How does a volcano happens?

Question

Help!

Answer 1

There are basically two types.  One is where the crust is melted as it moves over a hot spot.  That is what Yellowstone and Hawaii are.  Most are cause from crust of one plate getting pushed under another.  The water in the crust causes the melting point of the rock around it to decrease.  The molten rock rises through cracks or pushes its way up and eventually finds an opening.  Those kinds of volcanoes are often explosive like Mount St. Hellens

Answer 2

over millions of years of lava flowing (layer by layer)out from the surface of the earth.the nature of the magma detemines whether it forms a beautiful cone like mt fuji or a mass of ragged mount....

Answer 3

well u mean when it erupts

it happens by the gas and pressure under the earth builing up over the years and when it cant take no more pressure it sends the lava from under ground up bursting

Answer 4

A volcano does not happen.

Volcanic eruptions happen.

An eruption begins when pressure on a magma chamber forces magma up through the conduit and out the volcano's vents.  When the magma chamber has been completely filled, the type of eruption partly depends on the amount of gases and silica in the magma.  The amount of silica determines how sticky (level of viscosity) the magma is and water provides the explosive potential of steam.