Most earthquakes and volcanoes happen near plate boundaries. In an earthquake, plates stick, stress builds up, and then the rock suddenly slips, sending out seismic waves. The point underground where it starts is the focus, and the point on the surface above it is the epicentre. A seismometer records the waves, and the magnitude scale measures the energy released.
Volcanoes form where magma reaches the surface, often at subduction zones and divergent boundaries, and at hot spots like Hawaii. People cannot stop these hazards, but they can reduce harm: earthquake-proof buildings with flexible frames, drills so people know what to do, monitoring volcanoes for small earthquakes and swelling ground, and warning systems for tsunamis.
Worked example
Why is Japan at high risk of earthquakes?
- Japan sits where several plates meet.
- Stress builds up and is released suddenly along these boundaries.
Answer:So earthquakes are common there.
Key words
- epicentre
- the point on the surface above an earthquake's start
- seismometer
- an instrument that records earthquake waves
- magnitude
- a measure of the energy an earthquake releases
- tsunami
- a giant wave caused by an undersea earthquake
New questions every time.
NGSS-referenced: MS-ESS3-2