Landforms, Tectonics and Drainage
This domain examines plate tectonics and the landforms it produces, then drainage basins and fluvial processes. Questions often link a boundary type to a landform and ask you to interpret a hydrograph or calculate a channel variable.
Core rules and concepts
- Plates move on the asthenosphere. Divergent boundaries create mid-ocean ridges and rift valleys. Convergent boundaries create ocean trenches and island arcs (ocean–ocean), mountain belts and volcanoes (ocean–continent), or fold mountains (continent–continent). Transform boundaries produce faults and earthquakes.
- Folding and faulting deform rock; seismic waves (P, S, surface) reveal Earth's interior.
- Weathering breaks rock in situ; erosion removes it. Physical, chemical and biological weathering differ.
- A drainage basin is an open system: inputs (precipitation), stores (soil, groundwater), transfers (infiltration, throughflow) and outputs (evapotranspiration, discharge).
- A storm hydrograph shows lag time, rising limb and recession. Urbanisation and impermeable rock shorten lag time and raise peak discharge.
Worked example
A channel is 5 m wide, mean depth 1.2 m and mean velocity 0.8 m/s. Cross-sectional area = 5 × 1.2 = 6 m². Discharge Q = area × velocity = 6 × 0.8 = 4.8 m³/s. Reasoning: discharge is a volume per second; the unit follows from m² × m/s.
Traps
Do not call weathering 'erosion'. Do not assume all convergent boundaries give the same landform. On hydrographs, lag time is the delay from rainfall peak to discharge peak, not the whole storm. Do not confuse stream order with discharge.