We are learining about Volcanoes. I know that the Roman god of fire is called Vulcan.
An eruption is caused by molten rock heating up. This makes it grow bigger in size. Now it has expanded, it needs more room and moves into any empty spaces. When these spaces are blocked the molten rock has nowhere to go.
Dormant means that it could wake up at any time. Extinct means that its all gone and will not come back again. Some volcanoes will not erupt again.