For each 100 metres you go below ground the temperature increases by 3 C. If water comes into contact with this hot rock it can produce very hot water and even steam. In such countries as Iceland this steam can be used to produce electricity. The advantages are the cheapness and simplicity of obtaining the steam. The obvious disadvantage is that not all areas have geothermal energy readily available. Click on the volcano to go to an interesting site about geothermal energy in Southampton.
Nuclear power has lots of advantages but two major disadvantages.
It is one of the cheapest forms of energy production and the electricity generated produces no sulphur or carbon dioxide. It has minimal environmental impact and the fuel used can be from recycled sources or produced from raw materials. The two big disadvantages are the huge cost of waste disposal and the health problems that could result from accidental discharges of activity. The future of nuclear power will almost certainly lie in the area of small self-contained reactors such as the new pebble bed reactor. The pebble bed reactor can be used in small areas, especially in the third world, it is fail-safe and relatively cheap.