IGCSE Geography / Hazardous environments

Plates and plate boundaries revision notes

Edexcel International GCSE Geography (4GE1), chapter 3: Hazardous environments, specification point 3.1c, 3.S2. Free lesson.

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The Earth's plates move slowly because of convection currents in the mantle. Knowing how plates move at each boundary helps you explain the landforms and hazards found there.

How convection currents move plates

The Earth's thin, solid outer layer is the crust. It is broken into large pieces called plates, which rest on the hot, slowly flowing mantle. A convection current is a cycle of rising and sinking rock. It drags the plates along, so they move a few centimetres each year. The Earth's core heats the mantle. Hot rock becomes less dense, so it rises. Near the top, the rock spreads sideways under a plate and drags it along. The rock cools, becomes denser and sinks, ready to be heated again. The line where two plates meet is called a plate boundary.

How the four plate boundaries move

The type of boundary depends on the direction the plates move and, at some boundaries, which plate sinks. Oceanic crust is thin and dense. Continental crust is thicker and less dense. Destructive: plates move towards each other. The denser oceanic plate sinks beneath the continental plate. This is called subduction. Collision: two continental plates move together. Neither sinks, so the crust crumples upwards into fold mountains. Constructive: plates move apart. Magma, or molten rock, rises into the gap and forms new crust. Conservative: plates slide past each…

Examples and hazards at each boundary

Earthquakes can happen at all four boundary types. Volcanoes form only at destructive and constructive boundaries, where magma can reach the surface. Destructive: the Nazca plate sinks under the South American plate, building the Andes. Hazards include earthquakes and explosive volcanoes. Collision: the Indian plate pushes into the Eurasian plate, building the Himalaya. There are large earthquakes but no volcanoes. Constructive: the North American and Eurasian plates move apart at the Mid-Atlantic Ridge, where Iceland sits. Hazards include small earthquakes and gentle volcanoes.…

How to link plate and hazard maps

Use the arrows to identify movement, then match it to a boundary type and its hazards. The Pacific plate is the largest plate, and arrows show the direction of plate movement. At the Peru-Chile trench, the arrows point together. It is destructive, with earthquakes and volcanoes. At the Mid-Atlantic Ridge, the arrows point apart. It is constructive, with volcanoes too. At the San Andreas Fault, the arrows pass side by side. It is conservative, with earthquakes only. At the Himalaya, the arrows point together, but both plates are continental. It is a collision boundary, with earthquakes only.

Why conservative boundaries have no volcanoes

At a conservative boundary, the plates slide past each other. No gap opens and no plate sinks, so no crust is made or destroyed. As a result, no magma forms and there is nothing to erupt.