Are volcanoes good or bad? Good volcanoes or bad volcanoes?  The answer is yes to both!   Volcanoes can be good in that they “create” new land in places – like Hawaii. In fact, much of the earth’s crust today is the result of frequent volcano activity many thousands of years ago.  The bad part comes because of the destruction that often goes with an eruption.  Even in recent history, many people and animals have been killed – especially by certain types of volcanoes. What is going on in the inside that makes it a volcano at all?  First, most mountains are NOT volcanoes. The ones that are volcanoes have interesting structures inside that allows molten rock, from very deep in the earth, to rise up through the inside of the mountain.  Look the the cross section picture that follows. We can see that there are crevices and openings and holes and cracks inside that a hot magma can fill - this usually happens slowly.  (Remember magma is melted rock) Pressure will push the magma through the openings - if there is enough pressure there will be an eruption. There are a lot of different influences!  Like pressure and temperature and the types of rocks and how much water  - no two volcanoes are the same, but there are three main types.  Page 3 will show you! Let's look at how a volcano works. The magma pushes up through the conduits, out the vent and into the crater cone. image thanks to:   Thomas, R. & Sydenham, S. Volcanoes Here are some terms to be familiar with: eruption - when what is inside the volcano comes out magma - melted rock deep down in the earth lava - magma that surfaces and comes out of a volcano gases - air bubbles trapped in the magma ash and gas cloud - the plume that is first to appear at the beginning of the eruption vent - the opening on the surface of the volcano conduit - the pipe-like path the magma follows to the vent crater cone - a sunken bowl-shaped area Here is a picture of the outside of a volcano that is not erupting.  Thanks to the USGS for this picture of Mt. St. Helens before May 18, 1980. Just looks like a regular mountain, doesn't it?  But in this picture it is a sleeping volcano!  You can look at how it changed on page 2.