a strong affinity for oxygen that tend to remain in silicate phases, thereby concentrating in the mantle and crust rather than the metallic core.

Core Formation

The segregation process during Earth's growth where heat from impacts and gravity caused extensive melting, allowing metallic cores of incoming planetesimals to break into droplets, sink through silicates, and accumulate into a dense core.

Earth's Core

The dense innermost region of Earth, composed of approximately $80\%$ iron together with nickel, sulfur, and other components, formed by segregation and sinking during early planetary history.

Mantle Silicate Minerals

Common mantle minerals including olivine, garnet, and pyroxene, along with magnesium oxide and elements such as iron, aluminium, calcium, sodium, and potassium.

Outgassing

The release of gases and water previously trapped within Earth's interior, such as through volcanic activity when water escaped with lava as the early mantle cooled.

Seismic Waves

Waves generated by earthquakes that propagate through the planet via elastic deformation, whose arrival times and paths reveal internal boundaries and whether internal regions are solid or liquid.

P-waves (Primary Waves)

Longitudinal, compressional seismic waves that travel through both solids and liquids and travel faster than S-waves, typically arriving first at a seismometer.

S-waves (Secondary Waves)

Transverse shear seismic waves that propagate through solids but cannot travel through liquids, making their absence along certain paths evidence of Earth's liquid interior.

P-wave Velocity Equation

The formula governing the propagation speed of primary seismic waves: $V_p = \sqrt{\frac{K + \frac{4}{3}\mu}{\rho}}$, where $K$ is the bulk modulus, $\mu$ is the shear modulus, and $\rho$ is density.

S-wave Velocity Equation

The formula governing the propagation speed of secondary seismic waves: $V_s = \sqrt{\frac{\mu}{\rho}}$, where $\mu$ is the shear modulus and $\rho$ is density; because liquids cannot sustain shear stress ($\mu = 0$), S-waves do not propagate through them.

Bulk Modulus ($K$)

A physical property expressing a material's resistance to uniform compression, which controls P-wave velocity along with shear modulus and density.

Shear Modulus ($\mu$)

A physical property measuring a material's resistance to shear deformation (rigidity), influencing both P-wave and S-wave velocities.

Giant Impact Hypothesis

The hypothesis stating that early Earth collided with Theia, a Mars-sized body, melting and redistributing material and ejecting debris that subsequently assembled into the Moon.

Mars (Tectonic Inactivity)

The planetary condition resulting from Mars cooling more extensively than Earth, producing a thick, rigid outer shell and reduced internal activity rather than a global plate tectonic system.

Stress

Force acting per unit area on a material, which can act in different directions to produce extension, compression, or shear, leading to translation, rotation, or strain.

Strain

The change in a material's shape or dimensions resulting from deformation in response to applied stress, which may be reversible or permanent.

Tensile Stress

A stress that stretches a material and increases its length, directly associated with extension rather than shortening.

Compressive Stress

A stress that squeezes material, causing it to shorten, and contributing to folding and crustal thickening.

Shear Stress

A stress acting parallel to a surface that tends to distort shape, contrasting with normal stress acting perpendicular to the surface.

Brittle Deformation

Permanent strain where rock fractures or breaks rather than flowing, favored by relatively low temperatures and commonly producing faults.

Ductile Deformation

Permanent bending or flowing of rock without fracturing into separate pieces, favored by higher temperatures that allow minerals to deform plastically.

Elastic Deformation

Reversible deformation in which a material returns to its original dimensions and shape once the applied stress is removed.

Folding

The curving of rock layers during geological deformation, primarily accomplished through the mechanisms of buckling and bending.

Primordial Heat

Thermal energy retained from Earth's formation, comprising energy from accretion, gravitational compression, and differentiation during core formation.

Radiogenic Heat

Thermal energy generated by the radioactive decay of long-lived unstable isotopes, particularly uranium, thorium, and potassium.

Temperature Controls on Rock Deformation

The principle that low temperatures limit atomic mobility and promote brittle fracturing, whereas high temperatures facilitate crystal-plastic flow and ductile deformation.

