Plate tectonics

In short: The Earth’s crust consists of several large and small plates that slowly drift on the viscous mantle. Where they meet, mountains, volcanoes and earthquakes arise.

In more detail: The plates move a few centimetres a year, about as fast as fingernails grow. They are driven by heat currents inside the Earth.

In detail

• Moving apart: At mid-ocean ridges new crust forms, for example in Iceland.
• Collision: When two continental plates meet, they fold up mountains, like the Himalayas.
• Subduction: One plate dives under another. There lie deep-sea trenches and volcanic chains (Pacific Ring of Fire).
• Lateral sliding: As at the San Andreas Fault, where earthquakes arise suddenly.
• Continental drift: Alfred Wegener proposed the idea in 1912. About 250 million years ago all continents formed the supercontinent Pangaea (erdbeben-und-vulkane).