What's covered
Key facts
Earthquakes are caused by sudden movement at or near tectonic plate boundaries, which releases stored energy as seismic waves.
Drought is defined by a sustained shortfall in precipitation relative to the local average — it is about water deficit, not high temperature alone.
The epicentre is the point on Earth's surface directly above the focus (hypocentre) of an earthquake.
A drought is a prolonged period of below-average rainfall that leads to water shortages.
The focus (hypocentre) of an earthquake is the point inside Earth where the rupture begins and energy is first released.
A flood is the overflow of water that submerges land which is normally dry, typically after heavy rainfall, snowmelt or a storm surge.
Lava is the molten rock that erupts from a volcano onto the surface (it is called magma while still inside the Earth).
A natural hazard is a natural process or event with the potential to cause harm; it becomes a natural disaster only when it significantly harms people, property or economies.
Most, but not all, earthquakes and volcanoes occur at plate boundaries; some occur within plates (intraplate earthquakes and hotspot volcanoes such as Hawaii). [USGS, Understanding plate motions [This Dynamic Earth]]
A tropical storm in the North Atlantic (and the North-East Pacific) is called a hurricane.
Sample questions
A taste of the 23 questions in this topic — answers marked. Sign up to practise the full set with spaced repetition.
What causes earthquakes?
- •heavy rainfall saturating soil and causing it to collapse
- •magma forcing its way through cracks in the Earth's crust
- •strong winds creating pressure waves in the ground
- ✓sudden movement at or near tectonic plate boundaries
What is a flood?
- •a large wave caused by an underwater earthquake or volcanic eruption
- •a long period of below-average rainfall causing water shortages
- •a tropical storm with very strong winds and heavy rainfall
- ✓water covering normally dry land, often after heavy rainfall or storm surge
What is a volcano?
- •a crack in the Earth's surface caused by tectonic plate movement
- •a deep trench in the ocean floor where plates move apart
- •a mountain formed entirely from layers of deposited sediment
- ✓an opening in Earth's crust releasing magma, ash, and gases
What is a drought?
- ✓a prolonged period of below-average rainfall leading to water shortages
- •a sudden drop in temperature causing frost and ice to damage crops
- •an extreme storm bringing heavy rainfall and strong winds in a short period
- •water covering land that is normally dry after heavy rain
Why do earthquakes and volcanoes often occur in the same locations?
- •Both are caused by the same underground rivers of molten rock
- ✓Both result from tectonic plate movement at plate boundaries
- •Earthquakes weaken the crust, allowing magma to reach the surface
- •Volcanic eruptions trigger earthquakes in nearby areas
What is the difference between a natural hazard and a natural disaster?
- •A disaster is rated higher than a hazard on scientific scales
- ✓A hazard becomes a disaster when it significantly harms people
- •A hazard is always a weather event; a disaster is geological
- •Natural disasters are always caused by humans; hazards are purely natural
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