Continental Drift

The hypothesis proposed by Alfred Wegener in $1912$ asserting that continents move across Earth's surface, supported by the fit of Atlantic coastlines and shared fossil and animal distributions.

Weakness of Wegener's Theory

The lack of an adequate driving mechanism for moving continents, as proposed tidal, gravitational, and centrifugal forces were demonstrated to be insufficient.

Mantle Convection

The tectonic driving mechanism proposed by Arthur Holmes in $1929$, in which thermal energy circulates mantle material to drive plate motion.

Euler's Pole

The fixed point on Earth's spherical surface about which a rigid tectonic plate rotates, with surface points following small-circle paths around it.

Seafloor Spreading

The process occurring at mid-ocean ridges where upwelling mantle material partially melts and cools to create new basaltic oceanic crust, which moves away symmetrically from the ridge.

Symmetrical Magnetic Stripes

Matching bands of alternating magnetic polarity in basalt of equal age on opposite sides of mid-ocean ridges, recognized by Vine and Matthews as evidence of symmetrical seafloor spreading.

Divergent Plate Boundary

A plate margin where tectonic plates move apart and new lithosphere forms at spreading ridges, characterized by basaltic volcanism, crustal extension, and shallow earthquakes.

Convergent Plate Boundary

A plate margin where plates move toward each other, resulting in oceanic lithosphere consumption via subduction (producing trenches, arcs, and earthquakes) or continental collision (forming mountain belts).

Transform Boundary

A plate boundary where tectonic plates slide horizontally past one another without net creation or destruction of crust, typically producing shallow earthquakes.

Passive Continental Margin

The intraplate transition from continental to oceanic lithosphere within a single plate, where thinned crust undergoes isostatic subsidence and accumulates thick sedimentary sequences.

Triple Junction

A tectonic intersection where three plates meet, such as the boundary junction between the African, Eurasian, and Arabian plates.

Slab Pull

The gravitational force exerted when dense, cold oceanic lithosphere sinks into the mantle at a subduction zone, pulling the trailing plate; considered the strongest plate-driving force.

Ridge Push

The gravitational force that drives cooling lithosphere downslope away from elevated mid-ocean ridges.

Mantle Drag

The viscous traction exerted by the moving asthenosphere against the base of a tectonic plate, which can either assist or resist plate motion.

Wilson Cycle

The cyclical process of the opening and closing of ocean basins over geologic time, encompassing rifting, seafloor spreading, subduction, continental collision, and supercontinent reassembly.

Stages of the Wilson Cycle

The six sequential evolutionary phases of ocean basins: embryonic (rift), juvenile (young ocean), mature (wide ocean), declining (subduction), terminal (closing ocean), and suturing (continental collision).

Embryonic Stage (Wilson Cycle)

The initial continental rifting phase characterized by crustal thinning, normal faulting, and rift valley formation, exemplified by the East African Rift separating the Nubian and Somalian plates.

Juvenile Stage (Wilson Cycle)

The early oceanic opening stage where ongoing rifting allows seawater invasion and the inception of seafloor spreading, exemplified by the Red Sea.

Mature Stage (Wilson Cycle)

The evolutionary phase of a wide ocean basin bordered by cooling, subsiding, sediment-rich passive margins, exemplified by the Atlantic Ocean.

Declining Stage (Wilson Cycle)

The phase where subduction consumes oceanic lithosphere, narrowing the ocean basin and generating trenches, volcanic arcs, and earthquakes, exemplified by the Pacific Ocean.

Suturing Stage (Wilson Cycle)

The terminal collision stage where buoyant continents collide after an intervening ocean is consumed, causing crustal thickening, folding, thrust faulting, uplift, and metamorphism, exemplified by the Himalayas.

Subduction (Crustal Recycling)

The sinking of cold, dense oceanic lithosphere into the mantle at subduction zones, recycling oceanic crust while buoyant continental crust resists subduction.

Subduction-Zone Volcanism

Volcanic activity triggered when a descending oceanic slab releases water into the overlying mantle wedge, depressing its melting point and producing magma that forms volcanic arcs.

