The front of the block is cut open to show the lithosphere, the sinking plate and the mantle convection currents underneath. Stress builds as the plates move and is released in earthquakes, with the focus marked on the cut face and seismic waves spreading over the surface.
- What are the three types of plate boundary?
- Convergent (destructive) boundaries, where plates move together and one may sink; divergent (constructive) boundaries, where plates move apart and new crust forms; and transform (conservative) boundaries, where plates slide past each other.
- What causes tectonic plates to move?
- Heat from the Earth's core drives slow convection currents in the mantle, which drag the plates along. Sinking plates also pull the rest of the plate behind them (slab pull), and plates slide away from high mid-ocean ridges (ridge push).
- What happens when an oceanic plate meets a continental plate?
- The denser oceanic plate sinks under the continent (subduction), forming a deep ocean trench. It melts as it goes down, and the magma rises to form volcanoes and mountains, like the Andes. Large earthquakes happen along the sinking plate.
- How were the Himalayas formed?
- The Indian Plate has been colliding with the Eurasian Plate for about 50 million years. Continental crust is too light to sink, so it crumpled and thickened into fold mountains. Everest (8,849 m) is still rising a few millimetres a year.
- What is sea-floor spreading?
- At mid-ocean ridges the plates move apart and magma rises to fill the gap, making new ocean floor. The new rock records the direction of Earth's magnetic field, which reverses every so often, leaving matching magnetic stripes on both sides of the ridge.
- How fast do tectonic plates move?
- Between about 1 and 10 cm a year: roughly as fast as your fingernails grow. The Nazca Plate moves about 7 cm a year; the Atlantic widens about 2.5 cm a year.