Physical Geography: Geomorphology
This section covers Geomorphology, the AHSEC unit on Earth's internal structure, plate tectonics, denudation and landform evolution. Questions usually ask you to distinguish processes, interpret landform evidence and apply simple gradient calculations.
Core rules
- The Earth's interior is divided into crust, mantle and core; the Moho separates crust from mantle, and the Gutenberg discontinuity separates mantle from core.
- Plate boundaries are divergent (mid-ocean ridges), convergent (trenches, fold mountains, volcanoes) and transform (faults). The Himalayas result from Indian–Eurasian convergence.
- Weathering is in-situ breakdown; erosion involves transport by water, wind, ice or waves. Do not use the terms interchangeably.
- Fluvial stages: youthful V-shaped valleys and rapids; mature wide valleys and meanders; old age floodplains and peneplains. Karst landscapes form on limestone by carbonation; glacial landscapes form cirques, arêtes and U-shaped valleys.
Worked example
A river falls from 900 m at its source to 300 m at a point 24 km downstream. Fall = 600 m. Average gradient = 600 ÷ 24 = 25 m/km. As a ratio, 25 m per 1,000 m = 1:40. A gradient of 25 m/km is steep, so the reach is likely youthful, with rapids and a V-shaped valley. Lower downstream, a gradient of 2 m/km would suggest meanders and deposition.
Traps
- Calling exfoliation chemical: it is mechanical.
- Treating a U-shaped valley as fluvial; it is glacial.
- Confusing the Deccan Traps (volcanic) with fold mountains.
- Ignoring base level when explaining deposition.