Earthquake

A sudden ground shaking caused when accumulated tectonic stress overcomes frictional resistance or rock strength, releasing energy as seismic waves.

Subduction-Zone Earthquake Depths

Seismic rupture depths occurring from shallow levels down to approximately $700\,\text{km}$ within a subducting oceanic slab at convergent boundaries.

Earthquake Magnitude

A quantitative measure of the total seismic energy released at the source (focus) of an earthquake.

Earthquake Intensity

A qualitative measure of ground shaking severity and localized damage at a specific location, governed by distance, focal depth, local geology, and structural vulnerability.

Liquefaction

A phenomenon in which water-saturated granular sediment temporarily loses shear strength and behaves as a liquid due to increased pore-water pressure during earthquake shaking.

Effusive Eruptions

Volcanic eruptions featuring hot, low-viscosity basaltic magma that allows gases to escape easily, producing lava flows and broad shield volcanoes.

Explosive Eruptions

Violent volcanic eruptions featuring viscous, silica-rich magma that traps escaping gases until pressure triggers catastrophic fragmentation, producing ash plumes and pyroclastic flows.

Pyroclastic Flow

A high-density, fast-moving, fluidized mixture of extremely hot gas, ash, pumice, and rock fragments expelled during explosive volcanism.

Lahar

A hazardous volcanic mudflow or debris flow composed of saturated pyroclastic debris and water that rapidly descends river valleys from a volcano.

Nevado del Ruiz Hazard ($1985$)

A catastrophic volcanic disaster in $1985$ where a deadly lahar mobilized by eruptive melting of summit ice killed approximately $23{,}000$ people.

Anak Krakatau Flank Collapse ($2018$)

A major volcanic mass-wasting event in $2018$ where the sudden collapse of a volcanic flank into the sea generated a devastating tsunami.

Intraplate Volcanism

Volcanic activity occurring within the interior of tectonic plates away from boundaries, typically driven by mantle plumes (hotspots) that form linear volcanic tracks such as the Hawaiian chain.

Geomorphology

The scientific study of Earth's landforms, the physical and chemical processes that shape them, and the evolution of landscapes over time.

Endogenic Processes

Geological processes driven by Earth's internal thermal energy that construct topographic relief, including tectonic uplift, orogenesis, and volcanism.

Exogenic Processes

Landscape-altering surface processes driven by solar radiation and gravity that wear down relief, including weathering, erosion, mass movement, and sediment transport.

Dynamic Equilibrium

A landscape condition in which overall morphology remains stable over time despite active and continuous transport and throughput of material.

Metastable Equilibrium

A state of apparent landscape stability that can abruptly transition to a new equilibrium state once an external or internal threshold is crossed.

Geomorphic Threshold

The critical boundary condition reached when driving forces overcome resisting forces within a landscape system, triggering an abrupt morphological response such as a landslide.

Positive Feedback (Geomorphology)

A process loop that amplifies and accelerates an initial geomorphic change, such as the progressive self-reinforcing incising of gully erosion.

Negative Feedback (Geomorphology)

A regulatory feedback loop that dampens and counteracts a geomorphic disturbance, promoting stability within a landscape.

Weathering

The physical disintegration, chemical decomposition, or biological breakdown of rock in situ at or near Earth's surface without transporting the material.

Erosion

The detachment, entrainment, and downslope or downwind transport of weathered rock fragments and sediment by dynamic agents such as water, wind, or ice.

Denudation

The long-term lowering and wearing away of Earth's surface through the combined action of weathering, mass wasting, and erosion.

Isostasy

The state of gravitational balance where buoyant crust floats upon the denser underlying mantle, meaning thick mountain ranges possess deep roots and undergo uplift when unloaded by erosion.

Mohr–Coulomb Failure Criterion

The fundamental failure equation determining shear strength on a potential slip plane: $\tau_f = c + \sigma' \tan(\phi)$, where $c$ is cohesion, $\sigma'$ is effective normal stress, and $\phi$ is the internal friction angle.

Cohesion ($c$)

The intrinsic shear strength component of a geological material arising from interparticle bonding and attractive forces, independent of applied normal stress.

