Valencian Community PAU Geology and Environmental Sciences flashcards

34 cards. Read the term and the definition here. The deck at the top of this page is optional.

Moho discontinuity

Boundary between the Earth's crust and mantle, identified by an increase in seismic wave velocity at roughly 30-70 km depth beneath continents and 5-10 km beneath oceans.

S-wave shadow zone

Region beyond about 103 degrees from an earthquake epicentre where transverse S waves are not recorded, because they cannot pass through the liquid outer core.

Isostasy

State of gravitational equilibrium in which the lithosphere floats on the denser asthenosphere; Airy and Pratt models explain crustal roots and density compensation respectively.

Wadati-Benioff zone

Inclined plane of earthquake foci marking a subducting oceanic slab, extending to about 700 km depth where the slab remains cold and brittle.

Seafloor magnetic stripes

Symmetrical bands of normal and reversed magnetisation in oceanic crust on either side of a mid-ocean ridge, recording geomagnetic reversals and supporting seafloor spreading.

Ophiolite

Fragment of oceanic lithosphere obducted onto continental crust during collision, comprising serpentinite, gabbro, sheeted dykes and pillow basalts in sequence.

Bowen's reaction series

Sequence in which minerals crystallise from cooling magma: olivine, pyroxene, amphibole, biotite, then feldspars, muscovite and quartz at lower temperatures.

Porphyritic texture

Igneous texture with large crystals (phenocrysts) set in a finer groundmass, indicating two-stage cooling: slow crystallisation at depth followed by rapid cooling near the surface.

Metamorphic isograd

Line on a map joining points of equal metamorphic grade, defined by the first appearance of an index mineral such as garnet or kyanite in a rock sequence.

Faunal succession principle

Fossil assemblages change in a definite, recognisable order through stratified rocks, allowing correlation of strata of the same age across wide areas.

Angular unconformity

Erosion surface where tilted or folded older strata are overlain by younger, near-horizontal beds, indicating deformation followed by erosion and renewed deposition.

K-Pg extinction

Mass extinction about 66 million years ago ending the Cretaceous, linked to the Chicxulub impact and marked by an iridium anomaly and loss of ammonites and dinosaurs.

Karst dolines

Closed depressions formed by dissolution of limestone, ranging from small solution pits to large poljes; sinkholes may collapse suddenly and pose engineering hazards.

Hjulström curve

Graph relating stream velocity to particle size, showing the velocity needed to erode, transport or deposit sediment; clay needs high velocity to erode because of cohesion.

Cross-bedding

Inclined internal layers within a sedimentary bed, formed by migrating dunes or ripples; the dip direction indicates the direction of the depositing current.

Mohs hardness scale

Relative scale from 1 (talc) to 10 (diamond) ranking minerals by scratch resistance; quartz is 7, calcite 3, and a fingernail is about 2.5.

Coal rank

Progressive increase in carbon content and calorific value through peat, lignite, sub-bituminous coal, bituminous coal and anthracite, driven by heat and pressure during burial.

Gangue

Non-economic minerals associated with an ore body, such as quartz or calcite, which must be separated from the valuable ore during mineral processing.

Moment magnitude Mw

Scale measuring earthquake size from the seismic moment, related to fault area, slip and rock rigidity; it is logarithmic and does not saturate for very large events.

Lahar

Volcanic mudflow of ash, rock and water that travels rapidly down valleys, often generated when eruptions melt snow or heavy rain mobilises loose pyroclastic deposits.

Factor of safety slope

Ratio of resisting shear strength to driving shear stress on a potential failure surface; values above one indicate stability, below one indicate likely failure.

Greenhouse effect

Process whereby atmospheric gases absorb outgoing infrared radiation and re-emit it, warming the surface; without it Earth's mean temperature would be about minus 18 degrees Celsius.

Milankovitch cycles

Long-term variations in Earth's orbit and axis, namely eccentricity, obliquity and precession, which alter insolation distribution and pace glacial-interglacial cycles.

El Niño Southern Oscillation

Coupled ocean-atmosphere oscillation in the tropical Pacific; El Niño brings warm water eastward, disrupting rainfall, fisheries and weather patterns worldwide.

Darcy's law

Groundwater discharge equals hydraulic conductivity times cross-sectional area times hydraulic gradient; it describes laminar flow through porous aquifer material.

Artesian aquifer

Confined aquifer in which the potentiometric surface lies above the top of the aquifer, so water rises in a well without pumping when the surface is above ground level.

Eutrophication

Nutrient enrichment of water by nitrogen and phosphorus, causing algal blooms, oxygen depletion, fish kills and loss of ecological quality in lakes and coastal waters.

Carrying capacity K

Maximum population size an ecosystem can sustain indefinitely given available resources; logistic growth slows as population approaches this limit.

Soil horizons

Vertical layers of a soil profile: O organic litter, A topsoil with humus, B illuviation zone, C weathered parent material and R bedrock.

Nitrogen fixation

Conversion of atmospheric nitrogen into ammonia by bacteria such as Rhizobium or by lightning and industrial processes, making nitrogen available to living organisms.

Photochemical smog

Secondary pollutant mixture of ozone, aldehydes and PAN formed when nitrogen oxides and hydrocarbons react under sunlight, typical of warm cities with heavy traffic.

Environmental Impact Assessment

Procedure predicting environmental effects of a proposed project before approval, including scoping, baseline study, impact prediction, mitigation measures, public consultation and monitoring.

True dip and strike

Strike is the compass direction of a horizontal line on a bedding plane; true dip is the maximum inclination measured perpendicular to strike, seen in cross-section.

X-ray diffraction analysis

Laboratory technique identifying minerals from the pattern of X-rays diffracted by their crystal lattices, especially useful for fine-grained or mixed samples.