Plate Tectonics and Hazards

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Plate Tectonics

Cross-section showing Earth's layers and tectonic plates

Plate tectonics is the scientific theory that explains how large pieces of Earth’s outer layer move. These pieces are called tectonic plates.

Earth has several layers. The thin, solid outer layer is the crust. The crust and the uppermost part of the mantle form the lithosphere, which is broken into tectonic plates. Beneath it is the hotter, softer asthenosphere.

Heat from inside Earth causes slow movement in the mantle. This movement helps drive the plates. Tectonic plates move only a few centimetres each year, about as fast as fingernails grow.

Plates may move towards each other, away from each other or past each other. The places where plates meet are called plate boundaries.

Earthquakes and Volcanoes

Diagram showing an earthquake fault and a volcano at a plate boundary

At some plate boundaries, rocks are squeezed, pulled or forced past one another. Stress builds up until the rocks suddenly move. This releases energy as vibrations called seismic waves. The shaking caused by this sudden movement is an earthquake.

The underground point where an earthquake begins is the focus. The point on Earth’s surface directly above the focus is the epicentre. Earthquakes can damage buildings, roads and bridges, and undersea earthquakes can sometimes cause tsunamis.

Volcanoes often form where one plate moves beneath another, where plates move apart, or above hotspots. Melted rock called magma can rise through cracks in Earth’s crust. When magma reaches the surface, it is called lava.

A volcanic eruption may release lava, ash, gases and rock fragments. Volcanoes can create new land and produce fertile soils, but eruptions can also threaten people, animals and communities.

Plate Boundaries and Hazards

At a constructive boundary, plates move apart. Magma rises and cools to form new crust. These boundaries commonly produce volcanic activity and shallow earthquakes.

At a destructive boundary, one plate may sink beneath another in a process called subduction. This can cause powerful earthquakes, deep ocean trenches and volcanoes.

At a conservative boundary, plates slide past each other. Crust is not created or destroyed, but friction can cause sudden and damaging earthquakes.

Scientists monitor earthquakes and volcanoes using instruments such as seismometers, satellites and gas sensors. Monitoring helps communities prepare, practise emergency plans and reduce the effects of natural hazards.