EVSC10001 · The Global Environment
Surface Processes & Landscapes
This chapter is the geomorphology block: how the five surface agents — rivers, groundwater & karst, glaciers, deserts and coasts — each erode, transport and deposit material and leave a diagnostic landform you can read backwards to name the process. It is the chapter most likely to appear as a Part A short-answer, where every question demands a labelled sketch, so the exam payoff is learning the diagram for each agent, not just the vocabulary.
What this chapter covers
- 01Rivers: discharge Q = w·d·v, stream power & the Hjulström curve
- 02Channel patterns — meandering vs braided & floodplain landforms
- 03Groundwater — aquifers, water table, porosity vs permeability
- 04Karst — dissolution chemistry, dolines, caves & towers
- 05Glaciers — mass balance, the equilibrium line, erosion & deposition
- 06Deserts — four causes of aridity, dunes & ephemeral wadis
- 07Coasts — refraction, longshore drift & sea-level control
- 08The shared erosion → transport → deposition logic
Meandering river & how it builds a floodplain (Part-A labelled diagram)
- +2Draw the labelled diagram first: a sinuous channel with, on each bend, a point bar (sediment) on the inside and a steep cut bank on the outside; add natural levees flanking the channel, a backswamp behind them, curved scroll bars tracing past positions, and a horseshoe oxbow lake off to one side. This labelled sketch carries the marks.
- +1Explain the secondary (helical) flow: water spirals across the bend so velocity is highest against the outside bank and lowest on the inside.
- +1Link flow to process: high-velocity water has the competence to erode the cut bank, while the slow inside loses energy and deposits the point bar — so the bend grows and the whole channel migrates sideways and downstream (arrow the migration on your diagram).
- +1Show oxbow formation: continued migration narrows the neck between two bends until a flood drives a neck cut-off; the river takes the short straight path, the abandoned loop is sealed by deposition, leaving the oxbow lake.
- +1Close with the floodplain link: repeated migration plus overbank flooding lays down levees, backswamp muds and scroll bars — the meander belt builds the floodplain.
Key terms
- Discharge (Q)
- The volume of water passing a channel cross-section per second, Q = w · d · v (width × mean depth × mean velocity), measured in m³/s ("cumecs").
- Hjulström curve
- A velocity-versus-grain-size plot with erosion, transport and deposition fields; sand is easiest to entrain while fine cohesive clay needs an anomalously high velocity to erode.
- Aquifer vs aquitard
- An aquifer is a rock unit that both stores and transmits groundwater; an aquitard (or aquiclude) is too impermeable to do so. Porosity = storage capacity; permeability = ability to let water flow.
- Karst
- A landscape developed on soluble rock (typically limestone) where dissolution opens caves and integrated underground drainage; it requires soluble rock + water + secondary porosity (joints/fractures).
- Equilibrium line
- The boundary on a glacier (the snow line) separating the upslope accumulation zone, where the glacier gains mass, from the downslope ablation zone, where it loses mass by melt and calving.
- Longshore drift
- The net along-shore transport of sediment driven by waves approaching the coast at an angle, building depositional landforms such as beaches, spits and barriers.
Surface Processes & Landscapes FAQ
How do you calculate river discharge?
Use the continuity equation Q = w · d · v: multiply channel width by mean depth to get the cross-sectional area, then multiply by mean velocity. The answer is in m³/s. For accurate gauging, split the channel into vertical panels, compute area × velocity for each, and sum them, because flow is slower near the bed and banks.
Why is fine clay harder to erode than sand?
Because clay particles are bound by cohesion and electrostatic attraction, so they need a higher velocity to lift than loose sand grains. This makes the Hjulström erosion threshold U-shaped: high at the clay end (cohesion), lowest around fine-medium sand, and high again at the gravel end (mass).
What makes a place a desert?
A dryland has a moisture deficit, where precipitation is less than potential evapotranspiration (P < PET). The four non-exclusive causes of aridity are descending subtropical-high (Hadley) air around 20-30° latitude, cold ocean currents on west coasts, continentality (distance from the ocean), and the rain-shadow of mountains.
What landforms tell you a glacier was once there?
Erosional signatures include U-shaped valleys, cirques, arêtes, horns, fjords and striations (scratches from abrasion). Depositional signatures include moraines (lateral, medial, terminal, ground), unsorted till, erratics, drumlins and sorted outwash.
How does karst topography form?
Rainwater takes up CO₂ (mostly from soil) to form carbonic acid, which dissolves limestone (CaCO₃ + H₂CO₃ → Ca(HCO₃)₂). Dissolution is fiercest in the wet tropics where soil-CO₂ is high, producing dolines (sinkholes), caves with speleothems and residual tower/cockpit karst.
Exam move
Treat every agent with one repeating template, because the exam rewards pattern recognition: name the agent and its energy source (gravity plus water, ice or wind), then split its path into erosion → transport → deposition and name the signature landform in each zone. Build a one-page \"landform atlas\" of five labelled sketches you can reproduce from memory — meander/oxbow (rivers), doline/cave/tower (karst), U-valley/moraine (glaciers), dune/wadi (deserts), stack/spit (coasts) — because Part A requires a labelled diagram every time. Anchor the rivers section with the two reusable tools, Q = w·d·v and the Hjulström order (gravel drops first, then sand, clay last), and the karst section with the dissolution equation plus the soil-CO₂ = wet-tropics link. Drill by drawing the diagram first and labelling it, then writing prose that walks the marker through your own labels.
