A supervolcanoes is a volcano capable of producing a volcanic eruption with an ejecta volume greater than 1000 km3
They are formed when magma rises from a hotspot but is unable to break through the crust, causing the pressure to build up in a growing magma pool until the crust is unable to contain it
Supervolcanoes typically do not have cones; instead, they have calderas, which form after large eruptions when the emptied magma chamber is unable to support the volcanic edifice above it, causing it to collapse
Effects of an eruption: Yellowstone
Destroy 10,000 km2
Kill 87,000 people
Buildings within 1000 km would be covered with 15 cm of ash
1 in 3 people affected would die
Ash would reach the UK within 5 days
Global climates would change, crop would fail and many people would die