Physical Geography – Vocabulary Flashcards

Core vocabulary covering Earth origin, interior, plate dynamics, geomorphic processes, oceanography and related physical-geography concepts.

Nebular Hypothesis

Theory that the Sun and planets formed from a rotating cloud of gas and dust that contracted and flattened into a disk.

Big Bang Theory

Model that the universe began ~13.7 billion years ago from an extremely dense, hot singularity that has been expanding ever since.

Geological Timescale

Chronological framework dividing Earth’s 4.6 Ga history into eons, eras, periods, epochs and ages.

Lithosphere

Rigid outer shell comprising the crust and uppermost mantle; broken into tectonic plates.

Asthenosphere

Partially molten, ductile upper mantle layer (≈100–200 km deep) that allows plates to move.

Isostasy

State of gravitational balance in which Earth’s crust ‘floats’ at an elevation dependent on its thickness and density.

Convection Current Theory

Arthur Holmes’ idea that heat-driven mantle convection drags tectonic plates across Earth’s surface.

Continental Drift

Wegener’s concept that present continents were once joined as Pangaea and have since moved apart.

Plate Tectonics

Unifying theory explaining crustal motion by interaction of lithospheric plates at divergent, convergent and transform boundaries.

Divergent Boundary

Plate margin where plates move apart and new oceanic crust forms, e.g. Mid-Atlantic Ridge.

Convergent Boundary

Margin where plates collide causing subduction, mountain building or island arcs.

Transform Fault

Plate boundary where plates slide horizontally past each other, e.g. San Andreas Fault.

Seafloor Spreading

Process by which magma rises at mid-ocean ridges creating new basaltic crust that moves ocean floors outward.

Mid-Ocean Ridge

World-encircling submarine mountain chain formed at divergent boundaries with a central rift valley.

Mantle Plume

Column of hot, buoyant mantle rock that rises and may generate hotspot volcanism.

Hotspot

Stationary surface expression of a mantle plume producing volcanic chains as plates drift over it (e.g. Hawaii).

Shield Volcano

Broad, gently sloping volcano built by fluid basaltic lava flows; effusive eruptions.

Stratovolcano (Composite)

Steep-sided volcano of alternating lava and pyroclast layers; viscous magma, explosive eruptions.

Cinder Cone

Small, steep volcanic cone made of loose pyroclastic fragments ejected from a single vent.

Caldera

Large depression formed when a volcano’s summit collapses after a massive eruption empties the magma chamber.

Earthquake

Sudden release of accumulated stress along faults producing ground shaking and seismic waves.

Focus (Hypocentre)

Point within the Earth where seismic energy is first released during an earthquake.

Epicentre

Point on Earth’s surface directly above an earthquake focus where shaking is first felt.

P-Wave (Primary)

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

S-Wave (Secondary)

Slower transverse body wave that passes only through solids, producing shear motion.

Shadow Zone

Earth-surface belt receiving no direct P or S waves due to refraction (P) and liquid core blockage (S).

Richter Scale

Logarithmic measure of earthquake magnitude based on seismic wave amplitude.

Moment Magnitude (Mw)

Modern magnitude scale based on fault area, slip and rock rigidity; accurate for large quakes.

Modified Mercalli Scale

12-grade scale that expresses earthquake intensity by observed effects on people, structures and land.

Weathering

In-situ breakdown of rocks by physical disintegration and chemical decomposition at Earth’s surface.

Solution (Chemical Weathering)

Process whereby soluble minerals dissolve in water, removing material from rock.

Carbonation

Weathering in which carbonic acid dissolves carbonate minerals such as limestone and dolomite.

Hydration (Weathering)

Addition of water molecules to mineral structure causing expansion and disintegration (e.g. anhydrite → gypsum).

Oxidation

Chemical weathering by reaction of minerals with oxygen, producing oxides and weakening rock.

Frost Wedging

Mechanical weathering where water in cracks freezes, expands and splits rock.

Exfoliation

Peeling of outer rock layers due to pressure release or thermal expansion, forming domes and sheets.

Mass Movement

Downslope transfer of weathered material by gravity without flowing water as the transporting medium.

Landslide

Rapid, perceptible movement of dry rock or soil mass down a slope under gravity.

Debris Flow (Mudflow)

Fast flow of water-saturated soil and rock fragments moving as a viscous fluid on slopes or channels.

Alluvial Fan

Cone-shaped deposit of coarse sediments spread by mountain streams where gradient suddenly decreases.

Delta

Triangular deposit at a river mouth where sediment loads exceed wave and tidal removal.

Oxbow Lake

Crescent-shaped water body cut off from a meandering river when a meander loop is abandoned.

Karst Topography

Landscape on soluble rocks (limestone) characterised by sinkholes, caves, disappearing streams and towers.

Stalactite

Icicle-like dripstone hanging from cave ceilings formed by precipitation of calcium carbonate.

Stalagmite

Cone-shaped calcite deposit built upward from cave floors beneath stalactites.

Sinkhole (Doline)

Depression or hole in carbonate terrain formed by dissolution or roof collapse of a cave.

Cirque

Amphitheatre-shaped hollow at a glacier head produced by frost action and ice plucking.

Arête

Sharp knife-edge ridge formed between two adjacent glacial cirques.

U-Shaped Valley

Broad, flat-floored valley carved by glacial erosion, replacing a former V-shaped river valley.

Fjord

Deep, steep-walled, glacial trough now inundated by the sea.

Moraine

Ridge or blanket of unsorted glacial till deposited directly by ice.

Drumlin

Streamlined, elongated hill of glacial till with blunt stoss end and tapered lee end indicating ice flow.

Continental Shelf

Gently sloping, submerged extension of a continent from shoreline to shelf break (~100-200 m deep).

Continental Slope

Steeper seaward edge of a continent descending from shelf break to deep-sea floor.

Abyssal Plain

Extensive, flat, deep-ocean floor at 3–6 km depth blanketed by fine sediments.

Thermocline

Ocean layer of rapid vertical temperature decline separating warm surface water from cold deep water.

Salinity

Total concentration of dissolved salts in seawater, averaged at 35 ‰ (parts per thousand).

Spring Tide

Highest tidal range occurring at full and new moon when Sun, Earth and Moon align.