Geothermal energy is an important resource in volcanically active places such as Iceland and New Zealand.

How useful it is depends on how hot the water gets. This depends on how hot the rocks were to start with, and how much water we pump down to them.

Water is pumped down an "injection well", filters through the cracks in the rocks in the hot region, and comes back up the "recovery well" under pressure. It "flashes" into steam when it reaches the surface.

The steam may be used to drive a turbogenerator, or passed through a heat exchanger to heat water to warm houses. A town in Iceland is heated this way.

The steam must be purified before it is used to drive a turbine, or the turbine blades will get "furred up" like your kettle and be ruined.

Advantages

• Geothermal energy does not produce any pollution, and does not contribute to the greenhouse effect.
  
  
• The power stations do not take up much room, so there is not much impact on the environment.
  
  
• No fuel is needed.
  
  
• Once you've built a geothermal power station, the energy is almost free.
  It may need a little energy to run a pump, but this can be taken from the energy being generated.

Disadvantages

• The big problem is that there are not many places where you can build a geothermal power station.
  You need hot rocks of a suitable type, at a depth where we can drill down to them.
  
  
• The type of rock above is also important, it must be of a type that we can easily drill through.
  
  
• Sometimes a geothermal site may "run out of steam", perhaps for decades.
  
  
• Hazardous gases and minerals may come up from underground, and can be difficult to safely dispose of.