Plates & their boundaries

Earth's crust is broken into tectonic plates that move slowly on the mantle below. Most volcanoes and earthquakes happen at plate boundaries:

• Constructive (divergent) — plates move apart; magma rises to form new crust and gentle volcanoes (e.g. mid-ocean ridges).
• Destructive (convergent) — plates move together; the denser oceanic plate is forced down in subduction, melting to feed explosive volcanoes and causing strong earthquakes.
• Conservative — plates slide past each other; crust is neither made nor destroyed, but friction triggers earthquakes.

Which boundary subducts?

Volcano types & earthquake terms

Two contrasting volcano types:

• Shield volcano — wide and gently sloping, built from runny (low-viscosity) lava at constructive boundaries.
• Composite (strato) volcano — tall and steep, built from alternating layers of sticky lava and ash at destructive boundaries.

Key parts: magma chamber (store of molten rock), vent (pipe to the surface) and crater (opening at the top).

For earthquakes: the focus is the point underground where it starts; the epicentre is the point on the surface directly above it; magnitude (measured on the Richter/moment scale) is the energy released.

Match each term to its meaning

Tap a term on the left, then its matching meaning on the right.

River processes

In its drainage basin a river moves water by interception, infiltration, throughflow, groundwater flow and overland flow. The river itself does three kinds of work:

• Erosion — wearing away the bed and banks (hydraulic action, abrasion, attrition, solution).
• Transport — carrying the load by traction, saltation, suspension and solution.
• Deposition — dropping the load when the river loses energy.

From waterfall to delta

River processes create landforms along the long profile:

• Waterfall — where a river crosses hard rock onto softer rock, which is undercut to form a plunge pool and gorge.
• Meander — a bend where the fast outer bank is eroded (river cliff) and the slow inner bank builds up (slip-off slope).
• Oxbow lake — a cut-off loop left when a meander neck is breached.
• Flood plain & levées — flat valley floor built from deposited alluvium; raised banks (levées) form beside the channel.
• Delta — sediment dropped where the river meets a sea or lake.

Erosion, transport or deposition?

Tap a process or landform, then tap the group it belongs to.

Your turn — river discharge

Coastal landforms

The sea erodes, transports and deposits to make coastal landforms:

• Erosional: cliffs and wave-cut platforms; on a headland a crack widens into a cave → arch → stack → stump.
• Depositional: beaches in sheltered bays, and spits where longshore drift carries material across a gap.

In warm, clear, shallow tropical seas, coral reefs grow; along muddy tropical coastlines, salt-tolerant mangrove swamps develop and protect the shore.

Put it in order

Measuring the weather

Weather data is collected with standard instruments, many kept in a Stevenson Screen — a white, louvred, ventilated box on legs about 1.25 m off the ground that shades thermometers from direct sun while letting air flow freely.

• Rain gauge — precipitation; maximum–minimum thermometer — temperature range.
• Wet-and-dry bulb thermometer (hygrometer) — humidity; barometer — air pressure.
• Anemometer — wind speed; wind vane — wind direction; sunshine recorder — hours of sunshine.

Why is it white and louvred?

Equatorial vs hot desert climate

Cambridge studies two contrasting climates:

• Equatorial — hot all year (around 26–28 °C), very small annual temperature range, heavy convection rainfall most days; supports dense tropical rainforest.
• Hot desert — very hot days but cold nights (large daily range), high annual range, very little rain; supports sparse, drought-adapted desert vegetation such as cacti.

Factors affecting climate include latitude, pressure systems and winds, distance from the sea, altitude and ocean currents.

Your turn — annual temperature range

Rainforest, desert & deforestation

In an ecosystem, climate, soil, vegetation and wildlife are closely linked:

• Tropical rainforest — layered (emergent, canopy, understorey, forest floor), hugely biodiverse; nutrients are held mostly in the plants, so soils are thin.
• Hot desert — sparse, specially adapted plants and animals cope with heat and drought.

Deforestation of the rainforest is caused by logging, farming, cattle ranching, mining and roads. Effects include soil erosion, loss of biodiversity and more carbon dioxide adding to global warming.

Case study flag: Cambridge expects a named example of an ecosystem under threat (e.g. a named area of rainforest). Check any specific figures against your class notes before quoting them.

Your turn — total rainfall

Which volcano is broad and gentle?

The big ideas to know

You've covered the core of Cambridge Theme 2 — The Natural Environment. Press Finish to see your score.