those which occur at plate margins. There are so many volcanoes around the boundary of the Pacific plate that it is known as the'Pacific ring of fire'.
Volcanoes, such as those of the Hawaiian islands, force out large amounts of thin lava so that the volcanic cone is low and spreads out to cover a wide area. Layer after layer of lava, ash and debris builds up gradually to
form the elegantly shaped cone.
In some volcanoes, the vent
tween eruptions by a plug of rock. Slowly, the pressure under the plug builds up and the volcano erupts with such force and speed that no one has any time to escape.
For example, the ancient city of Pompeii in south-west italy was buried by an erupion of Vesuvius in AD 79.