Rainfall-Triggered Landslides

Slope instability triggered when heavy precipitation elevates pore-water pressure, which reduces effective normal stress ($\sigma'$) and shear strength along failure surfaces.

Soil Creep

The imperceptibly slow, continuous downslope movement of soil and regolith under the direct influence of gravity, representing a high-frequency, low-magnitude mass wasting process.

Slide vs. Flow

The distinction between a slide, which moves as a relatively coherent block along a well-defined shear surface, and a flow, which undergoes internal shearing and deformation throughout its mass with higher fluid content.

Uplift–Erosion Equation

The mass-balance equation governing landscape topographic elevation: $\Delta z = U - E$, where $\Delta z$ is the change in elevation, $U$ is tectonic uplift rate, and $E$ is erosion rate.

Elevation Evolution Balance

The elevation response where $\Delta z > 0$ (growth) when uplift exceeds erosion ($U > E$), dynamic equilibrium occurs when $U = E$, and surface lowering occurs when $U < E$.

Yellow River Delta

A major coastal depositional feature formed by sediment eroded from northern China, transported by the Yellow River, and deposited into the Bohai Sea as flow decelerates at the coast.

Anthroposphere

The component of Earth's environment created, modified, or managed by human activities and infrastructure, actively interacting with natural Earth systems.

Oceanic Crust

The dense, thin lithospheric layer characterized by an average thickness of about $6\,\text{km}$ and a density of approximately $3.0\,\text{g/cm}^3$.

Continental Crust

The buoyant, thick lithospheric layer characterized by an average thickness of about $40\,\text{km}$ and a density of approximately $2.7\,\text{g/cm}^3$.

Moho Discontinuity

The Mohorovi■i■ discontinuity marking the compositional boundary between the crust and the mantle, recognized by a sharp increase in seismic-wave velocity.

Asthenosphere

The mechanically ductile, highly viscous region of the upper mantle situated beneath the rigid lithosphere, with its upper thermal boundary marked by the $1300^\circ\text{C}$ isotherm.

Three Major Rock Types

The primary lithological classes: igneous (solidification of silicate melt), sedimentary (deposition and lithification of sediment), and metamorphic (solid-state alteration under heat and pressure).

Sedimentary Rock Formation

The sequence of geological processes involving the weathering, erosion, transport, deposition, compaction, and cementation (lithification) of mineral particles.

Metamorphic Rock Formation

The process whereby pre-existing rocks undergo mineralogical, chemical, and structural recrystallization in response to elevated temperatures and pressures without melting.

Freeze–Thaw Weathering

A mechanical weathering process in which water enters rock fractures, freezes, and expands, exerting expansive tensile stresses that fracture the rock without altering its chemistry.

Salt Weathering

A physical weathering mechanism where saline solutions infiltrate rock pores and evaporate, causing growing salt crystals to exert expansive crystallization pressure that breaks rock.

Quartz

A framework silicate mineral ($\text{SiO}_2$) that is exceptionally resistant to chemical weathering and highly stable at Earth's surface conditions, persisting widely in sediments.

Halite

An evaporite mineral ($\text{NaCl}$) that is chemically unstable and highly soluble at Earth's surface, dissolving rapidly upon exposure to water.

Bowen's Reaction Series

A petrological schematic illustrating the predictable crystallization order of silicate minerals from a cooling magma (from high-temperature olivine to low-temperature quartz) and their inverse melting sequence.

Hydrolysis of Potassium Feldspar

A chemical weathering reaction converting potassium feldspar into kaolinite clay while releasing potassium and silicic acid into solution: $2\text{KAlSi}_3\text{O}_8 + 2\text{H}^+ + 9\text{H}_2\text{O} \rightarrow \text{Al}_2\text{Si}_2\text{O}_5(\text{OH})_4 + 2\text{K}^+ + 4\text{H}_4\text{SiO}_4$.

Clay Minerals (in Soil)

Secondary hydrous aluminum phyllosilicates formed by weathering and hydrolysis that regulate soil moisture retention and provide ion-exchange capacity for plant nutrients.