IEB Grade 12 Geography: Climatology, Fluvial Geomorphology, and Economic Geography

Comprehensive vocabulary flashcards covering South African climatology, fluvial geomorphology, and agricultural economic geography for Grade 12 IEB students.

Isobars

Lines connecting places of equal atmospheric pressure on a synoptic chart, where the spacing indicates pressure gradient wind strength.

High Pressure (Anticyclones)

Atmospheric systems where pressure increases toward the center (e.g., $1024\text{\text{ hPa}}$), characterized by subsiding, diverging air masses and absolute atmospheric stability.

Low Pressure (Cyclones)

Atmospheric systems where pressure decreases toward the center (e.g., $1000\text{\text{ hPa}}$), characterized by ascending, converging air currents and highly unstable weather fronts.

Wind Velocity Plotting (Full Feather)

A symbol on a wind vector shaft representing a speed of $10\text{\text{ knots}}$.

Wind Velocity Plotting (Pennant Triangle)

A symbol on a wind vector shaft designating a speed of $50\text{\text{ knots}}$.

Mid-Latitude Cyclones (MLCs)

Massive low-pressure wave systems ($1000\text{--}3000\text{\text{ km}}$ in scale) moving West to East, driven by prevailing Westerlies, typically delivering winter rainfall to the Western Cape.

Tropical Cyclones (TCs)

Intense cyclonic systems ($100\text{--}500\text{\text{ km}}$ scale) manifesting over warm tropical ocean corridors ($> 26.5^\text{o}C$) during late summer to autumn.

The Eye

The absolute calm, cloudless core of a Tropical Cyclone consisting of subsiding air.

Eye Wall

The symmetrical area surrounding the Eye of a Tropical Cyclone featuring massive convective cumulonimbus towers.

Coastal Lows

Localized, shallow low-pressure cells that migrate along the coastline ahead of cold fronts, driving rapid wind shifts and marine fog.

Moisture Front / Trough

A summer phenomenon where warm humid air from the South Indian High collides with cool dense air from the South Atlantic High over the interior plateau.

Line Thunderstorms

Volatile, linear convective structures created along the Moisture Front zone.

Intertropical Convergence Zone (ITCZ)

The planetary convergence belt where the North-East and South-East Trade Winds meet, shifting dynamically with the Earth's thermal equator.

Berg Winds

Dominant winter winds created when the Kalahari High forces dry plateau air down the Great Escarpment, heating adiabatically at approximately $1^\text{o}C$ per $100\text{\text{ meters}}$.

Anabatic Winds

Daytime local winds where solar radiation heats upper valley slopes, causing air to expand, become less dense, and flow up the slopes.

Katabatic Winds

Nighttime local winds where terrestrial longwave radiation cools upper slopes, causing dense air to flow down into the valley floor under gravity.

Thermal Belt

A stable temperature inversion midway up valley sides produced when cold katabatic currents displace warmer air upward.

Frost Pockets

Cold pools of air on the valley floor that can drop below $0^\text{o}C$, affecting crop placement.

Topographic Aspect

The orientation of a slope; in the Southern Hemisphere, north-facing slopes receive direct insolation and are warmer and drier than south-facing slopes.

Catchment Area

The geographic basin bounded by a perimeter highland ridge (watershed) that sheds precipitation into a single master drainage system.

Watershed (Interfluve)

A perimeter highland ridge that bounds a catchment area.

Water Table

The baseline level below which a waterbody is saturated.

Dendritic Drainage Pattern

A tree-like, branching configuration developing on horizontally uniform, homogeneous sedimentary or igneous rock structures.

Trellis Drainage Pattern

A pattern where main channels run parallel and secondary tributaries strike at precise $90^\text{o}$ angles, dictated by alternating hard and soft rock layers.

Rectangular Drainage Pattern

A pattern with sharp right-angle bends controlled by jointing frameworks or fault lines in highly fractured basement rock.

Radial Drainage Pattern

A pattern where channels radiate outward and downward from a single elevated dome or volcanic peak.

Strahler's Stream Ordering Method

A numerical classification where two channels of order $n$ merge to form a channel of order $n+1$, while intersections with lower-order streams do not increment the value.

Laminar Flow

A mechanical regime where water layers slide smoothly in parallel sheets, requiring perfectly smooth, straight artificial channels.

Turbulent Flow

A chaotic mechanical regime producing swirling eddies and vertical vectors, dominant in natural streams with rough, boulder-strewn beds.

Longitudinal Profile

The side-view cross-section of a river channel traced from its source to its marine base level.

Outer Bank (Undercut Slope)

The part of a meander where centrifugal force drives maximum velocity and erosion, creating a steep river cliff.

Inner Bank (Slip-off Slope)

The part of a meander where water velocity drops, triggering deposition of bedload to form a gentle point bar.

Oxbow Lake

An isolated loop abandoned by a river when it cuts directly through a meander neck during high-discharge flood stages.

Stream Capture (River Piracy)

When an energetic stream breaches its watershed boundary via headward erosion and intercepts the flow of an adjacent, less energetic stream.

Misfit Stream

The lower remaining remnant of a captured stream that is severely under-fit for its large, pre-existing valley floor.

Elbow of Capture

The sharp, high-angle physical bend marking the exact site of structural diversion during stream capture.

Wind Gap

The newly exposed, abandoned gravel-filled dry valley segment downstream of the elbow of capture.

River Rejuvenation

An increase in a graded river's vertical kinetic energy caused by a drop in regional base level or tectonic uplift, leading to downward cutting.

Knickpoint

A waterfall marking the intersection of old and new graded curves within a rejuvenated river system.

Food Security

When all individuals, at all times, have physical, social, and economic access to sufficient, safe, and nutritionally optimal food sources.