Supervolcanoes are on a much bigger scale than normal volcanoes. They are capable of producing huge volcanic eruptions - up to 1000 cubic km of ash/lava - and this would have global consequences. They occur when magma rises up to the crust from a hot spot but is unable to break through. Pressure builds up until the crust is unable to contain the pressure and explodes. An example of a supervolcano which formed at a hotspot is Yellowstone, USA. If it erupted it would probably destroy 10,000km of land, kill 87,000 people, affect transport, electricity, water and farming. The UK would await the arrival of ash around 5 days later. Global climates would change and crops would fail. However, now, it is a major tourist attraction and there are lots of activities availible for a range of people such as hiking, cycling, boating, camping and wild-life viewing.