There are three types of volcanoes. The three types are Shield,Composite and Cindercone. Cindercone volcanoes are built from blobs of lava and eject big blobs of lava.Composite volcanoes have steep sides and are built up of cinders, volcanic ash and many other things.
Shield volcanoes are made up a dried up lava and are some of the biggest volcanoes are
Volcanoes erupt when moving plates collide and one plate slides on top of the other and releases lava.
Ring Of Fire
The ring of fire is a place that volcanoes surround. Most of the volcanoes are Shield volcanoes. The of fire has mostly active volcanoes.
Without volcanoes some islands wouldn't exist because they where made from dried up. Without lava Hawaii wouldn't be that big. That's why we need volcanoes