Open the app
  1. Home
  2. Lessons
  3. KS3 Geography
  4. Plate boundaries, earthquakes and volcanoes

Plate boundaries, earthquakes and volcanoes

🎬 The doodle video for this lesson is coming soon. Subscribe on YouTube to see it first.

Most earthquakes and volcanoes happen where plates meet. What happens depends on how the plates move.

Types of plate boundary

Constructive (divergent): plates move apart. Magma rises to form new crust, with gentle volcanoes. Example: the Mid-Atlantic Ridge, which runs through Iceland.
Destructive (convergent): oceanic crust sinks under continental crust. This causes explosive volcanoes and strong earthquakes. Example: the west coast of South America (the Andes) and Japan.
Collision: two continental plates push together and fold up into mountains, such as the Himalayas.
Conservative: plates slide past each other. No volcanoes, but earthquakes. Example: the San Andreas Fault in California.

Earthquakes

Pressure builds up where plates stick, then is released suddenly as an earthquake.
The point underground where it starts is the focus; the point on the surface above it is the epicentre.
Scientists measure earthquake strength on the moment magnitude scale. Undersea earthquakes can cause tsunamis, as in Japan in 2011.

Volcanoes

Volcanoes form where magma reaches the surface. Once it erupts it is called lava.
The Pacific Ring of Fire is a ring of volcanoes and earthquake zones around the Pacific Ocean.
In 2010 ash from the Icelandic volcano Eyjafjallajokull stopped many flights across Europe for days.
Worked example

Why are earthquakes and volcanoes common in Japan?

  1. Japan lies on destructive plate boundaries.
  2. Oceanic plates sink beneath the plates Japan sits on, which melts rock and forms magma: volcanoes.
  3. The plates stick and slip as they move, releasing energy: earthquakes.

Answer: It sits on destructive boundaries where plates sink, causing both volcanoes and earthquakes.

Key idea

Constructive: apart (Iceland). Destructive: oceanic plate sinks (Andes, Japan): explosive volcanoes and big earthquakes. Collision: fold mountains (Himalayas). Conservative: slide past (San Andreas), earthquakes only. Focus underground; epicentre above it. Ring of Fire around the Pacific.

The interactive lesson includes the diagrams for this topic.

Check you have got it

Answer 6 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.

Practise this lesson free (6 questions)All KS3 Geography lessons