Earth's Surface Processes and Landforms
This domain covers weathering, erosion, deposition, mass wasting, streams, groundwater, glaciers, wind, coasts, and soils. Exam items often ask you to predict landform change from process, gradient, discharge, or sediment size.
Core rules and concepts
- Weathering breaks rock in place; erosion transports sediment; deposition lays it down.
- Chemical weathering is favored by warm, wet conditions; physical weathering increases surface area and speeds chemical breakdown.
- Streams erode on cut banks and deposit on point bars; velocity increases with gradient and discharge but decreases with roughness.
- Sediment settles by size and density: gravel drops first, clay last; well-sorted sediment suggests consistent transport.
- Glaciers carve U-shaped valleys and deposit unsorted till; rivers carve V-shaped valleys and deposit sorted sediment.
- Groundwater dissolves limestone to form karst caves, sinkholes, and disappearing streams.
Worked example
A stream drops from 1,200 m at its headwaters to 400 m at its mouth over 80 km. Gradient = 800 m ÷ 80,000 m = 0.01, or 10 m/km (1%). The steep upper reach transports coarse gravel and boulders; the lower reach has a lower gradient, so velocity falls and fine sand, silt, and clay are deposited on floodplains and deltas. This explains the downstream fining of sediment.
Traps that cost marks
- Calling weathering “erosion” when material has not moved.
- Assuming fast water always deposits; deposition occurs when velocity drops.
- Confusing glacial till (unsorted) with outwash (sorted by meltwater).
- Reversing cut-bank erosion and point-bar deposition on meanders.